Divide plants in perennial beds before cool weather arrives

  • Continue to harvest veggies this season as they ripen.

    Continue to harvest veggies this season as they ripen. Courtesy of Chicago Botanic Garden

By Tim Johnson
Chicago Botanic Garden
Posted9/19/2021 7:00 AM

Divide perennials that bloomed in spring and summer as needed. Best to do this in September so plants have time to establish before winter sets in. Mulch the newly planted divisions.

• Fertilize your lawn in early September to improve the color and vigor of the grass. Nitrogen is the nutrient required the most, although too much nitrogen can cause excessive top growth and disease problems. In most cases, a rate of 1 pound of nitrogen per 1,000 square feet of lawn is adequate.


Many soils in Chicago area have adequate levels of phosphorus so it is likely not needed for your lawn. Some villages ban the use of phosphorus to preserve water quality, as it can fuel algae growth in lakes and streams. If you only fertilize your lawn once a year, this is the best time to fertilize.

• Autumn is a good time to core aerate to reduce soil compaction and thatch, if you did not aerate in spring. Core aerating once a year is enough for most residential lawns with normal use. Very high use lawns will benefit from being aerated twice a year.

Core aerating is best done when the ground is somewhat moist. Leave the soil/grass plugs on the lawn to break up and filter back down to the soil level. The plugs typically break down in seven to 14 days. Mark sprinkler heads and light fixtures in the lawn so they will not be damaged.

Autumn also provides an opportunity for overseeing to help improve and thicken up your lawn. Keep the seed moist for good germination.

• 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.

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Continue to snip herbs to use fresh, to dry or to freeze. Try making some extra pesto and freezing it an ice cube tray. Pop out the cubes when frozen and store 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 a light 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 only compost healthy plant material.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.

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