With water from recent rains accumulating wherever there are abandoned tires, empty containers, and puddles, there is a danger of increased mosquito populations.
It happens around here whenever it rains, which, granted, is not often. Because we do live in a dry desert, we often forget that mosquitoes are a part of the desert. Nevertheless, standing water from any source is bound to attract a mosquito looking for a place to lay eggs. Before we know it, we are slapping at the pesky critters. Besides an annoyance, mosquitoes are a concern because they do carry a risk of disease, including West Nile Virus and encephalitis.
State and county health departments in Arizona are always concerned after rains fall because they know that the risk of disease is real. It is up to you and I to take proactive steps to eliminate these potential breeding sites and protect not only our neighbors, but ourselves as well. With the break in the monsoon storms, now is a good time to search out and eliminate any standing water that could turn into breeding grounds for mosquitoes. Here are some suggestions of what you might need to do.
■ Walk around your property. Search out, drain, and get rid of anything that can hold water, such as tin cans, containers, and used tires. Old tires rank among the most important mosquito-breeding sites in the country.
■ Drill holes in the bottoms of your recycling containers and outdoor planters. Check uncovered junk piles for standing water and drain them immediately.
■ Clean any clogged roof gutters. Check storm drains, leaky outdoor faucets, and window wells for persistent water pools.
■ Empty accumulated water from wheelbarrows, boats, cargo trailers, pet dishes, toys, and ceramic pots. If possible, turn these items over when not in use.
■ Change the water in the birdbath every few days. Do not allow water to stagnate in ornamental pools, water gardens, animal watering dishes and swimming pools or their covers. Swimming pools should be cleaned and chlorinated when not in use.
■ If you know of a swimming pool or other decorative pond that is not being properly cared for, speak kindly to the owner and see if he or she will soon be doing the maintenance. If you know of abandoned pools with no one to care for them, contact the Pinal County Division of Environmental Health on Vector Control & Surveillance at (520) 866-6864 for more information.
■ Survey and decide whether or not you need to alter the landscape of your property to eliminate standing water. Keep in mind that during our warm spring weather, mosquitoes can breed in any puddle of water.
■ Larvicides, insecticides that kill young mosquitoes, are highly effective in controlling immature mosquitoes and should be considered when standing water cannot be eliminated.
■ Make sure all of your window and door screens are “bug tight.”
■ Check your outdoor lights. Incandescent lights attract mosquitoes, whereas fluorescent lights neither attract nor repel mosquitos. Consider changing to fluorescent bulbs where possible.
■ Stay indoors at dawn, dusk, and in the early evening when mosquitoes are most active. If you must go outdoors, wear a long-sleeved shirt and pants.
■ Insect repellents when applied (sparingly) to exposed skin deter mosquitoes from biting. Spray thin clothing with repellent because mosquitoes can bite through loosely woven cloth. The American Academy of Pediatrics recommends that repellents used on children contain no more than 10 percent DEET, the active ingredient in mosquito repellents. Be sure to follow all directions on product labels. Call our Cooperative Extension office for a bulletin that will describe the proper use of repellents.
■ If you have horses, goats, sheep and other livestock animals, check with your veterinarian for vaccination requirements. Horses, which are particularly susceptible, must be vaccinated for protection against the disease.
■ Aerate ornamental pools to prevent development of mosquito larvae, or stock them with mosquito fish. Fish are an excellent treatment for ponds and horse troughs. Mosquito fish have a voracious appetite for mosquitoes and their larvae. As I watch the fish in our back yard fishpond, the mosquito fish seem to be saying to mosquitoes and other passing insects, “Please fly close to the surface of the water!” and “Please come lay your eggs in my pond!” They have huge appetites for insects.
■ Learn all that you can about mosquitoes and West Nile Virus. A good source of information is the Pinal County Vector Control & Surveillance website called the Pinal County West Nile Virus Web Page. It can be found at http://www.pinalcounty.org/EnvHealth/WNV/ on the internet. Look at the bottom of the lower left hand column named “Hot Topics” and click on West Nile Virus. I would encourage anyone with questions about the disease, or the county’s effort to help us control these vectors, to visit this site.
In order to protect ourselves from disease, it is important that all of us work together to minimize the risks that come from living in the desert.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Wednesday, July 24, 2013
Tuesday, July 16, 2013
Preventing Salt Damage In Plants
One of the challenges to growing a successful garden in the desert is the proper management of salt.
Since salt accumulation is unique to desert environments, those new to desert gardening may not recognize the effects that salt accumulations can have on plants. When you see wilting plants, leaves with tips and edges turning brown, and salt-induced iron deficiencies know that you probably are experiencing the buildup of salt in and around your garden and landscape plants. Fortunately, salts usually can be successfully managed with a little planning and attention to watering habits.
Salts are chemical compounds of common, everyday elements that are broken down from rock formations. Soluble in water, they are easily dissolved as rain or irrigation water moves through the soil profile. In high rainfall areas, the large volume of water moving through the soil carries these compounds down through and past the root systems of plants so that accumulations never reach toxic levels. This is why salts are rarely a problem in the less arid areas of the country.
In the desert, however, rainfall is rarely sufficient to dissolve and leach salts below the root systems of plants. Many native plants are adapted to these conditions and do not seem to be bothered by salt in their environment. Those native plants that are susceptible to salts simply do not grow where salt accumulations in the soil have reached toxic levels. When susceptible, non-native plants are brought into the desert and planted into a salty environment, trouble occurs.
Salt injury can occur at any time during the year but seems to be more frequent during the hot summer months, when plants are under peak stress and using water at a rapid pace. The increased metabolism of plants during the summer speeds the accumulation of salts and hastens the appearance of symptoms in plant tissues.
Salts, dissolved in water, are generally absorbed by plants through the roots. Once inside, they move up through the water-conducting tubes to the leaves. When the water within the leaves evaporates and exits through the process of transpiration, the salts are left behind. When sufficient salt has been deposited to reach levels toxic to that particular plant, symptoms appear.
The most common symptom of salt injury in plants is the dying back of tips and edges of leaves. As salts accumulate, the plant tissue in these areas may turn yellow first, but this is not always the case. The browning of these tissues is caused by the actual death of cells and tissues. As the condition worsens, the dead, brown areas may get larger until the entire leaf dies and falls from the plant.
