September Gardening Tips Month-by-Month

Gardening Tips for September


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Plants At Their Best in September

Anemone japonica
Aster novae-angliae
Aster novi-belgii
Liriope muscari
Sedum spectabile
Some maples

In September, the weather starts to moderate a little and with the cooler temperatures comes a renewed desire to get out in the garden. Here are some of the things to do this month:

Must Do

  • Bring summer vacationing houseplants back indoors before night temperatures fall below 55 degrees. Check carefully for hitchhiking pests and disease before putting them near other houseplants. Gradually decrease light to acclimatize plants and help reduce leaf drop.
  • Continue mowing the lawn, as needed.  Be sure to set the mower blade high to encourage taller grass that will crowd out weeds.
  • Continue watering flowers, shrubs, and trees if rainfall doesn’t reach an inch or more every week or 10 days. It’s important for plants to go into cold weather with adequate moisture.
  • Stop pruning and fertilizing to avoid stimulating new growth that may be killed by an early frost.
  • Dig up tender bulbs like dahlias, caladiums, cannas, and tuberous begonias after the first killing frost (hopefully this won’t actually happen until October).  Use a garden fork to avoid damaging tubers, corms, etc.  Air dry and store in dry peat moss or vermiculite.
  • Plant container-grown or balled-and-burlapped shrubs and trees. Mulch well and keep newly planted stock well watered until the ground freezes.
  • Plant herbaceous perennials and roses. Warm soil and cooler weather make for perfect planting conditions.
  • Continue to harvest herbs, tomatoes, beans, etc. If frost is forecasted, cover plants with blankets, newspapers, floating row covers, etc. (no plastic) to protect from light frost. Try the Planket Frost Protection Cover .
  • Lift onions, shallots, and garlic as they become ready (usually after the tops fall over and necks begin to dry).
  • Lift and store potatoes.
  • Remove raspberry canes after they bear fruit.

Should Do

  • Reseed bare spots or put in new lawns using a good quality seed mixture. Fall is the best time to repair lawn damage or put in a new one.
  • Start fall clean-up in the flower beds, cutting back anything that has finished blooming (unless you want to keep it for winter interest) or is diseased.
  • Dispose of diseased or pest-ridden plant material in the trash, wrapped in a plastic bag. Although these materials can be composted, this should only be done if you’re certain that your compost pile reaches hot enough temperatures to kill any pathogens or over-wintering insects/eggs.
  • Watch for frost warnings (we do occasionally get frost in September) and cover tender plants.
  • Feed plants in containers to keep them blooming through the end of the season.
  • Purchase or order spring bulbs. Start planting them toward the end of the month and through October. Planting bulbs too early can cause top growth to sprout before winter; allow four to six weeks for good root formation before ground freezes.
  • Transplant or divide perennials, such as peonies, daylilies, poppies, iris, and phlox. While many plants can be divided in the fall, some plants are best divided in spring. Find out which perennials to divide in fall.
  • Collect and compost fallen leaves, or mow over them and leave them to decompose.
  • Thin fall crops, such as lettuce and carrots, that were planted earlier. If you haven’t planted them yet, it’s not too late, although they’re not likely to get very large before the season ends.
  • Apply a layer of organic material to garden beds this month or next. This includes rotted or composted manure, compost, chopped leaves, or a slow-release organic fertilizer.

Nice To Do

  • Plants, such as tuberous and waxed begonias, impatiens, fuschia, and geraniums, may be dug from the ground or containers and repotted for indoor enjoyment during the winter. Cuttings also may be taken, rooted in a growing medium and repotted for the winter.
  • Dig and repot herbs growing outdoors, or take cuttings to pot up and grow indoors.
  • Begin stocking up on gardening supplies before they are removed for the season from retailers’ shelves. Pots, potting mixes, fertilizers, and other products may be harder to find later in the season.
  • If you use herbicides, early fall is a good time to apply broadleaf weed killers. Follow label directions and spray on a calm day to prevent drift.
  • Plant colchicums. These “fall-blooming crocuses” (they’re not actually crocuses, although they look very similar) will bloom later in the fall.
  • Prepare new beds now for planting next spring. The soil is usually easier to work in the fall and fall-prepared beds allow for earlier plantings in spring. Beds may be mulched with compost, chopped leaves, or other organic material during the winter, if desired.
  • Clean, disinfect, and store pots.

Note: The September gardening tasks described here are for gardeners in zone 6. Tasks may be done earlier, or later, if you live in warmer or colder areas.


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2 Comments on Gardening Tips for September

  1. Lara

    September is still quite hot here in the low deserts of California. I often have started to soon and fried plants because 110s return. This week is a great example we are looking at 110 and monsoon! (I’m praying for rain).

    I know little about succulents but maybe they could handle these temps? What’s your thinking?

    Thanks for all the great reviews and articles!

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