Friday, June 14, 2013

Growing Cacti in Raised Beds

Growing Cacti in Raised Beds

Rick Gibson
Cooperative Extension Agent, Agriculture
Pinal County, Arizona

If you would like to enjoy the colors and textures brought by the many species of cacti but dread the spines, consider a raised bed garden for these prickly plants.

A cactus garden can be a wonderful way to enjoy the colors and textures of cacti in the home landscape, but working around the plants, especially prickly pear and cholla, can be a painful experience.  A raised bed cactus garden is a good way to keep hands, arms and feet away from the spines and still experience the many beautiful species of cacti that will grow in this area. 

The familiar saguaro, barrel, hedgehog, Mammillaria, prickly pear and cholla cacti are all native to the Sonoran Desert and are well adapted for landscape use in our area.  Their presence in a landscape can give that authentic touch of native dignity that seems to legitimize and complement Arizona desert landscapes.

In addition to the native species, there are many non-native species that also do well in the desert environment.  Compass barrel cactus, Ferocactus cylindraceus, and the“old man cactus”, Cephalocerus senilis, are examples of species from other areas.  A landscape decorated with a mix of these exotic cacti and species from our own Sonoran Desert can be quite interesting and unique.

Because of the way that they are built, and the way that they carry out their life processes, cacti are well adapted to desert living and make good low water use plants.  The thick, wax-coated stems of cacti, for example, are quite resistant to moisture evaporation.  This ability to protect themselves from significant water loss through their tissues gives them considerable drought tolerance.

Cacti are leafless, but almost all of them have modified stems called spines.  These spines can be straight and needle sharp, such as in the hedgehogs, or curved and broadly pointed like the barrel.  These modified stems give a measure of protection from the feeding of animals that might be looking for a source of water.  They can also cause a painful experience if one gets too close.

The prickly pear and cholla species have the straight defensive spines, but these particular cacti are especially painful because they have a second type of spine.  These tiny spines, called glochids, are hair-like whiskers with barbed structures on their surfaces.  Almost invisible to the eye, they can be quite painful and troublesome.  Many who have experienced these tiny spines have come to appreciate the value of sticky tape and tweezers as they have struggled to remove them from their skin.

It is the presence of spines, especially these glochids, that lead many to shy away from planting cacti in the landscape.  A misstep off the path in a cactus garden can lead to a painful encounter with cacti.  Dragging hoses to water other landscape plants almost always results in spines becoming attached to the hose.  Invariably, these spines will be transferred from the hose to the hands, arms, and legs of whoever might later be coiling the hose for storage. 

One way to help prevent these types of encounters and to help keep the proper distance between people and plants is to place the cacti in raised beds.  The framework that creates the raised bed  will automatically set the limits between space set aside for people and space that is set aside for cacti.  The raised bed sends a strong message to all: venture beyond at your own risk. 

Besides physically limiting the possibility of people and pets to move into the garden space, the raised bed structure itself creates a barrier that will prevent a hose from being dragged into the cacti and serves as a boundary limit that will protect wheel barrows, electrical cords and other garden tools from coming in contact with the spines.  It provides an extra layer of safety.

The raised bed garden also makes an ideal showcase for viewing the cacti.  By locating the cacti closer to eye level, it places them in a position where their good points can be more easily seen. 

To create a raised bed for cacti, consider using railroad ties placed side by side and end down to create a strong barrier.  The ties should be buried about eighteen inches deep into the soil to prevent the weight of the soil inside the bed from pushing out the framework.  The height of the bed can vary but probably should not be taller than twenty-four inches or less than twelve.  The framework for the bed can be built square for a formal look, or with softened corners for a more natural feel. 

Other materials can be used for a raised bed.  Decorative or standard concrete blocks, lumber or even old, worn out tires can be painted and stacked in various arrangements to provide an interesting, but effective arrangement.

Soil used inside the garden should drain well.  For this reason, it is recommended that soils should contain large amounts of sand.  Place the soil in mounds and plant the cacti at the peak of the mound so that water will drain away from the base of the plant.  Water accumulating around these plants can cause the base to rot and eventually lead to the death of the plant.

Weeds can cause a huge problem for those working in cactus gardens.  Weeds growing in close proximity to spines will be difficult to remove by hand.  Locate the garden well away from Bermuda grass lawns to prevent the invasion of this tough weed, and make sure the soil inside the garden is free of nutsedge tubers and other perennial weeds. 

Most weeds in a cactus garden can be prevented by placing a one to two inch layer of rock mulch around the plant.  Larger rock, such as 1.5 inch leach rock, makes the best mulch, but other sizes and colors will also work.  The use of plastic on the surface of the soil under the rock mulch is not recommended.  It prevents surface water from sinking into the root zone and with each passing dust storm supports the accumulation of an artificial zone of soil on top of the plastic in which weed seeds can germinate.

With a little time, energy and know how, a raised bed garden will define the safe boundary between people and cacti and, at the same time, show off the various species in an attractive way.

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.  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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