Always knowing when to plant, prune, and harvest.
All you need is the right checklist.
What To Do In Your Flower Garden This September (Early Fall)
September is a great time to think about went well this year in your flower garden, and what changes you want to make next year. It’s also a gentle reminder to get things done in the garden before the ground freezes.
Take time to walk through your garden and make notes. What would you like to add? More spring bulbs? Plants that attract pollinators, or appeal to birds? More annuals you grow from seed? Whatever your goals may be, plan now.
September is a time for planning, and for doing. Here’s my list of what to do in your flower garden this month.
The checklist is geared toward growing zones 5 & 6, but you can adapt it to whatever zone you garden in by shifting it a couple of weeks either way.
Read my full disclosure.
- Continue to deadhead and de-leaf annuals to encourage additional flowers.
- Remove and replace any annuals that are exhausted and no longer flowering.
- Continue to water your annuals if your rainfall is low.
- Continue to fertilize your annuals, especially those in pots.
- When a killing frost blackens tender annuals that are still flowering, that’s the time to pull them.
- Refresh your annual containers and pots with cool-season flowers such as pansies, ornamental cabbage and kale, chrysanthemums, or fall-blooming asters.
- Collect ripe seeds from non-hybrid annual flowers. Store them in labeled envelopes.
- Leave sunflower, cosmos, zinnia, and marigold seedheads in place for birds to feed on during the fall and winter.
- Sow seed of next year’s biennial flowers like foxglove, dianthus, and forget-me-nots.
- If you have room to bring potted, tropical plants indoors over the winter, plan to condition them gradually to the indoor environment. And bring them indoors after nighttime temperatures have dropped below 55 degrees. Spray them with an insecticidal soap spray to prevent bringing bugs in with them.
- Continue to deadhead your perennials to encourage additional flowers. But Stop deadheading roses and allow hips to form. This helps roses slow down and prepare for dormancy.
- Toward the end of the month, leave perennial seedheads of coneflower, rudbeckia, goldenrod, and yarrow intact for birds to feed on during the fall and winter.
- Don’t cut perennials back to the ground until their leaves and stems have lost all of their green color. It’s fine to deadhead and de-leaf as needed, but don’t cut the entire plant back until it has died back.
- Water your perennial beds if your rainfall is low this month.
- Continue to weed, weed, weed to prevent a late-season weed takeover in your perennial beds.
- Fill any gaps in your perennial beds with late-flowering plants like sedums, asters, solidago, or chrysanthemums. These plants will provide food for pollinating insects that visit your garden in the autumn. Water any new plants well and monitor soil moisture. If the soil is dry over two inches down, it’s time to water.
- Stake chrysanthemums if they get floppy.
- Divide and replant spring-blooming perennials. Water them well to encourage healthy root development.
- Divide or plant peonies in early September. Plant peony “buds” or “eyes” no deeper than 2 inches below soil level. If you plant them too deep, they won’t flower.
- Unless perennial vines are very top heavy or have suffered damage in a storm, don’t prune them until early winter or spring. Pruning now can cause a new flush of growth that can weaken the plant. Remove any dead or damaged foliage, but save a full pruning for later when the plant is dormant.
- Lift gladioli, cannas, and caladiums when their leaves yellow, and before a frost hits. Store them in a cool, dry spot. Dahlias usually store better after a killing frost.
- Collect ripe seeds from non-hybrid perennial flowers. Store them in labeled envelopes.
- There is no need to fertilize perennials in the fall unless they’re showing signs of a nutrient deficiency. Not fertilizing now allows them to enter their normal dormancy period without a spike in vegetative growth.
- Top off your mulch. I buy it in bulk, which is cheaper than the packaged kind and eliminates the packaging waste. Many suppliers deliver. Top up mulch in all garden beds as you clean them up.