Sometimes salt accumulates in the soil around roots to the point that it prevents the absorption of water by the plant. It is easy to tell when this happens by looking at the leaves and soft stems. The soil will be moist around the plant, but the plant itself will show water stress symptoms, including hot, wilting, drooping leaves and stems. Often times, these symptoms will be accompanied by the tip and margin burn symptoms described earlier.
Another symptom of salt problems is iron deficiency. Because salts have a basic or alkaline pH, they can raise the soil pH to the point where iron and other nutrients are insoluble in the soil. High soil pH values make it difficult, if not impossible, for the plant to absorb and use these essential nutrients.
Leaves of tender plants show iron deficiency symptoms when they start to turn a pale to brilliant yellow color, but the veins of the leaves stay green. This is a sign of iron deficiency. When this happens, cut back on the watering frequency while increasing the length of time the water is being applied to the soil and treat the plant with a chelated iron fertilizer product. The leaves should turn green within a week to 10 days.
The solution to salt problems is usually fairly simple. In most cases, salt accumulations are caused by frequent, shallow irrigations. First, know and understand that the roots of most plants go deep into the soil and that when we are irrigating, no matter whether it is with a hose or a drip system, that the entire root system must be moistened to move the salts down and out of the root zone. Remember also that a salt layer can form out laterally from the tree. Most people have seen a white ring around their irrigated plants. That is the salt layer. Make sure that you are irrigating out to the edge of the plant and not just next to its stem or trunk.
There is a handy rule of thumb to help estimate the depth needed to properly irrigate plants. We call it the “rule of 12's.” The rule of 12's states simply that bedding plants, turf, vegetables, flowers and other shallow rooted plants need to be irrigated to a depth of 12 inches. The soil around shrubs needs to be irrigated to 24 inches and trees should be moistened to a depth of 36 inches.
I like to use a soil probe to see how far the water has sunk into the ground. The probe slides easily into wet soil but stops abruptly when it reaches the dry layer. I place my fingers on the barrel of the probe at the point where the probe emerges from the soil. Then, when I pull out the probe, I can easily see the depth of water penetration.
Second, during irrigations, turn down the volume of water coming from the hose to a trickle and slowly fill the basin around the plant. The extra water from the longer irrigations will sink deeper into the soil and move the salts down and away from the plant. There is an added benefit to doing this. Water stored deep in the ground will allow lower roots to help support the plant’s water needs and lengthen out the time necessary between irrigations. For those using drip irrigation systems, increase the duration of the irrigation set to provide the volume of water needed to leach the salts.
For leaves that already have dead tips or margins, there isn’t much that can be done to alleviate the damage, because the tissue is already dead; but new leaves that grow after treatment should not show new damage if the problem has been solved.
Sometimes the soil does not readily accept water because of a hard layer, like caliche, or because of a chemical imbalance, like an overabundance of sodium. Physical barriers can be fixed by digging or drilling holes down through the compacted layer to a more permeable soil layer which will accept the salty water and move it away from the root zone. Backfill the holes with sand to help keep the hole from caving in and reconsolidating.
If sodium salt is a problem, water may stand for hours and sometime even days before it sinks in or evaporates away. The rule of thumb for managing sodium is this: If it takes more than one hour for water around a plant to sink in, treat for sodium.
Gypsum, available by the bag at most nurseries, is an ideal way to deal with sodium problems. Sprinkled on the surface of the ground and raked gently in before a deep irrigation, gypsum will replace the sodium in the soil with calcium. The deep irrigation then leaches the sodium out of the root zone.
Soil sulfur can also be used to eliminate sodium but it will only work if there is calcium or free lime already in the soil. Sulfur, moistened with water, becomes sulfuric acid which combines with the calcium to form gypsum. The process then proceeds as described above.
The coming warm weather months are a difficult time for plants, even those that are adapted to the extreme heat of the desert. Salt damage is one of the more common problems that gardeners must face during this time. By correctly managing irrigation water, most salt problems can be prevented.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Since salt accumulation is unique to desert environments, those new to desert gardening may not recognize the effects that salt accumulations can have on plants. When you see wilting plants, leaves with tips and edges turning brown, and salt-induced iron deficiencies know that you probably are experiencing the buildup of salt in and around your garden and landscape plants. Fortunately, salts usually can be successfully managed with a little planning and attention to watering habits.
Salts are chemical compounds of common, everyday elements that are broken down from rock formations. Soluble in water, they are easily dissolved as rain or irrigation water moves through the soil profile. In high rainfall areas, the large volume of water moving through the soil carries these compounds down through and past the root systems of plants so that accumulations never reach toxic levels. This is why salts are rarely a problem in the less arid areas of the country.
In the desert, however, rainfall is rarely sufficient to dissolve and leach salts below the root systems of plants. Many native plants are adapted to these conditions and do not seem to be bothered by salt in their environment. Those native plants that are susceptible to salts simply do not grow where salt accumulations in the soil have reached toxic levels. When susceptible, non-native plants are brought into the desert and planted into a salty environment, trouble occurs.
Salt injury can occur at any time during the year but seems to be more frequent during the hot summer months, when plants are under peak stress and using water at a rapid pace. The increased metabolism of plants during the summer speeds the accumulation of salts and hastens the appearance of symptoms in plant tissues.
Salts, dissolved in water, are generally absorbed by plants through the roots. Once inside, they move up through the water-conducting tubes to the leaves. When the water within the leaves evaporates and exits through the process of transpiration, the salts are left behind. When sufficient salt has been deposited to reach levels toxic to that particular plant, symptoms appear.
The most common symptom of salt injury in plants is the dying back of tips and edges of leaves. As salts accumulate, the plant tissue in these areas may turn yellow first, but this is not always the case. The browning of these tissues is caused by the actual death of cells and tissues. As the condition worsens, the dead, brown areas may get larger until the entire leaf dies and falls from the plant.
Sometimes salt accumulates in the soil around roots to the point that it prevents the absorption of water by the plant. It is easy to tell when this happens by looking at the leaves and soft stems. The soil will be moist around the plant, but the plant itself will show water stress symptoms, including hot, wilting, drooping leaves and stems. Often times, these symptoms will be accompanied by the tip and margin burn symptoms described earlier.
