It is an all too common scenario in the landscape, but a discerning eye can pick it up and get it right just about every time.
The scenario goes something like this. There are several trees, usually close together, planted just about the same time in just about the same way. Every tree but one is doing just fine. They all have green leaves and are growing well. The one that is doing poorly is stunted and displays yellow leaves that die back far too soon. Sound familiar? Unfortunately in the desert, this is a very common complaint.
Stunted, stressed plants in the midst of neighbors planted at the same time and treated in the same way usually is a dead giveaway that there is a layer of caliche below the surface of the soil. It is a silent, invisible troublemaker that can cause real problems. In most cases, you will never know it is there until the plants start screaming for help.
Caliche is usually a cemented soil layer containing large amounts of calcium carbonate, or lime. It binds sand and gravel together so hard and tight that roots and water have a difficult time getting through. It is light in color and it is difficult to dig through. Anyone who has tried to dig through caliche will never forget the experience. The clincher in identifying caliche is to sprinkle a few drops of vinegar or some other acid onto the surface of the layer. If it is caliche, it will fizz or bubble as soon as the drops hit the caliche.
Caliche does not necessarily have to be in layers. It can also be found in lumps or even granules within the soil. The vinegar test is the best way to tell for sure if it is there. Caliche can be close to the surface of the soil, on top of the soil or far below. It can run anywhere from a few inches to many feet thick. There can even be more than one layer!
Iron chlorosis is one of the common problems of plants in or near caliche. The pH of the soil is high enough to cause iron to become unavailable to the plants. The usual symptoms are yellowing, dark veins, and untimely leaf drop.
A second problem is the lack of water and root penetration. Even if the layer is loose, roots may still not penetrate.
A third problem is drainage. The soil must be allowed to drain to insure adequate levels of oxygen for root growth. A yellowing or type of chlorosis may be seen if the root zone does not have enough oxygen. Overwatering can also cause a similar yellow symptom.
The best way to avoid damage to plants from caliche is to try to keep plant roots out of the caliche zone. Obviously, this is easier said than done. One way to do this is to dig the tree or shrub hole early and test for drainage by filling the hole with water and seeing how long it takes to empty. If the water level drops four inches or more in four hours, caliche is probably not present and the drainage should be all right.
If caliche is present, if possible, remove the caliche and replace it with soil similar to that which is in the area before planting. Do not try to reclaim the caliche with soil amendments. Unless there is just a small amount of caliche present, acid soil amendments, organic matter and other treatments will work so slowly that it may take years to see any difference. Just dig it out and get rid of it.
The planting hole is also important in managing caliche. It should be large enough to accommodate the root system of mature trees and shrubs. This means that the planting hole should be up to five times the diameter of the container in which the new plant comes from the nursery. The hole need not be deep, because most desert-adapted trees and shrubs, like mesquite and Cassia, are relatively shallow rooted under normal landscape conditions. In all cases, however, the hole, or at least a small chimney, must extend down through the caliche layer to avoid drainage and resulting salinity problems.
If it is not possible to dig down through the caliche layer and remove it, then it will be important to avoid it. Choose another location that is free from caliche, or construct a raised bed to elevate the plants above the caliche layer sufficiently high to provide good drainage. Someone I know had to deal with an extremely thick caliche layer that was close to the soil. He solved the problem by purchasing railroad ties and stacking them up to waist high and then filling the new box with planting soil. Into this construction he planted full-sized citrus trees which flourished in a spot where otherwise they would have struggled.
Caliche is very common throughout Pinal County in desert soils. If we can find a way around or through a caliche layer so that salts and excess water can drain through to a more absorbent layer of soil below, in many cases affected plants will quickly recover and catch up with their neighbors.
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
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