In the Garden:
Southwestern Deserts
August, 2014
Regional Report

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Cool weather-loving cabbage is a good fall crop in the low desert parts of our region.

Getting Desert Soil Ready for Veggies

It may be difficult to fathom in the midst of summer temperatures, but cool-season vegetable planting is not too far off. In the low desert it's best to wait until temperatures drop towards the end of September or early October, which is less stressful on the plants, before planting outdoors.

But another way to get a jumpstart on the season is to sow seeds indoors in from late August though September. They'll be ready for transplanting outdoors in six weeks or so. Veggies in the cole crop family (bok choy, broccoli, Brussel sprouts, cabbage, Chinese cabbage, cauliflower, and kale) are good cool-season choices for transplants. Salad greens are another possibility, but root crops, such as beets, carrots, onions, parsnips, and radishes, are best sown directly in the garden as they don't transplant well.

Desert Soil Characteristics
To have a good home for all those seedlings to go to, start planning now to improve your soil before fall planting time arrives. Rich black soil that you may be used to from gardening in other regions of the country develops, in part, because their native plants drop large amounts of litter. This organic matter decomposes with the aid of plentiful rainfall, eventually turning into a layer of dark, crumbly humus. Desert soil doesn't contain much organic matter because desert plants drop insignificant litter. Visualize the leaf size of a palo verde tree versus a maple tree or the build-up of plant material at the base of a saguaro versus a pine tree. There just isn't enough organic matter to accumulate and turn into black earth. In fact, desert soil contains less than 1/2 of 1 percent organic matter.

Annual vegetables complete their life cycle in one short growing season. Organically rich, well-drained soil is essential to fuel this growth burst. Thus, if you want to grow nonnative veggies, it's essential to add compost or other organic matter to garden beds. (Another option is to seek native vegetable varieties, such as tepary beans, that are adapted to desert soil conditions.)

Building Rich Garden Soil
Layer 4 to 6 inches of compost, mulch, or well-aged manure on top of the bed. If you need to improve drainage in clay soils, spread soil sulfur or gypsum according to package instructions. (Sulfur also slightly reduces pH on a temporary basis, but it won't permanently alter desert soil's high pH.) It's also a good idea to incorporate a fertilizer containing nitrogen and phosphorous, following package directions for amounts. (Desert soils typically contain sufficient potassium, but check with your county cooperative extension office for local recommendations.) Turn it all under to a depth of 12 to 18 inches and rake smooth. Perform this task before each planting season and over time you will develop dark, crumbly, nutrient-rich soil that is a pleasure to sink your trowel into.

You can plant immediately if you choose, or water the soil to germinate weed seeds and remove them before planting. Of course, this won't chase away all weeds, but it can cut down on initial competition with young veggie seedlings.


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