Clean Up Warm-Season Gardens
Remove spent foliage. If it's free of disease, insects, and weed seeds, put it in the compost pile. Otherwise, it's better to discard it. Layer 4 to 6 inches of fresh organic matter, such as compost, aged manure, dried leaves, or grass clippings on top of the soil. You can let it decompose in place if you are not planting your cool-season beds yet. Or turn it all under to a depth of 12 to 18 inches. If the ground is too hard to dig, you might prefer to build raised beds.
Plant Cool-Season Annual Flowers
Transplant or sow seeds for cool-season flowers such as ageratum, asters, baby's breath, bachelor's buttons, bells of Ireland, calendula, coreopsis, dianthus, flax, geraniums, Iceland poppies, Johnny-jump-ups, lobelia, pansies, petunias, snapdragons, stock, and violets. Sow seeds for bishop's weed (Ammi majus), hollyhocks, larkspur, nasturtiums, Shirley poppies, shungiku chrysanthemums, and sweet peas.
Bulbs tend to disappear fast from the nurseries, so go early for a good selection and save them in a cool location for planting in October or November. Bulbs that perform well in the low desert include babiana, bearded and Dutch iris, crocus, crocosmia, freesia, oxalis, rain lily, spider lily, tritonia, and watsonia.
Update Your Landscape
Fall is the best time to install new landscape plants. Think about enhancements you'd like to make (creating more shade, improving energy efficiency, adding color, attracting wildlife) and then choose plants that will fit your needs. Be sure the mature size of the plant will fit its intended space, both vertically and horizontally, and avoid otherwise unnecessary pruning just to keep the plant in bounds.
Monitor Citrus Water Needs
Young trees that have been in the ground less than four years may need water every 3 to 4 days if temperatures remain high. Older trees can go every 10 to 14 days between irrigations. Water should soak 3 feet deep and be applied at the edge of the tree's canopy, where feeder roots are actively growing.