A guide to caliche soil, how it harms plants, and how to manage it so you can successfully grow trees and other plants in your Phoenix area yard.
Caliche, an accumulation of calcium carbonate found in the ground throughout Southern Arizona, can be frustrating to deal with when you are trying to add new plants or trees to your property. The rock-like soil can be nearly impossible to dig through and has ruined many gardening tools, not to mention killed many plants that couldn’t survive in caliche-filled soil.
In this article, we share the facts about caliche, explain how it affects plants (and planting), and give you our best tips for how to deal with it. Even if your property is filled with caliche, you CAN plant trees, shrubs, and other plants!
What is caliche?
Caliche is part of the soil composition in our part of Arizona, including in Phoenix and Anthem. It is a layer of soil in which the particles have become compacted together with calcium carbonate to form a dense, concrete-like substance. This layer can be less than an inch thick to up to 3 feet! If you encounter caliche when digging, it can seem like you’re trying to dig through concrete.
Other names for caliche include calcrete, hardpan, duricrust, and calcic soil. But whatever name it goes by, you’ll know it’s there because the soil becomes rock-hard and nonporous.
Soil with a thick layer of clay or limestone is sometimes also referred to as caliche, but it’s not the same thing. It can, however, have some of the same issues.
Where is caliche found?
Caliche forms in areas that don’t receive a lot of rainfall (less than 26 inches a year) and where the mean annual temperature is above 41 degrees Fahrenheit. This includes the Sonoran, Chihuahuan, and Mojave Deserts, parts of Australia, Eastern Saudi Arabia, and the Kalahari Desert in Africa. Caliche is also found with mineral deposits in northern Chile and Peru.
What does caliche look like?
Caliche resembles a light-colored rock and ranges in color from white or gray to brown or red. It is usually found close to the surface although there can be several layers of caliche in one location. It’s often difficult to pinpoint exactly where caliche will form; it’s often found scattered throughout an area.
How does caliche form?
Caliche is a natural substance formed when calcium is added to the soil, usually from rainwater. When combined with the carbon dioxide in the soil, calcium carbonate is formed. This is a fairly slow process, and it takes time for caliche deposits to build up. That’s why caliche is usually found in undisturbed soils, such as those found in the desert.
How does caliche impact planting and gardening?
If you find caliche on your property, you will have a difficult time creating a planting hole. It’s not called a “natural cement” for no reason!
Caliche in the soil can become a problem for plants as the roots try to grow outward, causing the roots to be restricted to a small area. When a tree is planted in these conditions, the roots are not able to anchor the tree, making it more likely to tip or fall over.
>> Learn other reasons why your tree may fall in our article on why trees fall over.
Because water doesn’t drain through caliche, it can cause salt buildup in the soil. (We previously wrote about how to recognize the signs of salt buildup in desert soil.) The lack of drainage also means that plants can “drown” from lack of oxygen in the soil and/or their roots can rot from excess water.
Depending on where it’s located, caliche can also do the opposite - prevent water from reaching the roots of a plant or tree.
Plus, because it has a high pH, caliche can cause iron deficiency in plants. This iron deficiency will show up as yellow or white leaves. Other micronutrients, such as phosphorous, boron, and manganese can become deficient as well.
What can property owners do about caliche?
There are several actions you can take to reduce the impact of caliche in your landscape.
Break Caliche Up and/or Remove It
When planting, break up and remove as much caliche as possible. This can be a long, tedious, and physically demanding job, so you may need to hire someone to do this task for you.
In many cases, a jackhammer may be needed to break up the caliche to remove it. Other tools you can try using include:
- Rock bar
- Drill with a masonry bit
Of course, what tool you use to break up or remove the caliche is dependent on how much you have and how thick the layer is. Using a tiller on a 3-foot-thick section, for example, would probably ruin your machine and have little impact on the caliche.
Cover Caliche with Soil
In some situations, adding organic soil over the caliche may be the only option available. Enough soil needs to be added to allow roots to grow. According to the University of Arizona Cooperative Extension, “Sufficient soil should be added to provide two feet total depth over the entire rooting zone,” which is 1.5 to 4 times the mature tree’s canopy. For lawns, at least 8 inches of topsoil is needed.
If you don’t plan on planting anything right away, it doesn’t have to be planting soil. You can create a layer of other forms of organic matter over the caliche, including:
- Cover crops
- Leaf mold, or
- Wood chips
These types of organic matter will need to be watered down regularly to help them break down into nutrient-rich soil.
To ensure the planting hole can properly drain, you may need to create a drainage hole before adding any plants.
After planting, make sure that water is able to reach the roots (creating some holes through caliche layers with that masonry drill bit may be necessary), and ensure that drainage is sufficient to prevent standing water/waterlogged soil.
Amend the Soil
If you’re just going to have to live with some caliche in your soil, you may want to amend it by adding sulfur. The sulfur can counteract the alkaline soil that is created by the caliche, helping micronutrients such as iron reach your plant roots.
Keep in mind that it’s best to apply sulfur up to a year before adding any plants to the soil. This gives the soil time to absorb the sulfur.
Are there any benefits to having caliche?
Caliche is used in construction all over the world. It’s used in manufacturing Portland cement, can be fired and used as a source of lime (used for stabilizing soil), and when mixed with other materials, is a strong building material. It’s also used in road construction, and in some cases can help with the process of sugar refining.
Should you still plant trees or plants if you have caliche?
Absolutely! The caliche will make adding plants or trees to your property a more difficult and labor-intensive project, but the benefits of trees make up for any difficulties.
Contact Titan Tree if you have any questions about planting trees in areas with caliche. We can tell you what needs to be done to ensure your new trees get the water, nutrients, and space they need to grow strong and healthy. And we’ll even do the work for you!