This Month in Your Garden September 2023

Coastal Region – Christopher Burtt

  • Continue mowing the turf at a normal height until the nighttime temperatures begin to cool. Once it begins to cool, raise the mower height to allow more foliar growth in preparation for the first frost and dormancy.
  • Avoid applying fertilizer, especially any nitrogen, as this could increase disease pressure.
  • If concerned about winter weeds in warm-season lawns, an application of preemergent herbicide should be applied in the middle of September in preparation.
  • Deadheading of perennials and Annuals can be continued, and some perennials should be cut back after blooming. Cut back any overgrown perennials or herbs in preparation for overwintering.
  • Dividing and replanting of overcrowded perennials should be done at this time, such as bee balm, daylilies, and coreopsis.
  • Limit heavy fertilization, specifically nitrogen, for most plants. Always fertilize based on soil tests.
  • Many warm-season vegetables should still be harvested based on the individual species and the time in which they were planted. Sweetpotatoes should be ready to dig, and certain fruits, such as fig, should be ready to harvest.
  • Sow hardy annual seeds such as calendula, sweet alyssum, and larkspur.
  • Planting a second set of warm season crops can still be done, such as tomatoes, peppers, eggplants, squash, cucumber, and beans. Some fall crops are ready to be planted, such as broccoli, cauliflower, and kale.
  • Watch for fall webworms and armyworms as they become an issue quickly. Apply fungicide to camellias if flower blight has been an issue in the past. Clean up diseased leaves from hydrangeas and others to help with control of leaf spots.
  • Turf issues will include large patch and gray leaf spot. Be sure to only apply irrigation once a week (if needed) and do so in the morning. Irrigating too often is the biggest cause of disease pressure within most turfgrass.
Diseased Hydrangea.

Diseased Hydrangea.
Christopher Burtt, ©2023, Clemson Extension

Diseased St. Augustinegrass.

Diseased St. Augustinegrass.
Christopher Burtt, ©2023, Clemson Extension

Kale and parsley as ornamentals.

Kale and parsley as ornamentals.
Christopher Burtt, ©2023, Clemson Extension

Midlands Region- Jackie Jordan

September is a period of transition in the garden.

  • Take cuttings of warm-season annuals like basil, coleus, and geraniums to overwinter.
  • Plant seeds of hardy annual flowers like calendula, sweet alyssum, foxglove, larkspur, and poppies.
  • Freshen up containers and flower bed. Pull out warm season annuals and set out pansies, violas, snapdragons, and ornamental cabbage and kale once they become available.
  • Start shopping for spring flowering bulbs for the best selection. Bulbs can be stored in the refrigerator for several weeks until ready to plant. Just avoid storing bulbs near ripening fruit or vegetables.
  • There are a few fall blooming bulbs, like colchicum and autumn crocus, that are planted immediately and will bloom that season.
  • It’s time to plant collards, arugula, kale, mesclun, mustard, Swiss chard, broccoli, cauliflower, cabbage, and many other vegetables.
  • Plant cool-season herbs like chives, cilantro, dill, and parsley towards the end of the month.
  • Fertilize Tall fescue lawns at a rate of 1 lb. of actual nitrogen per 1,000 sq. ft. If your tall fescue lawn has become patchy from heat stress, make plans to seed at a rate of 6lbs. per 1,000 sq. ft.
  • Apply preemergent herbicides this month to control annual bluegrass. For preemergent herbicides to be effective, they must be applied before the weeds start actively growing. Annual bluegrass begins to germinate when we receive four consecutive days with daytime highs at or below 75 °F.
  • Another great way to prevent a lot of annual winter weeds is to freshen up mulch in your flower beds and maintain a 3-inch layer.
  • If you want to overseed your warm-season lawn with ryegrass, the middle of the month is a great time to do this, but be careful.
  • Early fall is a great time to divide perennials like daylilies, daisies, and hostas.
  • Fall is a great time to plant trees and shrubs. The plants have a chance to become established in the cooler weather and can take advantage of higher rainfall. If you have room in your garden, consider adding a native tree or shrub.
Johnny jump ups.

Johnny jump ups.
Amy Overbaugh, ©2023, Clemson Extension


Jackie Jordan, ©2023, Clemson Extension

Upstate Region- Barbara Smith

  • Apply preemergent herbicides to your lawn and landscape beds in mid- to late September to help prevent winter annual weed seed germination. Repeat application in 8 to 10 weeks for season-long control. Always read the label for application instructions, as The Label is the Law.
  • Mid to late September is the time for overseeding tall fescue, core aerating, and fertilizing. Be sure to get a soil test done to determine what fertilizer is best to use, along with lime recommendations, if needed.
  • Are fire ants the bane of your existence? Apply fire ant bait now to reduce the ant populations in the landscape.
  • Don’t be so hasty to clean up the flower seed heads. During the winter months, purple coneflower, black-eyed Susan, Agastache, and other perennial flower seeds provide an excellent food source for many songbirds. Also, many of these plants will self-sow.
  • September is a good time for garden record-keeping. Make notes in a garden journal of what grew well and what didn’t, so next spring, you can avoid any mistakes made during the past gardening season.
  • Now is the time to dig up and divide daylilies, iris, and many perennials.
  • Clean up summer vegetable garden debris to reduce insect and disease issues for next year. If you aren’t planting a fall garden, consider planting a cover crop to help build the soil for next spring.
  • There’s still time to plant your fall vegetable garden. Brussels sprouts, broccoli, carrots, collards, garden peas, kale, mustard, radish, spinach, and turnips are excellent cool-season crops to plant in September.
  • Harvest and dry herbs for use during the winter months; use your basil to make and freeze pesto.
  • Harvest your sweetpotatoes when the vines turn yellow. It’s important to dig them before frost as cooler soil temperatures will affect the quality of the potatoes.
  • Examine houseplants that spent the summer outdoors for unwanted pest hitchhikers. Treat any discovered pest problems before moving them indoors. Temperatures at or below 50 °F can damage many houseplants. Bring them in when outdoor temperatures are equal to comfortable indoor temperatures (around 68 °F to 75 °F). Your plants will acclimate better with the change.
During the winter months, purple coneflower (Echinacea purpurea) seeds provide an excellent food source for many small songbirds.

During the winter months, purple coneflower (Echinacea purpurea) seeds provide an excellent food source for many small songbirds.
Barbara H. Smith, ©2023 HGIC, Clemson University

In September, daylilies (Hemerocallis species) can easily be divided and replanted.

In September, daylilies (Hemerocallis species) can easily be divided and replanted.
Barbara H. Smith, ©2023 HGIC, Clemson University

It's time to harvest sweetpotatoes when the vines begin to turn yellow.

It’s time to harvest sweetpotatoes when the vines begin to turn yellow.
Barbara H. Smith, ©2023 HGIC, Clemson University

A plant in a pot Description automatically generated

Before bringing houseplants inside for the winter, carefully examine them for unwanted pest hitchhikers.
Barbara H. Smith, ©2023 HGIC, Clemson University

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

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