Another symptom of salt problems is iron deficiency. Because salts have a basic or alkaline pH, they can raise the soil pH to the point where iron and other nutrients are insoluble in the soil. High soil pH values make it difficult, if not impossible, for the plant to absorb and use these essential nutrients.
Leaves of tender plants show iron deficiency symptoms when they start to turn a pale to brilliant yellow color, but the veins of the leaves stay green. This is a sign of iron deficiency. When this happens, cut back on the watering frequency while increasing the length of time the water is being applied to the soil and treat the plant with a chelated iron fertilizer product. The leaves should turn green within a week to 10 days.
The solution to salt problems is usually fairly simple. In most cases, salt accumulations are caused by frequent, shallow irrigations. First, know and understand that the roots of most plants go deep into the soil and that when we are irrigating, no matter whether it is with a hose or a drip system, that the entire root system must be moistened to move the salts down and out of the root zone. Remember also that a salt layer can form out laterally from the tree. Most people have seen a white ring around their irrigated plants. That is the salt layer. Make sure that you are irrigating out to the edge of the plant and not just next to its stem or trunk.
There is a handy rule of thumb to help estimate the depth needed to properly irrigate plants. We call it the “rule of 12's.” The rule of 12's states simply that bedding plants, turf, vegetables, flowers and other shallow rooted plants need to be irrigated to a depth of 12 inches. The soil around shrubs needs to be irrigated to 24 inches and trees should be moistened to a depth of 36 inches.
I like to use a soil probe to see how far the water has sunk into the ground. The probe slides easily into wet soil but stops abruptly when it reaches the dry layer. I place my fingers on the barrel of the probe at the point where the probe emerges from the soil. Then, when I pull out the probe, I can easily see the depth of water penetration.
Second, during irrigations, turn down the volume of water coming from the hose to a trickle and slowly fill the basin around the plant. The extra water from the longer irrigations will sink deeper into the soil and move the salts down and away from the plant. There is an added benefit to doing this. Water stored deep in the ground will allow lower roots to help support the plant’s water needs and lengthen out the time necessary between irrigations. For those using drip irrigation systems, increase the duration of the irrigation set to provide the volume of water needed to leach the salts.
For leaves that already have dead tips or margins, there isn’t much that can be done to alleviate the damage, because the tissue is already dead; but new leaves that grow after treatment should not show new damage if the problem has been solved.
Sometimes the soil does not readily accept water because of a hard layer, like caliche, or because of a chemical imbalance, like an overabundance of sodium. Physical barriers can be fixed by digging or drilling holes down through the compacted layer to a more permeable soil layer which will accept the salty water and move it away from the root zone. Backfill the holes with sand to help keep the hole from caving in and reconsolidating.
If sodium salt is a problem, water may stand for hours and sometime even days before it sinks in or evaporates away. The rule of thumb for managing sodium is this: If it takes more than one hour for water around a plant to sink in, treat for sodium.
Gypsum, available by the bag at most nurseries, is an ideal way to deal with sodium problems. Sprinkled on the surface of the ground and raked gently in before a deep irrigation, gypsum will replace the sodium in the soil with calcium. The deep irrigation then leaches the sodium out of the root zone.
Soil sulfur can also be used to eliminate sodium but it will only work if there is calcium or free lime already in the soil. Sulfur, moistened with water, becomes sulfuric acid which combines with the calcium to form gypsum. The process then proceeds as described above.
The coming warm weather months are a difficult time for plants, even those that are adapted to the extreme heat of the desert. Salt damage is one of the more common problems that gardeners must face during this time. By correctly managing irrigation water, most salt problems can be prevented.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Monday, July 15, 2013
Six Simple Soil Tests That You Can Do Yourself
You planted a tree, shrub, rosebush, or groundcover in your yard, and it died.
It was the healthiest plant you could find. You prepared the planting hole according to the best information available. You watered and fertilized it diligently. You were excited when it put out its first leaf of new growth; and, now you are devastated.
Never fun, and often expensive, dead and dying plants are no joking matter. There are many possible reasons, of course. A lack of water in the hot summer is deadly to plants. So also is too much water. It can lead to rotting roots.
In many cases, however, the causes of dead and dying plants can often be traced back to the soil itself. To be specific, there are five common soil problems that can, and often do lead to serious plant health issues.
Caliche is an accumulation of lime or as it is chemically known, calcium carbonate. It is a natural and common mineral in the desert and, in a refined form, is a basic component of concrete. Caliche can be found in the soil as small crumbs, thick or thin lenses, or solid sheets. It is grey in color and it is hard, very hard. If you have ever tried to dig through it, you will know what I mean.
Salinity, a buildup of naturally occurring salts in the soil, is also a common problem. Some salts, in beneficial amounts, are considered to be plant nutrients. Magnesium, zinc, and boron are examples. When these and other salt forming chemicals reach toxic levels in the soil, however, they can seriously injure or kill sensitive plants. We solve high salt concentration problems by leaching with extra water during an irrigation event to wash the salts down and out of the root zone.
The only exception to this rule is sodium. Sodium salt is a special case because it ties itself chemically to the individual soil particles and does not readily wash off during irrigations. Sodium in large amounts is especially toxic to plants.
Soils saturated with sodium take on unique characteristics. Because the alkali salt causes the soil particles to separate and act individually, the soil particles with the least disturbance can easily billow up into the air and create clouds of dust. Water often sits on the surface of these soils without sinking in until it evaporates. Sometimes the water will penetrate less than an inch into the soil. The soil also becomes quite sticky and readily clings to shoes, hands, and clothing. Gypsum, as an amendment, is the solution for sodium problems.
Another common problem is soil pH. Soil pH is a measure of the acidity or alkalinity of the soil. It is measured on a scale of 1 to 14 with 7 being neutral. A pH under 7 results in a progressively acid soil-water complex while a pH over seven is considered to be alkaline. A soil or water pH that is over 8.0 or under 6.5 can be toxic to plants, as well as inhibit the uptake of nutrients by the plant. Caliche and sodium are quite alkaline and are a leading cause of high pH soils in our area.
Soil compaction occurs when the soil is compressed by foot, animal, or vehicle traffic. Anyone who has noticed the lack of grass growing under a child’s swing set or in the ruts of a dirt road will understand the difficulty in growing plants in compacted soil.
