Although it seems like southwest desert soils would not be suitable for organic vegetable gardening, the reality is all they lack is water to be productive.  However, to make these soils more water efficient, and to replenish nutrients used in growing plants, organic amendments are necessary for all types of desert soils.  I will only be discussing organic methods in this section.

Sandy soils are the most challenging and ‘needy’ when it comes to amendments.  The addition of organic matter is necessary to help these soils maintain a moisture level conducive to growing healthy plants. 

Clay soils hold moisture far better than sandy soils, but if the clay is very heavy it can hold too much water and can cause root rot and other problems.  The addition of organic matter in this case is to provide better drainage and aeration of the soil, both essential to healthy plant growth.

The best types of organic amendments come from animal sources.  Although chicken manure, bat guano, fish emulsions provide nitrogen to feed plants, they do not contain other essential nutrients (such as potassium, potash, calcium and carbon to name a few) which is depleted from the soil after every growing season.  The goal is not just to feed the garden soil, but to create a soil structure which supports healthy plants and reduces the amount of water needed. You should be increasing beneficial soil microbes, attracting beneficial insects and soil building organisms such as earthworms.  The best way to tell if your garden soil is being tended to properly is the appearance of earthworms.  You can’t just add them to your garden and hope they will multiply.  The true test here is “if you build it, they will come”.

Adding animal manures such as from steer or horses also provides organic matter that helps sandy soil hold moisture and clay soil to drain better, and low levels of nitrogen to feed the plants.  Never add clay soil to sand…you will make cement, which is certainly not the goal here!!  Also important is adding straw.  Although straw does require nitrogen to break down, adding it along with the manure several months before planting will start the decomposition process and also allow the manure to ‘age’ before planting.  This is important as some manures contain high levels of salt (from feed) that needs to be leached out prior to planting to avoid burning new plants.  I purchase both steam sterilized steer manure and straw way ahead of my needs, and allow it sit for at least 6 months or longer before using. If you can find old straw that has been sitting out and halfway rotted, which is ideally what you want, you can sometimes get it for a  reduced price.

Horse manure can contain weed seeds and sometimes Bermuda grass (which you definitely don’t want in your garden), so be careful of using unless you have the time to sterilize it yourself, by placing heavy weight clear plastic over a pile and letting it cook in the hot summer sun for a few months.  This will kill off most seeds.

Manure pile-close to garden, away from the house.

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