There are some precautions for plants in hot weather. The most important thing is to make sure your irrigation is dialed in. Consistency is more important than volume; daily water is a must when it’s this hot and dry. We Californians don’t have to feel guilty about watering each day because we had plenty of rain and snow this past winter, but in the coming years, that might not be the case. So let’s talk about preserving moisture NOW, so you’re all set when that moment comes.
The amount of organic matter (OM) in your soil is probably the most important thing, acting as a sponge, holding on to moisture. Clay soil already has good water retention and OM can help further. Sandy soil is terrible at holding on to water, so OM will be extremely important in that situation. How to include more OM? Add compost around your plants and on top of your beds each year, mulch the heck out of everything using whatever you can find, and keep a living root in the soil at all times.
Plants pump sugars and carbohydrates (carbon) down into the soil to feed the microorganisms that live there; in turn those organisms provide nutrients to the plant. Plants do not grow well alone - they all do much better with a lot of roots in the ground around them, with a lot of diversity of species. Think of a meadow, crowded with forbs and grasses, or a forest, covered with trees and ferns. Bare space gets colonized. If you don’t want your garden colonized with weeds, be prepared to colonize it yourself.
You can kill two birds with one stone by mulching with living plants. If your cover is complete enough, it will do the job of mulch; that is, shade the soil, suppress weeds, and keep things moist under the canopy. To that end, I’ve begun seeding any possible bare space, even in my veg beds, with a cover crop of some kind. Some of the tomatoes, the ones that didn’t have basil or cilantro growing under them, just got a seven-species cover crop sown beneath them (a warm season mix from Walnut Creek Seeds). I’ve seeded buckwheat in my melons, cosmos in my winter squash, and sunflowers in my pumpkins. You may feel that this would take nutrients and water away from the main crops, but the opposite has been proven true; when there is lots of diversity under the soil (in the rhizosphere, or root zone), MORE nutrients are available.
Of course, this kind of microbial diversity takes time. I find that things get better all the time, as long as I keep as much diversity of planting as possible. Also, with this system, you don’t have to worry quite as much about crop rotation. And, there are lots of other benefits to this besides water retention and greater nutrient availability, like the attraction of predatory insects that will take care of the pests in our gardens.
I encourage you to check out the latest issue of California Agriculture from UC Davis, which has a summation of a recent study about how cover cropping/multi-species cropping can really improve soil (in conjunction with no-till practices, which of course you’re already doing, right?). The bottom line is that there is more fungal hyphae in soils that are cover cropped (and not tilled). That means there are more connections between the plant roots, working in symbiosis. Here’s a little quote, sorry for starting in the middle of a sentence:
“… allowing roots greater access to water and nutrients (in exchange for carbon). Fungi, however, are more sensitive than other microorganisms to physical disturbance. Adopting no-till as a conservation man- agement practice eliminates or greatly reduces both disruption of fungal hyphal networks and redistribution of organisms and nutrients in the soil profile. Use of cover crops, meanwhile, provides more abundant and varied sources of organic carbon.”
So this system in the soil allows for greater uptake of water and nutrients. That should be enough to get you to think about adding many plant roots to one space!