Finally, desert soils are notoriously short of available nitrogen, an essential plant nutrient. Generally other nutrients like copper, potassium, and manganese are plentiful in our desert soils and we do not need to worry about feeding these nutrients when the plants are growing in native soils. Without regular applications of nitrogen, however, most non-native, introduced plants will not thrive.
So, how do we know if we have these soil problems in our yards? Here are six simple tests that anyone can do at home without having to be a soils expert or purchase a lot of expensive gadgets or materials.
Dig a hole. Using a pick and shovel, it is time to get a little exercise. Dig a hole right where you are thinking about planting a tree or shrub. The hole should be no deeper than the depth of the container and a little larger than it is wide. Your actual planting hole will be much wider, of course. Up to five times the diameter of the container in which the tree or shrub is planted is the recommendation, but loosening the soil for good root growth can come later. For now, let’s keep the size of the hole manageable.
The next step is to fill the hole with water and then time how long it takes for the water to sink into the ground, that is, to disappear. Most soils should drain within thirty minutes to one hour. Suspect caliche, sodium, or compaction problems if it takes longer. Do not plant anything at that site until you figure out and fix the problem. Drainage problems are a major cause of tree death in our area.
Shake a jar. Soil texture is a measure of sand, silt and clay in a soil. The more sand in the soil, the quicker a soil will drain. That is good. The more sand in a soil, the more frequently we have to irrigate. That can be bad.
Likewise, the more clay we have in a soil, the slower it drains. That can be bad. The more clay in a soil, the more water it will have available for plants. That can be good. A soil with a mixture of sand and clay is generally the best kind of soil for gardens and landscapes because it resists compaction and allows water to move easily through the soil profile.
To perform the test, fill a clear glass quart jar half full of soil. I like to take my samples about six inches deep. It avoids a lot of problems and gives me a good estimate of conditions in the root zone. Now, add water to the jar but do not fill it completely. There needs to be enough room for the water to slosh around. Filling the container up to the neck should be just fine. Seal the jar with a lid and shake it vigorously. Hint: do not do this over your expensive carpet. Sometimes the lid does not seal tightly with the rim of the jar.
Once the soil is totally mixed with the water, set the jar down and wait a few minutes. The sand in the soil will settle first, followed by silt and clay. A good garden soil will be about one half sand and one half silt and clay.
Probe for water. Using a soil probe, measure how deep the water penetrates the soil during an irrigation event. I like to use a long screwdriver. Where the soil is moist, the screwdriver will slip easily into the ground. When it hits dry soil, it will stop abruptly. With the probe in the ground, place your fingers at the soil level and remove the probe. Measure the distance between your fingers and the tip of the probe.
How deep should the water go? Use the”1-2-3 Rule”. Water small plants, such as ground covers, cacti, and annuals to a depth of one foot. Water medium plants such as shrubs to a depth of two feet. Large plants, such as trees, should be watered to a depth of three feet. Do not forget to soak the entire root zone. Most roots will fall inside a circle drawn at the edge of each plant’s canopy.
Lose a shoe? If you have a soil that resists water penetration and tends to pull the shoe off of your foot when you walk on it, think sodium. It is probably a good idea to treat the soil with an application of gypsum.
Watch for the fizz. Caliche is known to have a basic pH, that is, a pH well over the neutral point of 7 on the pH scale. Because of this, any acid coming in contact with the mineral will cause the caliche to bubble and fizz. Soil scientists use a drop of concentrated acid, like hydrochloric acid, placed onto soil sample to tell quickly and accurately whether caliche is present.
I personally do not like to carry concentrated acids with me because of the danger of caustic burns, so I use mild acids like vinegar, lemon, or lime juice. Because they are not strong acids, I have to look carefully to see the fizzing action, but they do work.
Leaves turn yellow? This is not specifically a soil test per se, but it is what we call in technical jargon, a bioassay. We use the plant itself to conduct the test. Look at the plant in question. If the older leaves down below the tip of the branch turn yellow while the new, upper leaves stay green, chances are you need to feed the plant with nitrogen during, or just before, the next irrigation. Ammonium sulfate, 21-0-0, is a good choice because the dissolved nitrogen will sink into the soil with water.
If the new leaves at the tips of the branches turn light green to yellow while the older leaves stay green, it may be an iron deficiency. Nitrogen and iron are the nutrients most commonly deficient, or unavailable, in desert soils.
We have listed the most common soil problems found in the desert and simple diagnostic tests that anyone can do. I hope that you will remember this basic rule of desert gardening: Problem soils can, and do, cause significant stress to garden and landscape plants. By knowing the more common soil problems and simple diagnostic tests that can be quickly done by the gardener, viable solutions to garden problems can be found.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
It was the healthiest plant you could find. You prepared the planting hole according to the best information available. You watered and fertilized it diligently. You were excited when it put out its first leaf of new growth; and, now you are devastated.
Never fun, and often expensive, dead and dying plants are no joking matter. There are many possible reasons, of course. A lack of water in the hot summer is deadly to plants. So also is too much water. It can lead to rotting roots.
In many cases, however, the causes of dead and dying plants can often be traced back to the soil itself. To be specific, there are five common soil problems that can, and often do lead to serious plant health issues.
Caliche is an accumulation of lime or as it is chemically known, calcium carbonate. It is a natural and common mineral in the desert and, in a refined form, is a basic component of concrete. Caliche can be found in the soil as small crumbs, thick or thin lenses, or solid sheets. It is grey in color and it is hard, very hard. If you have ever tried to dig through it, you will know what I mean.
Salinity, a buildup of naturally occurring salts in the soil, is also a common problem. Some salts, in beneficial amounts, are considered to be plant nutrients. Magnesium, zinc, and boron are examples. When these and other salt forming chemicals reach toxic levels in the soil, however, they can seriously injure or kill sensitive plants. We solve high salt concentration problems by leaching with extra water during an irrigation event to wash the salts down and out of the root zone.
The only exception to this rule is sodium. Sodium salt is a special case because it ties itself chemically to the individual soil particles and does not readily wash off during irrigations. Sodium in large amounts is especially toxic to plants.
Soils saturated with sodium take on unique characteristics. Because the alkali salt causes the soil particles to separate and act individually, the soil particles with the least disturbance can easily billow up into the air and create clouds of dust. Water often sits on the surface of these soils without sinking in until it evaporates. Sometimes the water will penetrate less than an inch into the soil. The soil also becomes quite sticky and readily clings to shoes, hands, and clothing. Gypsum, as an amendment, is the solution for sodium problems.
