Feeding and watering established plants enables them to produce all those food and flowers that we want. Here are some specific techniques.
Feed all plants with a balanced, slow-release fertilizer containing micronutrients in addition to the basic nitrogen, phosphorous, and potash/potassium (N-P-K). Well-nourished plants not only develop into stronger plants and produce flowers and fruits and vegetables longer, they are better protected against insects and diseases and better able to withstand heat and water stress.
Water the garden deeply every week or two, depending on how consistently hot the weather has been and whether plant roots have grown deep into the soil. Tomatoes and other large plants in clay loam soil use about one inch of water in three days of hot, dry weather. Some wilting of foliage at the end of a hot, dry day is to be expected, but wilting through to the following morning indicates the immediate need for a deep watering to the roots and a gentle sprinkling of the foliage.
Refrain from overhead watering when the evenings remain warm, especially when leaves can't dry off by sunset. Fungal diseases thrive when air temperatures remain between 70 and 90 degrees, and they need only two to four hours of moist, warm conditions to develop.
Build donut-shaped water basins around trees and plants. Start the inner wall of the basin about two inches from the plant stem, or a foot away from a tree trunk. Form the outer wall of the basin just beyond the plant's or tree's dripline. Fill the area between the two walls with irrigation water. The walls hold in the water, letting it soak slowly and deeply into the root zone. Keeping the water away from the stem or trunk prevents rot from too much moisture at the base. Also, keep mulch the same distance away from the stem or trunk to allow sufficient air circulation for the roots.
Keep adding to mulches throughout the summer to conserve water, keep roots cool, and foil weeds. Remember to water well before applying the mulch, or you'll insulate dry soil rather than moist soil. Pile mulch two to six inches deep under shrubs, trees, vines, and in flower and vegetable beds. Let grass clippings dry out a bit before piling them (or just spread them thinly), or they'll clump into a mat that's impervious to later watering.
With permission from Yvonne Savio, UCCE MG LA County