Autumn is the best time to tackle a bushelful of chores, such as attacking broadleaf weeds and fertilizing the lawn. Follow these tips to save time, keep plants healthy this winter, and prepare your garden for a running start come spring.
Fertilize the lawn
Autumn is an ideal time to fertilize grass. It's not meant to stimulate growth, though--instead this fertilizer will feed grass roots for an early green-up next spring. Apply fertilizer according to package directions. (Different grasses and soil types require different amounts of fertilizer.) Many experts recommend an N-P-K ratio of 3:1:2 or 4:1:2, so look for fertilizers with an analysis of 30-10-20 or 8-2-4, for example.
Perennial weeds such as dandelions and creeping Charlie are more susceptible to treatment in the autumn, so seize the chance to knock them out. Hand-pulling, though difficult, is often effective, as is carefully dousing a weed with boiling water. Among chemical choices, systemic products work best because the plant absorbs the product and takes it down to the roots. (Always follow label directions exactly.) Annual weeds pose little threat come autumn unless they flower. If you prevent these weeds from going to seed, you'll see fewer show up next year.
Seed the lawn
If your lawn has damaged areas, patch them with grass seed in early autumn. It's best to wait until daytime temperatures stay consistently below 70 degrees F before planting fall grass seed. Water until established, and the young grass plants will have a head start come spring. (It's a good idea to use a lawn aerator before seeding to give your seeds an even better chance. Aerators remove small plugs of soil to encourage water and fertilizer penetration.) Gardeners in warm winter areas can overseed lawns with annual ryegrass now. Rye will remain green during the winter when warm-season grasses, such as Bermuda, go dormant. As warm-season grasses green up in spring, the annual ryegrass will wane.
Trees and perennials that keep their foliage over winter need proper watering before hard frost. This includes azaleas, rhododendrons, yews, pines, spruces, and most other needle-leafed trees. If rain doesn't naturally supply enough water, give these plants a good dousing now--an inch a week if you can--to help the roots and leaves store enough moisture before frost. Otherwise, winter conditions can dry out the foliage and cause damage.
In all but the coldest areas, autumn is a good time to transplant or divide perennials because air and soil temperatures have cooled and plants will grow more slowly and have less transplant stress. Allow several weeks between the time of transplanting and the first expected freeze so the plants can become established before winter. Early- to mid-autumn is a perfect time for planting new perennials, trees, and shrubs.
Cut back, or not
After perennials begin to turn yellow in autumn, many gardeners cut them back to discourage pests and diseases that can overwinter in the foliage. On the other hand, some gardeners like to leave their plants standing until spring. Leaving the foliage on perennials offers visual interest--and in colder areas it helps plants catch snow (a great winter mulch). Seed heads offer winter bird food, too. Plants that are particularly good for winter interest include various ornamental grasses, astilbes, and liatris.
If the soil freezes in your area, protect your perennials with mulch. Winter mulch protects the soil from freezing and thawing (called heaving). Heaving can push plant roots and crowns up out of the soil, where they are exposed to cold air and drying winds. Because mulch keeps soil temperatures even, apply it only after your soil has frozen (when daily temperatures no longer rise above freezing).
Start perennials from seed
For best germination, start fresh seeds of perennials such as peonies, foxtail lilies, irises, and daylilies in autumn. To do this, plant the seeds in a moist, sterile seed-starting mix in a cold frame. Keep the mix moist, but not wet. For specifics on starting plants that do well in your area, check with your county extension office.
Don't fertilize the garden
Unlike lawns, garden plants don't need fertilizer in fall. Perennial plants (including trees and shrubs) need to slow down their growth before the onset of winter. Don't fertilize after midsummer unless you use a slow-release, long-term organic fertilizer.
Bring plants inside
Tender plants such as passionflowers and lemon verbena need to come inside before the first frost. To help tender plants adjust to indoor light levels, move them to a shady spot outdoors for a couple of weeks. Before bringing them inside, check them for pests and give them a good shower with the hose. Indoors or out, this is a good time to cut them back slightly--up to one-fourth of the plant.
In areas with freezing winters, porous containers such as terra cotta need to be tucked under cover for the winter. Otherwise, water can become trapped in the pores, freeze, and expand enough to crack the container. Sterilize containers with a solution of 9 parts water to 1 part bleach so they do not carry over any diseases for next season.
Prep the beds
Tilling vegetable and flower beds in autumn gives you the chance to start planting that much earlier in spring. It is especially useful in areas with late, wet springs. Mulch your new beds over the winter and avoid compacting the soil.
Lift any tender bulbs, such as callas, cannas, glads, and dahlias, that you want to save for next year. Wait until the first frost kills the foliage--that signals the bulbs to go dormant on their own. Carefully dig the bulbs and wash them thoroughly with water (to avoid any disease problems over the winter) and let the bulbs dry in the sun for a day or two. Then store them in dry sand, peat moss, or sawdust in a cool garage or basement (ideally, 40 to 50 degrees F and 50 percent humidity). You can leave caladiums and other tender bulbs grown in containers in their pots. Stop watering once the foliage starts to yellow, store them inside, and do not water again until spring.
For most of the country, autumn is the time to plant spring-flowering bulbs, such as tulips, daffodils, and crocus. As a general rule, plant bulbs three to four times deeper than their height. In lighter, sandy soils, they can be planted a bit deeper; in heavier soils, plant slightly shallower.