Another common problem is soil pH. Soil pH is a measure of the acidity or alkalinity of the soil. It is measured on a scale of 1 to 14 with 7 being neutral. A pH under 7 results in a progressively acid soil-water complex while a pH over seven is considered to be alkaline. A soil or water pH that is over 8.0 or under 6.5 can be toxic to plants, as well as inhibit the uptake of nutrients by the plant. Caliche and sodium are quite alkaline and are a leading cause of high pH soils in our area.
Soil compaction occurs when the soil is compressed by foot, animal, or vehicle traffic. Anyone who has noticed the lack of grass growing under a child’s swing set or in the ruts of a dirt road will understand the difficulty in growing plants in compacted soil.
Finally, desert soils are notoriously short of available nitrogen, an essential plant nutrient. Generally other nutrients like copper, potassium, and manganese are plentiful in our desert soils and we do not need to worry about feeding these nutrients when the plants are growing in native soils. Without regular applications of nitrogen, however, most non-native, introduced plants will not thrive.
So, how do we know if we have these soil problems in our yards? Here are six simple tests that anyone can do at home without having to be a soils expert or purchase a lot of expensive gadgets or materials.
Dig a hole. Using a pick and shovel, it is time to get a little exercise. Dig a hole right where you are thinking about planting a tree or shrub. The hole should be no deeper than the depth of the container and a little larger than it is wide. Your actual planting hole will be much wider, of course. Up to five times the diameter of the container in which the tree or shrub is planted is the recommendation, but loosening the soil for good root growth can come later. For now, let’s keep the size of the hole manageable.
The next step is to fill the hole with water and then time how long it takes for the water to sink into the ground, that is, to disappear. Most soils should drain within thirty minutes to one hour. Suspect caliche, sodium, or compaction problems if it takes longer. Do not plant anything at that site until you figure out and fix the problem. Drainage problems are a major cause of tree death in our area.
Shake a jar. Soil texture is a measure of sand, silt and clay in a soil. The more sand in the soil, the quicker a soil will drain. That is good. The more sand in a soil, the more frequently we have to irrigate. That can be bad.
Likewise, the more clay we have in a soil, the slower it drains. That can be bad. The more clay in a soil, the more water it will have available for plants. That can be good. A soil with a mixture of sand and clay is generally the best kind of soil for gardens and landscapes because it resists compaction and allows water to move easily through the soil profile.
To perform the test, fill a clear glass quart jar half full of soil. I like to take my samples about six inches deep. It avoids a lot of problems and gives me a good estimate of conditions in the root zone. Now, add water to the jar but do not fill it completely. There needs to be enough room for the water to slosh around. Filling the container up to the neck should be just fine. Seal the jar with a lid and shake it vigorously. Hint: do not do this over your expensive carpet. Sometimes the lid does not seal tightly with the rim of the jar.
Once the soil is totally mixed with the water, set the jar down and wait a few minutes. The sand in the soil will settle first, followed by silt and clay. A good garden soil will be about one half sand and one half silt and clay.
Probe for water. Using a soil probe, measure how deep the water penetrates the soil during an irrigation event. I like to use a long screwdriver. Where the soil is moist, the screwdriver will slip easily into the ground. When it hits dry soil, it will stop abruptly. With the probe in the ground, place your fingers at the soil level and remove the probe. Measure the distance between your fingers and the tip of the probe.
How deep should the water go? Use the”1-2-3 Rule”. Water small plants, such as ground covers, cacti, and annuals to a depth of one foot. Water medium plants such as shrubs to a depth of two feet. Large plants, such as trees, should be watered to a depth of three feet. Do not forget to soak the entire root zone. Most roots will fall inside a circle drawn at the edge of each plant’s canopy.
Lose a shoe? If you have a soil that resists water penetration and tends to pull the shoe off of your foot when you walk on it, think sodium. It is probably a good idea to treat the soil with an application of gypsum.
Watch for the fizz. Caliche is known to have a basic pH, that is, a pH well over the neutral point of 7 on the pH scale. Because of this, any acid coming in contact with the mineral will cause the caliche to bubble and fizz. Soil scientists use a drop of concentrated acid, like hydrochloric acid, placed onto soil sample to tell quickly and accurately whether caliche is present.
I personally do not like to carry concentrated acids with me because of the danger of caustic burns, so I use mild acids like vinegar, lemon, or lime juice. Because they are not strong acids, I have to look carefully to see the fizzing action, but they do work.
Leaves turn yellow? This is not specifically a soil test per se, but it is what we call in technical jargon, a bioassay. We use the plant itself to conduct the test. Look at the plant in question. If the older leaves down below the tip of the branch turn yellow while the new, upper leaves stay green, chances are you need to feed the plant with nitrogen during, or just before, the next irrigation. Ammonium sulfate, 21-0-0, is a good choice because the dissolved nitrogen will sink into the soil with water.
If the new leaves at the tips of the branches turn light green to yellow while the older leaves stay green, it may be an iron deficiency. Nitrogen and iron are the nutrients most commonly deficient, or unavailable, in desert soils.
We have listed the most common soil problems found in the desert and simple diagnostic tests that anyone can do. I hope that you will remember this basic rule of desert gardening: Problem soils can, and do, cause significant stress to garden and landscape plants. By knowing the more common soil problems and simple diagnostic tests that can be quickly done by the gardener, viable solutions to garden problems can be found.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Friday, July 12, 2013
Scarey Arachnids of the Desert
Four desert arachnids, all spider relatives, create feelings of concern and even fear in the hearts and minds of those who come in contact with them. Two of them, the black widow spider and Arizona brown spider, are well deserving of respect. The other two are actually quite harmless; only their appearance gives them a hard reputation. Here are some answers to commonly asked questions about these interesting animals.
Black Widow Spiders. The adult black widow spider female is colored glossy-black with a bright orange to red hourglass-shaped marking on the underside of the abdomen. The body of the female is about ½ inch long and, with legs extended, may be up to 2 inches long. The males also have the red hourglass on the underside of their abdomen, but are cream and tan in color and much smaller in size. Newly hatched black widows are white with black spots on their abdomen with a cream-colored hourglass. Later, as they mature, they become cream and brown-striped. All stages of both sexes are venomous. Even the egg sacs contain poison, and should be carefully removed and crushed.
