In the Garden:
Southwestern Deserts
February, 2010
Regional Report

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Organically rich soil produces healthy vegetables, flowers and herbs.

Building Healthy Garden Soil

In my previous report, I covered the basic characteristics of desert soil, explaining that native soil is great for growing native and desert-adapted landscape plants, with no amendments needed. However, if you wish to grow annual vegetables, flowers and culinary herbs, it's essential to amend your garden beds.

Many of our favorite annuals are native to regions with soil containing lots of organic matter. By definition, an annual plant germinates, develops roots and foliage, blooms, sets fruit, goes to seed, and ultimately dies, in one brief growing season. To help sustain such frenzied activity, provide your annuals with organically rich soil that retains moisture. Here's how to amend what you've got.

Choose a location for your garden that receives 6 to 8 hours of full sun daily. Morning sun and afternoon shade (for warm-season gardening) is ideal. Good drainage is key and desert soil may drain poorly for various reasons. Your soil may contain lots of clay, which retains water but turns into adobe brick when dry. It may have been compacted by heavy equipment. Some locations contend with a rock-hard layer of caliche (calcium carbonate) below the surface that impedes water flow. Lots of people blame their difficult-to-dig soil on caliche, but it's not as common as we like to think. Compacted, hard rocky soil may be just compacted, hard rocky soil- especially if heavy construction equipment graded the area before building.

Traditional Garden Building
Start by loosening soil to a depth of 12 to 18 inches to allow annual plant roots and moisture to penetrate easily. Depending on your soil conditions (and back strength), you might be able to do this with a shovel or spade, but I wore out a pickax swinging it at my hard ground years ago. If your ground is undiggable, water it 2 or 3 days in advance, let it dry somewhat, then dig the top layer of softened soil. Never attempt to work wet soil, which destroys its structure for all time. Continue to "water and dig" a few inches at a time over a period of days (or weeks). A soil fork is another helpful tool. Inserting the fork's tines will loosen and open up cracks to help water and root penetration.

Once soil is loosened to 12 to 18 inches, spread 4 to 6 inches of compost or well-aged manure on top of the bed. This may seem like a lot, especially in comparison to other regions of the country, but desert soils contain almost no organic matter. Gypsum or garden sulfur or can be added according to package instructions to improve drainage in clay soils. (Sulfur also slightly reduces pH on a temporary basis although it won't greatly influence our high-alkaline soils.) Turn it all under and rake smooth.

Tasks are never complete when it comes to soil building. Before each planting season, add another 4 to 6 inches of organic matter. If you garden where there are both cool and warm planting seasons, this means twice annually. Over time, your soil will transform into dark, nutrient-rich soil that is easy to work.

Ugh! This is too much work you complain. I tend to agree. I'm not nearly as enthusiastic a digger as I used to be! In my next report, I'll cover a less labor-intensive method of soil building.


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