September Gardening Tips

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Annuals and Perennials

  • Mid to late September is a great time to add accent plants, like vivid mums and starry asters, that will provide autumn colors in the landscape. Use them along with cool-colored ornamental cabbages and kales to replace bedraggled annuals in containers as well.
  • Watch for frost warnings and cover tender plants.
  • Remove and compost spent annuals and fallen leaves.
  • Weed and mulch perennial beds using a loose organic material such as bark chips or leaves to keep down weeds, preserve moisture, and give roots a longer time to grow before the soil freezes.
  • Outwit hungry squirrels and chipmunks by planting hardy bulbs in established groundcovers.
  • Lift and store tender bulbs, such as cannas, dahlias and gladiolus, after first frost.
  • Perennials like daylilies and bearded irises can still be dug up and divided.
  • Visit a local nursery or garden center and select spring flowering bulbs to add to your gardens. Plant the bulbs among perennials, under trees and shrubs, or in larger groups for a splendid spring show. Choose colors that complement other spring flowering plants as well as nearby plantings. Work a little Bulb Booster or 5-10-10 into the bottom of the planting holes.
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Education and Events


  • Take cuttings of begonias, geraniums, coleus, impatiens, and fuchsias to grow as houseplants. Cuttings can be made one-quarter inch below a node, which is where the leaf meets the stem, dipped in rooting hormone and inserted into a potting medium in a bright location but not in direct sunlight and kept moist.
  • Smaller tender perennials, like some fuchsias, can just be cut back and overwintered in cellar windows as long as not allowed to completely dry out. If frost threatens, bring houseplants indoors.
  • Pot up or propagate herbs to bring indoors for winter use.
  • Examine houseplants carefully for insect pests before bringing them back inside. Give them a good grooming if necessary. You may want to spray plants with insecticidal soap after hosing off the foliage. Let the plants dry first.
  • The third week in September is National Indoor Plant Week. Take some time to get your houseplants in tip top condition. Give all your plants a good grooming and check for any pests.
  • Move the houseplants to their indoor locations before the furnace gets turned on so they can start becoming used to the lower indoor light and humidity levels.
  • Potbound plants will appreciate larger living quarters. Repot crowded plants now while this task can be done enjoyably outdoors.
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In the Vegetable Garden

  • Late season cabbage and beets can stay in the garden until a light frost for best flavor. Some root crops, including certain varieties of beets, carrots and parsnips, may be left in the ground for storage. Wait until temperatures drop and growth stops and cover with a thick layer of straw or leaves. Harvest as needed during the winter. This may not be an option in areas with heavy vole populations.
  • Harvest onions once tops have fallen over and necks have started to dry down and shrink just above the bulb.
  • Direct plant shallots and garlic for next year in the garden.
  • Get a jump on next year’s lawn and gardens by having a soil test done through the UConn Soil Nutrient Analysis Laboratory
  • Wood ashes have a pH of 11.0 and contain phosphorus, potassium, and calcium. They can be used as a limestone substitute in vegetable and flower beds if the soil pH needs to be raised and these nutrients are recommended.
  • Watch for frost warnings and cover tender plants to extend the season.
  • As tomatoes end their production, cut down plants, pick up any debris and put dead/diseased plant parts in the trash or take to a landfill. Many diseases will over-winter on old infected leaves and stems so these are best removed from the property.
  • A cover crop of annual ryegrass can be sown in the areas of the vegetable garden that would benefits from additions of organic matter.
  • Cover beds with untreated lawn clippings and leaves picked up during fall mowing.
  • Compost can also be dug into garden beds. Note that composts vary in their nutrient content. If nutrient levels in your gardens are already high, incorporate lower nutrient leaf-based composts to increase organic matter.
  • Be prepared to cover remaining vegetables with landscape fabric or cloth if an untimely frost occurs.
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  • As the days grow cooler, insects like the boxelder bug and the Asian lady beetle will invade homes seeking overwintering sites. Neither insect will harm you or your home but they can be a nuisance. Seal and caulk cracks and apply weather stripping around doors to keep them out.
  • Pick and discard any dropped apples that show signs of apple maggot.
  • Remove bagworm egg masses from evergreen shrubs to eliminate the spring hatch from over-wintered eggs. 
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Landscape and Lawns


  • Rake up leaves, twigs, and fruit from crabapple trees and throw them in the garbage to help control apple scab disease.
  • Pick and discard any dropped apples that show signs of apple maggot.
  • Do not fertilize fruit trees in late summer. Doing so may cause new growth that will not harden off before winter.
  • Continue to water any new shrub or tree plantings until the first hard frost if fall rains are scarce.


  • Re-seed bare patches on your lawn and prepare the ground for sowing a new lawn while the soil is still warm.
  • Apply fall fertilizer to lawns between Sept. 15th and Oct. 15th.
  • Now is the time to de-thatch and aerate lawns to promote root growth if necessary.
  • Use a mulching blade to finely chop fallen leaves and let them decompose on the lawn.
  • Avoid the spring rush and have your soil tested now by the UConn Soil Nutrient Analysis Laboratory. Incorporate the recommended amounts of limestone and fertilizers into the lawn for next year’s growing season.

Trees and Shrubs

  • Early fall is a good time to plant trees and shrubs and allows time for the root systems to get established before the ground freezes.
  • Continue weeding garden and shrub beds.
  • Remove and compost fallen leaves.
  • Plant peonies now, but make sure the crowns are buried only one and a half to two inches below ground level. Planting them deeper than two inches may keep them from blooming next spring.
  • If pesky seedlings of woody plants, such as maple, elm or hackberry are found growing in your yard, remove them as soon as possible so they won’t take over gardens and other landscape plantings.
  • Continue to water any new shrub or tree plantings until the first hard frost.
  • Remove bagworm egg masses from evergreen shrubs to eliminate the spring hatch from over-wintered eggs.

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  • Outwit hungry squirrels and chipmunks by planting bulbs in established groundcovers. Lift and store tender bulbs, such as cannas, dahlias and gladiolus, after the first frost.
  • Limit herbaceous plant material located a few feet away from the house to eliminate hiding places for insects and mice that could wind up indoors as temperatures plummet.
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Yard Accessories and Miscellanea

Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed.

For pesticide information please call UConn Home and Garden Education Center weekdays, in Connecticut call toll free 877-486-6271. Out of state call 860-486-6271

Revised by the UConn Home and Garden Education Center 2022

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Dean of the College, Cooperative Extension System, University of Connecticut, Storrs. The Connecticut Cooperative Extension System is an equal opportunity employer and program provider. To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, Stop Code 9410, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964.