The following information is from the Arizona Master Gardener Manual, which is compiled and published by University of Arizona Cooperative Extension.
The "Big House" in Casa Grande, Arizona was made by the Hohokam people from dried mud mixed with caliche, the calcium carbonate content of which makes it harden into a simple type of concrete.
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What is Caliche?
Caliche is soil that is cemented together by lime (calcium carbonate). Caliche usually is found as a light-colored layer in the soil or as white or cream-colored concretions, or lumps, mixed with the soil. Layers vary in thickness from a few inches to several feet. Many southern Arizona soils have layers of caliche.
What does caliche do to plants?
Caliche causes three problems in the yard or garden.
The layer can be so solid that roots cannot penetrate. The result is that plants have only the soil above the caliche as a source of nutrients, and water and root development is restricted.
Caliche can reduce water movement. The restricted water penetration can contribute to inadequate root aeration and accumulation of salt. Both problems reduce the vigor of growing plants.
The pH and free calcium carbonate in a caliche are often high enough to cause iron to become unavailable for plants. The symptoms of iron deficiency are a yellowing of the youngest leaves while the veins in the leaves remain green. The resulting striping appearance is different from that of nitrogen deficiency symptoms, which are a general yellowing including the veins of older leaves. Iron deficiencies are additionally aggravated by the water saturation of the soil.
How can caliche be managed?
Successful home and horticultural plantings can be made by first removing caliche and replacing it with a soil mix. The hole for planting should be large enough to accommodate the root zone system of the mature plant. It should be dug completely through the caliche layer so that water will drain from the planting hole. If it is not practical to dig completely through the caliche zone, then dig a smaller drainage hole through the caliche.
Check the planting hole for drainage before adding plants or soil. Partially fill the hole with water. If the water level drops 4 inches or more in four hours, the drainage should be adequate. Discard the caliche that has been removed. Keep the consistency of the soil mix the same throughout the planting hole and drainage chimney. If a lawn is to be grown over caliche, provide at least 8 inches of good topsoil above the caliche.
Problems with caliche
- Restriction of root penetration and root development
- Restriction of water penetration, resulting in poor root aeration and salt accumulation
- Causing iron to become unavailable to the plants
Strategies
- If possible, remove caliche before planting. Make planting holes large enough for a mature root system.
- Before planting, make certain water drains from the planting hole.
- Replace caliche with good topsoil or a soil mix. Discard the caliche.
- Lawns should be grown only where at least 8 inches of topsoil exists above the caliche.