Black widow webs are irregularly shaped with strands running in many directions. The somewhat stiff webs are said to appear “messy”, meaning that they have no particular pattern. The spiders hide during the day, and hang upside down in their webs at night. When mature, the female mates and lays several hundred eggs. She then wraps the eggs in a silken cocoon called the “egg sac”. Female black widows guard the sac until the eggs hatch. During this time she is most likely to bite when threatened. Egg sacs are most frequently encountered from May to October.
Black widow spiders do not aggressively hunt humans, but will bite to defend themselves. Be cautious when picking up or moving objects, particularly in outbuildings such as sheds or garages, or in shady, undisturbed areas such as under parked cars or in flower pots. Although they are not commonly found indoors, it is always a good idea to shake out and check clothing before dressing.
Black widow venom is a nerve toxin, which means that as it acts on the nervous system, it causes progressive muscle pain and can sometimes cause difficulty in breathing. The initial bite has been described as anywhere between a pin prick and a sharp stabbing pain, but some people do not even realize that they have been bitten. Although bites are generally not fatal, they should be considered dangerous. Contact the local Poison Control Center immediately for information about treatment and care if someone is bitten.
Sun Spiders. Sun spiders may be up the three inches long, and are usually tan or light brown in color. Although they are not scorpions, sun spiders are sometimes called windscorpions because they can move very quickly. Scientists call them solpugids, which is based on their scientific name.
Although they may appear grotesque to someone who has never seen one before, they are relatively harmless. Sun spiders have the ability to bite, but it is more like a pinch and they have little or no venom. They do not have a stinger so they can not sting. In fact, sun spiders can be considered to be beneficial because they eat pest insects. Because sun spiders do not pose a health risk to humans, they do not require chemical control.
Sun spiders are common residents of hot, arid regions. Over one hundred species are found here in the Southwest. They hide under rocks and stones during the day and hunt for insects and other invertebrates at night. They often come to outdoor lights to feed on the insects the lights attract.
Occasionally sun spiders may enter homes where they might become a nuisance. Most can be captured, then removed to the outdoors and set free. Sun spiders which find their way inside and, for one reason or another must be killed, are easily dispatched with a vacuum cleaner or fly swatter. To discourage sun spiders from coming indoors, turn off outdoor lights as much as possible. Make sure screens and doors fit snugly, and fill or cover all cracks or holes in exterior walls and foundations.
Arizona Brown Spiders. Arizona brown spiders are often mistaken for the brown recluse spider, which is not a normal resident of Arizona. The only brown recluse spiders found here are the ones who have been brought into the state in luggage or belongings of persons who recently come from regions where it does occur. This hitch hiking, fortunately, does not happen frequently. However, because these spiders are so closely related and because the venom of each causes similar symptoms, they are often treated, and feared, as one in the same.
The two species of brown spiders in Arizona closely resembling the brown recluse spider have a dark brown marking on the front portion of their body which resembles a lyre or violin. They appear two-toned, with a tan front and gray rear body region. These spiders have three pairs of eyes in a crescent shape across the top, rather than the four pairs of most other spiders. Arizona brown spiders are small. Including legs, their total size is only about the area of a nickel. The body region of adults is one-third inch long.
Arizona brown spiders normally nest in protected areas, such as under wood or dead cacti in the desert, their native habitat. They can be found in urban areas, but it usually is because they have been brought in from the desert on firewood or pieces of cactus skeleton acquired for landscape purposes. They build a loose web of white silk where they stay during the daylight hours. As with the black widow, Arizona brown spiders are active at night.
Once again, these spiders are normally quite timid and only bite when trapped. Persons bitten apparently at first feel no discomfort, but as time progresses a blister forms, which may become an open ulcer. Other symptoms include fever and nausea. Persons bitten should make every attempt to capture the spider for identification and call the local Poison Control Center immediately.
Tarantulas. Tarantulas are the largest spider found in this region, up to six inches in diameter. They are hairy and are often black with red markings.
Despite their large size, tarantulas are not aggressive, and they rarely bite. If they are harassed into biting, the bite is not considered dangerous. There is little lasting pain or subsequent serious health problems. However, as with many other biting and stinging creatures, if an individual is allergic to the venom, they may have a more serious reaction and should seek medical attention immediately.
Believe it or not, the tarantulas’ hairs can be more harmful than their bite. When threatened, tarantulas stroke the back of their abdomen with their hind legs and “kick” off fine, barbed hairs. These hairs introduce a toxin into the skin that can cause burning and itching, and may result in a serious skin rash.
While it is true that some Arizona spiders are truly venomous, there are many more that either have no venom or are not a serious threat to humans. By being aware of which are and which are not a credible threat, we can learn to enjoy the desert creatures and protect ourselves as well.
If you have questions, you can reach one of our Master Gardener volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Black Widow Spiders. The adult black widow spider female is colored glossy-black with a bright orange to red hourglass-shaped marking on the underside of the abdomen. The body of the female is about ½ inch long and, with legs extended, may be up to 2 inches long. The males also have the red hourglass on the underside of their abdomen, but are cream and tan in color and much smaller in size. Newly hatched black widows are white with black spots on their abdomen with a cream-colored hourglass. Later, as they mature, they become cream and brown-striped. All stages of both sexes are venomous. Even the egg sacs contain poison, and should be carefully removed and crushed.
Black widow webs are irregularly shaped with strands running in many directions. The somewhat stiff webs are said to appear “messy”, meaning that they have no particular pattern. The spiders hide during the day, and hang upside down in their webs at night. When mature, the female mates and lays several hundred eggs. She then wraps the eggs in a silken cocoon called the “egg sac”. Female black widows guard the sac until the eggs hatch. During this time she is most likely to bite when threatened. Egg sacs are most frequently encountered from May to October.
Black widow spiders do not aggressively hunt humans, but will bite to defend themselves. Be cautious when picking up or moving objects, particularly in outbuildings such as sheds or garages, or in shady, undisturbed areas such as under parked cars or in flower pots. Although they are not commonly found indoors, it is always a good idea to shake out and check clothing before dressing.
