Cool-season flowers. Set out seedlings of flowering cabbage and kale, pansies, and violas.
Cool-season veggies. Sunset climate zones 4-7, 17: As soon as possible, sow seeds of arugula, leaf lettuce, mustard greens, and radishes for fall harvest. Set out nursery-grown seedlings of these, plus cabbage, kale, purple-sprouting broccoli, and spinach. More: Guide to salad gardens
Cover crops. As you remove annual veggies, sow seeds of cover crops like Austrian field peas, crimson clover, and vetch. During the winter, these plants will reduce soil erosion from wind and rain. Next spring, you simply till them under to improve the soil's organic content and texture. A good source for cover crops is Territorial Seed Company (800/626-0866).
Landscape plants. Autumn is the best time to set out trees, shrubs, vines, groundcovers, and perennials. Buy them in containers at the nursery (or ask neighbors for divisions of perennials). Plant right away and water thoroughly. Rainfall and cool temperatures will encourage plants to develop strong roots over winter so they'll be well established for the next growing season.
Lawns. Zones 1-3: Start lawns from seed anytime through mid-September; lay sod through mid-October. Zones 4-7, 17: Sow grass seed or lay sod anytime this month. Consider replacing thin or worn patches of turf with drought-tolerant groundcovers or gravel pathways. More: Fall lawn care
Spring-blooming bulbs. Shop catalogs and nurseries for bulbs; get them into the ground soon. For long-term performance, choose among bluebells, camass, crocus, daffodils, fritillary, grape hyacinths, snowdrops, species tulips, and star of Bethlehem. Hyacinths and standard tulips remain viable for two or three years. Step-by-step: Planting bulbs in pots
Rose care. After the fall flush of bloom, don't deadhead faded blossoms; leave them to form fruits, called hips. This helps roses transition to winter.
Control fungus gnats. These small, dark-winged insects flit around houseplants and breed in the potting soil. To stop them, cover the soil with a layer of sand (if you have cats, use gravel).
Divide perennials. Now's the time to dig up, divide, and replant spring- and summer-flowering perennials, including oriental poppies, peonies, Shasta daisies, and Siberian irises. Divide fall bloomers after flowering or wait until new growth starts in spring.
Make compost. As you remove spent flowers and vegetables, toss them on the compost pile. But don't add diseased plants or weeds that have gone to seed. Step-by-step: Make your own compost bin