Even if the heat comes blasting into your corner of Southern California, there's plenty to do. The biggest task at hand is preparing for planting season: Map out your new trees and shrubs, bulbs (which begin arriving in stores in September), winter vegetables, perhaps some ground cover.
Some other ideas for August:
Hot weather germinates seeds quickly, so August is a surprisingly good time to start seeds in pots or packs -- or even sow a few things in the ground. Start them in small flats or pots, placed in partial shade.
Try cool-season flowers such as calendula or fall vegetables such as broccoli, Brussel sprouts, cabbage and cauliflower. Cole crops do best if transplanted as seedlings because they can go a bit deeper in the ground, providing support for crooked or weak stems. Don't plant seeds too deep, and keep snails and slugs at bay by keeping your containers off the ground.
If you're determined to sow seeds in the vegetable garden, one trick is to dig a trench about 2 inches deep, then lightly cover the seeds with soil and allow the trench to provide some shade.
Some gardeners have found that 'Champion,' 'Celebrity' and 'Sweet 100' tomatoes will produce in winter if planted now. The vines will not produce many tomatoes, and what fruit you do get may have thick skin, but you will have a fresh crop to go with that winter lettuce.
Pick a spot against a south-facing wall for additional heat. Ignore conventional advice and don't plant deep; the vines will do better in winter if you keep roots closer to the surface. Be prepared to cover them with a sheet at night if the weather turns frosty.
Sow sweet pea seeds by Labor Day, and you can have bouquets of fragrant flowers by Christmas. Choose early-flowering varieties such as 'Early Multiflora' and 'Winter Elegance.' These early bloomers usually have shorter stems.
Prepare the soil well with lots of compost and fertilizer, and soak seeds overnight before sowing. Plant them 1 to 2 inches deep, pressing down so the soil is touching the seeds. Water two or three times each week till you see sprouts; don't let the soil get soggy or the seeds will rot. Protect against snails, slugs and birds (try netting).
Naked ladies (Amaryllis belladonna) are South African bulbs that bloom at the end of summer and get their common name from the fact that they have no leaves while in flower. The foliage follows in winter. They are tough plants that get by with rainfall alone, no irrigation. The denser the clump, the happier they seem to be, but if you need to thin them, wait till after they flower. Bury them so that the neck and the top third of each bulb is aboveground.
Bearded irises rhizomes do need to be divided every few years or they will stop blooming. Divide them now and the flowers will grow enough by spring to bloom. Dig up the rhizomes and discard any that are shriveled, leaving only the fat, healthy ones. Shake or rinse soil from the roots. Cut back leaves to about 6 inches and trim wiry roots by about one-third. Bury most of the rhizomes, but don't cover the tops; about half an inch should be exposed to sun. They should be spaced about a foot apart, facing whatever direction you want them to grow.
Even California natives and water-sipping Mediterranean trees and shrubs benefit from a deep soaking in August. On the hottest days, potted plants may need watering twice a day -- something to keep in mind as you make future selections.
If you haven't fixed broken sprinklers, do so now to stop that stream of wasted water flowing into the gutter. Once you're certain the sprinklers are functioning efficiently, set them to come on around 4 a.m., when breezes are less likely to blow water from your intended target. More irrigation will go to the roots, and less will be lost to evaporation.