Black widow venom is a nerve toxin, which means that as it acts on the nervous system, it causes progressive muscle pain and can sometimes cause difficulty in breathing. The initial bite has been described as anywhere between a pin prick and a sharp stabbing pain, but some people do not even realize that they have been bitten. Although bites are generally not fatal, they should be considered dangerous. Contact the local Poison Control Center immediately for information about treatment and care if someone is bitten.
Sun Spiders. Sun spiders may be up the three inches long, and are usually tan or light brown in color. Although they are not scorpions, sun spiders are sometimes called windscorpions because they can move very quickly. Scientists call them solpugids, which is based on their scientific name.
Although they may appear grotesque to someone who has never seen one before, they are relatively harmless. Sun spiders have the ability to bite, but it is more like a pinch and they have little or no venom. They do not have a stinger so they can not sting. In fact, sun spiders can be considered to be beneficial because they eat pest insects. Because sun spiders do not pose a health risk to humans, they do not require chemical control.
Sun spiders are common residents of hot, arid regions. Over one hundred species are found here in the Southwest. They hide under rocks and stones during the day and hunt for insects and other invertebrates at night. They often come to outdoor lights to feed on the insects the lights attract.
Occasionally sun spiders may enter homes where they might become a nuisance. Most can be captured, then removed to the outdoors and set free. Sun spiders which find their way inside and, for one reason or another must be killed, are easily dispatched with a vacuum cleaner or fly swatter. To discourage sun spiders from coming indoors, turn off outdoor lights as much as possible. Make sure screens and doors fit snugly, and fill or cover all cracks or holes in exterior walls and foundations.
Arizona Brown Spiders. Arizona brown spiders are often mistaken for the brown recluse spider, which is not a normal resident of Arizona. The only brown recluse spiders found here are the ones who have been brought into the state in luggage or belongings of persons who recently come from regions where it does occur. This hitch hiking, fortunately, does not happen frequently. However, because these spiders are so closely related and because the venom of each causes similar symptoms, they are often treated, and feared, as one in the same.
The two species of brown spiders in Arizona closely resembling the brown recluse spider have a dark brown marking on the front portion of their body which resembles a lyre or violin. They appear two-toned, with a tan front and gray rear body region. These spiders have three pairs of eyes in a crescent shape across the top, rather than the four pairs of most other spiders. Arizona brown spiders are small. Including legs, their total size is only about the area of a nickel. The body region of adults is one-third inch long.
Arizona brown spiders normally nest in protected areas, such as under wood or dead cacti in the desert, their native habitat. They can be found in urban areas, but it usually is because they have been brought in from the desert on firewood or pieces of cactus skeleton acquired for landscape purposes. They build a loose web of white silk where they stay during the daylight hours. As with the black widow, Arizona brown spiders are active at night.
Once again, these spiders are normally quite timid and only bite when trapped. Persons bitten apparently at first feel no discomfort, but as time progresses a blister forms, which may become an open ulcer. Other symptoms include fever and nausea. Persons bitten should make every attempt to capture the spider for identification and call the local Poison Control Center immediately.
Tarantulas. Tarantulas are the largest spider found in this region, up to six inches in diameter. They are hairy and are often black with red markings.
Despite their large size, tarantulas are not aggressive, and they rarely bite. If they are harassed into biting, the bite is not considered dangerous. There is little lasting pain or subsequent serious health problems. However, as with many other biting and stinging creatures, if an individual is allergic to the venom, they may have a more serious reaction and should seek medical attention immediately.
Believe it or not, the tarantulas’ hairs can be more harmful than their bite. When threatened, tarantulas stroke the back of their abdomen with their hind legs and “kick” off fine, barbed hairs. These hairs introduce a toxin into the skin that can cause burning and itching, and may result in a serious skin rash.
While it is true that some Arizona spiders are truly venomous, there are many more that either have no venom or are not a serious threat to humans. By being aware of which are and which are not a credible threat, we can learn to enjoy the desert creatures and protect ourselves as well.
If you have questions, you can reach one of our Master Gardener volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221, extension 204. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85122
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Monday, July 1, 2013
Preparing for Hot Weather Plant Stress
Summer temperatures are here! How are your plants doing?
Every year a large number of local trees, shrubs and other plants are heavily damaged from the heat and dryness of the summer months. Arizona’s hot, dry summers are tough on plants, especially on non-native trees and shrubs that are not particularly adapted to desert conditions. Even native trees and shrubs, if they are not properly cared for, can be injured by the desert heat. There is hope, however. Proper planning coupled with good plant care can go a long ways in preventing much of the damage. Here are a few suggestions to help protect plants from hot weather injury.
First, the best defense against heat injury is a healthy, actively growing plant. In this climate, proper watering is an absolute key to maintaining the health of trees and shrubs during the summer.
Most water absorbed by plant roots is used for transpiration, the loss of water vapor through the leaves. At the end of its trip through the plant, water enters open spaces between the cells of the leaves where it evaporates and exits the plant through tiny holes in the leaf called stomata. This movement of water vapor out of the plant acts much like an evaporative cooler by removing excess heat and leaving the leaf tissue cool to the touch. Supplying enough water to keep the transpiration process going is a critical step in protecting landscape plants in the desert. Insufficient water at any time during the growing season can seriously damage plants.
To make sure that plants receive enough water, irrigate properly. Schedule irrigations frequently enough to maintain sufficient water for the plant at all times, but infrequently enough to let air return to the soil and give roots a breath of fresh air. It is especially critical that regular, deep irrigations begin when the thermometer approaches 100 degrees F. on a regular basis.
All roots require both water and air to properly function. During the summer months, trees and shrubs should be flood irrigated with the hose every 5 to 10 days depending upon their water use needs. High water users like mulberries and ash trees may need to be watered more frequently than those with moderate requirements like citrus or low water requirements like mesquite and palo verde. With a drip system, irrigations will have to occur more frequently, perhaps every other day or so depending upon the type of emitters used.
The best way to determine irrigation frequency, which is influenced by the temperature, type of soil and the evaporation rate of water from the soil surface, is to dig down about six inches into the ground and pick up a handful of soil. If the soil remains in a hard ball after it has been squeezed, it probably is still moist enough to support plant growth. If, however, the ball begins to crumble when the hand is opened or if the soil is starting to feel dry, it is time to water. With this simple test, anyone can properly determine the correct irrigation frequency for the specific conditions in their own yard. Don’t forget that the irrigation frequency that supports proper plant growth in the winter and spring will probably not be sufficient in the summer when temperatures go up dramatically.
