As my tomato plants begin to succumb to July desert heat here in Palm Springs, I'll be taking them out, working more organic matter into the soil (mostly in the forms of compost and alfalfa meal), and planting cowpeas (Vigna unguiculata, or blackeye peas) as a summer cover crop.
The heat-tolerant cowpeas (beans, actually) will capture and deliver solar energy to the soil in the form of root exudates, which will support valuable biological activity underground. Then, when the temperatures cool off enough this fall, usually in early October, I'll cut off the tops of the plants so their roots will decompose. This all helps improve the poorer soils we have here.
I had mixed results from my tomatoes, I think mostly due to the unimproved soil plus my choice of varieties - I tried many of my old favorites just to see how they would perform in this climate. As usual, Clear Pink Early and Glacier produced an abundance of fruits (over 60 each) from short 3-foot bushes, while the hybrids Park's Whopper, Big Girl, and Pink Girl had moderate yields of 12-20 larger fruits each. Pink Girl was by far the best flavored of these.
Consistent with the experience of other desert growers, my great old heirloom varieties didn't thrive. I got a few fruits from Pineapple and Black Pineapple, but probably won't bother trying them again until I've worked on this soil for a couple years. I do hate to give up on delicious older varieties without more experimentation. Newer varieties have been bred to produce in lifeless soils with petrochemical fertilization, but the heirlooms perform best in biologically-active soils with goodly amounts of minerals and organic matter. I'll get there.
For those of you in more moderate growing zones, the timing here must seem strange. I started all my plants from seed just before Christmas and set the plants out in early February. (It can freeze here some years in January, and March 1st is regarded as the fully-safe date.)
Speaking of seed starting, some years back I read of an experiment conducted by a university researcher who tested tomato seedlings under lights set for differing timings, at half-hour intervals. The best growth came from 14.5 hours of light and 9.5 hours of darkness. I would guess that this corresponds to the springtime daylight pattern in the Andes where tomatoes were originally located??? (Please don't bother telling me that 18 hours of light works well for you - I'm sure it does, but 14.5 hours would work better!)
My planting strategy for next season will be to grow a mix of some supposedly heat-tolerant varieties (Porter Improved, Green Grape, Henderson's Winsall), along with a few smaller heirloom types (Flamme, Amerikanskiy Sladkiy, Wapsipinicon Peach) and some more hybrids (Lemon Boy, Tye Dye, Super Bush). If I had more room, there would be at least a dozen more. Given enough time, I'll have an all-star desert-adapted lineup. See many of my selections at Baker Creek Heirloom Seeds - they have a wonderful full-color work of art catalog - www.rareseeds.com or call 417-924-8917.
Also, in late August I'll start some tasty short cold-tolerant varieties (Clear Pink, Glacier, Siberian) indoors to be set out in October and (hopefully) produce over the winter months. I know I'll have to protect these plants from frosts, but by grouping them close to each other I should be able to just throw a sheet over them at night. I may start a few more of these in October to be set out in December, just to see how they do and to have succession crops.
This low-desert climate zone is interesting and has great potential, (which is hardly news to all the commercial grape, citrus and vegetable growers from Indio down to Yuma). Maybe some of the things that I learn experimenting with mycorrhizal inoculants, soil amendments, plant varieties, and timing may some day prove useful to other organic growers in severe climates.
With a growing world population and crop soils being systematically ruined by over-fertilization (corn is the biggest offender), it may be helpful to have as much information as possible about converting marginal desert soils into cropland.
And home gardeners may show the way. Who else has more ideas and tries so many different methods?
Good growing, my friends.