Mild-winter climates: Feed and water roses deeply to encourage a round of fall bloom.
Cold-winter climates: As you cut flowers to take indoors, shape plants. Allow a few hips to form, completing the flowering cycle and ushering plants into dormancy.
Get first pick of bulbs
Gather your flower bulbs as soon as they become available in nurseries. If you're first in line, bulbs aren't likely to be mixed together yet, and you'll have the best selection of the year.
Plant batches of them shoulder-to-shoulder in a pot for three weeks of portable spring color.
Mild-winter climates: Refrigerate the bulbs in paper bags (away from ripening fruit) six weeks before planting.
Harvest fruits and veggies
Keep them picked to keep rot from taking hold.
Eggplants. Harvest fruits when they're immature and shiny.
Peppers. You can pick any pepper when the pod is firm and fully developed. But for best flavor, pick after the pods show color.
Tomatoes. Pick after fruit colors fully. In fall, when night temperatures drop below 55°, pick any tomatoes with some color and ripen them indoors on a windowsill (dark green fruit never ripens).
Multiply by dividing
Dig and divide perennials such as bee balm, daylily, and Shasta daisy to reinvigorate plants and increase size and numbers of blooms.
Pop the whole clump out of the ground with a shovel or spading fork. Hose off the rootball, removing as much soil as possible.
Use a butcher's knife or pruning saw to cut the clump into quarters. Pull the quarters apart and further divide them with your hands or a knife. Each division should have a sturdy root and one to three leaf fans (more fans result in faster growth and flowering).
Plant a few wildflowers
Sow in weeded, prepared beds, being careful to plant a line of seed around the edge of the bed so it won't look ragged-edged (unless it's in a wild part of the garden).
Sow some of the same seed in a flat so you'll have a reference plot that shows the difference between weed and flower seedlings when both emerge in spring.
Move to cool-season annuals
Mild-winter areas: Try seedlings of pansy (pictured), calendula, dianthus, English daisy, Iceland poppy, lobelia, nemesia, ornamental cabbage and kale, primrose, schizanthus, snapdragon, stock, and viola. Continue to deadhead existing plants, and fertilize one last time early in the month.
Cold-winter areas: Pull up existing plants when frost hits. Shake soil off the roots and toss them onto the compost pile.
Plant ornamental grasses
Ornamental grasses bring texture, motion, light, and even sound to garden beds and borders. They also make great companions to potted annuals, perennials, herbs, succulents, and broad-leafed plants.
Weekly irrigation is sufficient for most varieties, and many get by with even less water. Don't bother with fertilizing ― grasses look better without it. Leave your chemicals in the garage; pests and diseases rarely affect them.
Choose trees for fall color
This is the best month for planting shrubs and trees that have great fall color; shop now and you'll see just what you're getting.
Cold-winter climates: Protect young tree trunks. Bright winter sunlight can make young tree trunks split and crack down their south sides. Protect them with a coat of white latex paint or a length of corrugated drain pipe split lengthwise. After trees are three or four years old, thickening bark prevents sunburn.
Get rid of pests
Mild winter climates: Control insects and snails. As fall flowers and vegetables start putting on tender new growth, aphids, white flies, and snails often move in to feast. The secret is to control them before populations get out of hand. Hose off plants invaded by aphids and white flies, then spray for the insects that remain with a pesticide like insecticidal soap. Bait for snails with iron phosphate (it's nontoxic to pets and humans), and squash them whenever you see them.
Cold-winter climates: Prevent snow mold. Rake the thatch that harbors snow mold out of the lawn, then spray turf with a fungicide, such as benomyl.
As you clean out the summer garden, pile everything but diseased material onto the compost pile. Turn the pile and keep it moist. By next spring compost should be ready to use.
If you have compost already, work it into your soil now for earlier spring planting. Leave the surface rough so it absorbs winter moisture; the freezing-thawing cycle will break apart clods.
Cold-winter areas: Use the compost as a mulch to protect bulbs, perennial flowers and vegetables, permanent plants, and strawberry beds.