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Around here, a lot of people who try plant something in their yard or landscape are not too surprised if, or when, it dies. Anybody who thinks that desert gardening consists of - digging a small hole in the soil and filling it up with a plant straight out of the pot or the box, well, that person is going to have a whole series of dead plants. And we know there's a ton of reasons why that can happen, and does happen.
But why, really? There are places all over the world where pretty much all you have to do is - Plant a seed, get a plant. Plant a small tree, give it a little care, and you'll get a big tree. Maybe in other places, but not in Southern Nevada.
Why is that? The first thing that comes to mind might be the most obvious - our weather: incredibly hot (except for when it's cold) and incredibly dry. Remember - the Mojave is the dryest desert in North America.
No doubt, our climate's a big problem, especially for non-adapted plants. However, you can do certain things to modify the environment, like giving it shade, mulch and water, but they're not going to make much difference in plant survival if you don't take a close look at the soil.
If you ask a person who doesn't live around here about soils in the desert, they'll probably say 'sand'. Picturing the Sahara. And there are some sandy soils here.
If you ask a person who does live around here about the soil, they'll probably say 'caliche' unless, of course, they laugh and say 'what soil?' Not funny. We do have soil. It's just different from most places.
In many parts of the valley, it's hard to make a hole in the ground. There is caliche, which is a kind of conglomeration of limestone, rock and other junk, which keeps the soil quite alkaline. It's also mighty hard to work with. Always a challenge to dig in it, or in soil that has a lot of it. But caliche isn't in all the soils around here. In fact, sometimes when people are complaining that they can't dig in their soil, the problem isn't caliche, but just compacted soil. The weight of earth moving machines and construction equipment just mushes the soil all together into a hard pan. Almost as tough as rock. As if we didn't have enough problems.
We certainly do have soil. Maybe I should be clearer. Not soil, but 'soils'. Plural. In a lot of places, you can make generalizations about the soil, but not here. Different parts of the valley have very different soil types and textures. I've been told that there're over 20 soil types in Las Vegas alone.
There are three fundamental components to soil - clay, which is composed of flat microscopic crystals; silt, which is slightly larger, and sand, which is enormous compared to the other two. Soils with no sand tend to have terrible drainage, and soils with mostly sand will dry up in an instant because water whips right through them. It's the relative amounts of each of those components that determines what kind of soil you have.
But when the soils are so different from one part of our area to another, what kinds of generalizations can be useful? If any?
Here's a Generalization:
Our soils are often either mostly white-ish or reddish. The colors are mainly due to the clay and what's in it. We all know clay; as kids we played with modeling clay, and some folks (not me) even occasionally ate some. The white indicates that it has a lot of free minerals, like calcium deposits and salt (yes, like table salt). The reddish soils are high in iron (don't they kind of look like they're the color of rust?)
Here's another generalization:
Ours soils have very little organic matter. This means that there is little native fertility available. Unless you're growing plants from the Mojave or another desert, you need to improve the soil by adding some kind of soil amendment like compost. The garden will benefit from it.
If you know you have mostly sand, then you want to add something to slow down drainage, like compost or clay. If you have no drainage, then you need to do other remediation.
You can get a rough estimate of the proportion of the components in your soil by a little test using a jar, some soil, and some water. There's also a little exercise you can do with kids, playing with mud to determine how much of each you have. We have the procedures for each of these written up at the Cooperative Extension office, if you'd like to try them. I think they're fun. Great excuse to put your hands in the dirt.
For KNPR's Desert Bloom, this is Dr. Angela O'Callaghan of the University of Nevada Cooperative Extension.