Make sure that the water applied to the plant wets the entire area from the trunk or stem out to at least, and perhaps beyond, the drip line of the plant. Adding enough water to move the lower edge of the wetted zone deep enough to reach the lower roots is also critical.
Fertilizing during hot weather should be done cautiously. The increased activity of life processes during the warm months can use up nutrient reserves faster, but a too-rapid uptake of fertilizers by summer-active roots could result in fertilizer burn. A good rule of thumb for fertilizing during the hot season is to increase the fertilization frequency, but decrease the amount of fertilizer applied each time. Fall fertilization helps plants recover from summer exhaustion, while spring fertilization helps encourage strong growth to better withstand summer stress.
Second, protect the roots of heat sensitive plants by mulching the surface of the soil with an organic mulch. Mulch spread over soil surfaces under plants provides a practical insulation against summer heat. Mulches also reduce evaporation of water from the surface of the soil. Not only does this contribute to a more efficient use of water resources, but it also helps minimize the buildup of toxic salts at the soil surface.
Mulching can pose a danger, however. Since surface mulches retain soil moisture longer, the intervals between irrigations must be lengthened to ensure the proper balance of water and air in the soil. If not, over watering problems like root rot and iron chlorosis could occur. These problems could seriously damage the health of the tree. Again, the hand feel method of testing soil moisture levels is a great way to help determine the timing of irrigations.
Finally, avoid the temptation to use drainage water from evaporative coolers and swimming pools as well as water that has been through a water softening system. Each of these water sources carry excessive salts that could damage tender plants.
Protection of plants from summer injury generally boils down to proper irrigation and fertilization. Just a little extra care now can save serious injury later on.
For more information on how to protect trees and shrubs from summer injury, ask for a copy of the Cooperative Extension leaflet, “Hot Weather Effects on Landscape Plants”. If you have questions, you can reach Rick Gibson or one of the Master Gardener Volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85222
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
Every year a large number of local trees, shrubs and other plants are heavily damaged from the heat and dryness of the summer months. Arizona’s hot, dry summers are tough on plants, especially on non-native trees and shrubs that are not particularly adapted to desert conditions. Even native trees and shrubs, if they are not properly cared for, can be injured by the desert heat. There is hope, however. Proper planning coupled with good plant care can go a long ways in preventing much of the damage. Here are a few suggestions to help protect plants from hot weather injury.
First, the best defense against heat injury is a healthy, actively growing plant. In this climate, proper watering is an absolute key to maintaining the health of trees and shrubs during the summer.
Most water absorbed by plant roots is used for transpiration, the loss of water vapor through the leaves. At the end of its trip through the plant, water enters open spaces between the cells of the leaves where it evaporates and exits the plant through tiny holes in the leaf called stomata. This movement of water vapor out of the plant acts much like an evaporative cooler by removing excess heat and leaving the leaf tissue cool to the touch. Supplying enough water to keep the transpiration process going is a critical step in protecting landscape plants in the desert. Insufficient water at any time during the growing season can seriously damage plants.
To make sure that plants receive enough water, irrigate properly. Schedule irrigations frequently enough to maintain sufficient water for the plant at all times, but infrequently enough to let air return to the soil and give roots a breath of fresh air. It is especially critical that regular, deep irrigations begin when the thermometer approaches 100 degrees F. on a regular basis.
All roots require both water and air to properly function. During the summer months, trees and shrubs should be flood irrigated with the hose every 5 to 10 days depending upon their water use needs. High water users like mulberries and ash trees may need to be watered more frequently than those with moderate requirements like citrus or low water requirements like mesquite and palo verde. With a drip system, irrigations will have to occur more frequently, perhaps every other day or so depending upon the type of emitters used.
The best way to determine irrigation frequency, which is influenced by the temperature, type of soil and the evaporation rate of water from the soil surface, is to dig down about six inches into the ground and pick up a handful of soil. If the soil remains in a hard ball after it has been squeezed, it probably is still moist enough to support plant growth. If, however, the ball begins to crumble when the hand is opened or if the soil is starting to feel dry, it is time to water. With this simple test, anyone can properly determine the correct irrigation frequency for the specific conditions in their own yard. Don’t forget that the irrigation frequency that supports proper plant growth in the winter and spring will probably not be sufficient in the summer when temperatures go up dramatically.
Make sure that the water applied to the plant wets the entire area from the trunk or stem out to at least, and perhaps beyond, the drip line of the plant. Adding enough water to move the lower edge of the wetted zone deep enough to reach the lower roots is also critical.
Fertilizing during hot weather should be done cautiously. The increased activity of life processes during the warm months can use up nutrient reserves faster, but a too-rapid uptake of fertilizers by summer-active roots could result in fertilizer burn. A good rule of thumb for fertilizing during the hot season is to increase the fertilization frequency, but decrease the amount of fertilizer applied each time. Fall fertilization helps plants recover from summer exhaustion, while spring fertilization helps encourage strong growth to better withstand summer stress.
Second, protect the roots of heat sensitive plants by mulching the surface of the soil with an organic mulch. Mulch spread over soil surfaces under plants provides a practical insulation against summer heat. Mulches also reduce evaporation of water from the surface of the soil. Not only does this contribute to a more efficient use of water resources, but it also helps minimize the buildup of toxic salts at the soil surface.
Mulching can pose a danger, however. Since surface mulches retain soil moisture longer, the intervals between irrigations must be lengthened to ensure the proper balance of water and air in the soil. If not, over watering problems like root rot and iron chlorosis could occur. These problems could seriously damage the health of the tree. Again, the hand feel method of testing soil moisture levels is a great way to help determine the timing of irrigations.
Finally, avoid the temptation to use drainage water from evaporative coolers and swimming pools as well as water that has been through a water softening system. Each of these water sources carry excessive salts that could damage tender plants.
Protection of plants from summer injury generally boils down to proper irrigation and fertilization. Just a little extra care now can save serious injury later on.
For more information on how to protect trees and shrubs from summer injury, ask for a copy of the Cooperative Extension leaflet, “Hot Weather Effects on Landscape Plants”. If you have questions, you can reach Rick Gibson or one of the Master Gardener Volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85222
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
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