Continue to harvest vegetables as they ripen.
Warm-season crops like peppers and tomatoes should be picked as soon as possible. Full-sized pumpkins need to remain on the vine as long as possible to achieve their maximum size.
Continue to snip herbs to use fresh, to dry or to freeze. Try making some extra pesto and freezing it in an ice cube tray. Pop out the cubes when frozen and store them in a plastic bag for use this winter.
Collards, kale and brussels sprouts will have improved taste if they are allowed to be hit with frost before harvesting.
Maintain good sanitation throughout the vegetable garden. Remove diseased plants immediately, as well as those that have finished their growth cycle for the year. It is best to compost only healthy plant material since most home compost piles will not get hot enough to kill disease organisms.
• Powdery mildew (a disease that causes a grayish, powdery film on leaves) is present now in many gardens. Common plants that can get powdery mildew are lilacs, phlox, bee balm, zinnias and nannyberry viburnum.
This disease typically occurs in the late summer when the weather is warm and humid. Fungicides can help control powdery mildew, if they are applied before the infection becomes severe.
In most cases, there is no need to apply any controls for powdery mildew at this time of year, nor is it generally ever worth spraying for. Other options include selecting more mildew-resistant varieties, or moving the infected plants to an area of the garden that has better air circulation.
• Divide perennials that bloomed in spring and summer as needed. It's best to do this work early in the month so the plants have time to establish before winter sets in.
A sharp, flat spade works well for dividing perennials. It is important to mulch the newly planted divisions and provide supplemental water for the rest of the gardening season as you would with any other plant you may have purchased and installed.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.