Containers. You can purchase a flower-filled pot at a nursery, but it's much more fun to make your own ― especially if you begin with a theme and a 22- to 24-inch-wide container. For a red-and-purple hummingbird pot, try purple Mexican bush sage, 'Firebird' penstemon, scarlet Phygelius capensis, and dark purple Salvia guaranitica. To attract butterflies, plant purple aster, gold Coreopsis verticillata 'Zagreb', yellow lantana, and Mexican bush sage.
Fall vegetables. Sunset climate zones 1, 2: Below 5,000 feet, plant bush beans, beets, broccoli, cabbage, carrots, cauliflower, green onions, peas, spinach, and turnips for fall harvest. You can also plant winter squash between some of the spinach; the spinach will be ready to harvest before the squash takes over.
Perennials. To start new plants for fall, take 5-inch-long cuttings (without flowers) of dianthus, geraniums, salvias, Shasta daisies, verbenas, and other herbaceous perennials; dip them in rooting hormone; and plant them in a 2- or 4-inch container filled with a mixture of one part perlite and one part peat moss. Water, then enclose containers in plastic bags to keep the humidity high; set outside in bright, indirect light. Open the bags to allow air circulation every few days. Check for rooting in about two weeks. Once rooted, allow plants to grow for several more weeks before transplanting.
Adjust automatic controllers. Depending on where you live, the weather this month can be hot and sunny or cool and foggy. If you water with an automatic controller, make sure it runs the irrigation system often enough so plants get the water they need, but not so often that the soil stays overly wet. As a test, check soil moisture just before the system is due to come on by using a soil probe or digging down 3 to 6 inches (depending on size of plant) with a trowel. If the soil seems too dry or too moist, adjust the controller.
Coax bougainvillea blooms. Zones 7-9, 14-17: Bougainvillea blooms best when it's kept on the dry side. Allow the top several inches of soil to dry out between waterings.
Cut back cane berries. After harvesting June-bearing blackberries, boysenberries, and raspberries, cut spent canes back to the ground and tie up new ones as they develop.
Deep water trees. By midsummer, the soil has long since dried out from last spring's rains. If you haven't watered your mature trees (established three to five years), they may be suffering from drought stress. Deep water citrus, fruit, and flowering trees once every week or two (every week in hot, inland climates). Water less-thirsty trees ( Arbutus 'Marina', carob, Chinese pistache) about once a month or so. Water newly planted trees regularly (don't let the soil dry out); gradually reduce frequency after a year or so.
Trim and feed dahlias. When the first bloom flush starts to fade, trim back dahlias and fertilize them to encourage new growth.