September Gardening Checklist: What to Do in the Garden This Month

September is one of my favorite months in the garden. Summer isn’t quite finished, but you can feel the shift beginning. The mornings are cooler, the light starts to change, and while plenty of flowers are still blooming and vegetables are still coming in, the garden is slowly moving into fall.

This month isn’t about tearing everything out and calling the season finished. There is still plenty to enjoy—and plenty we can do now that will make the garden healthier, easier to manage, and even more beautiful next spring.

From planting and dividing perennials to harvesting vegetables, refreshing containers, caring for the lawn, and starting to think about spring bulbs, here’s what I’m doing in the garden this September.

1. Keep Deadheading—But Not Everything

I’m still deadheading many of my flowering plants in September, especially anything that will continue blooming with a little encouragement.

Remove faded flowers from:

• Roses
• Dahlias
• Zinnias
• Cosmos
• Annual containers
• Any repeat-blooming perennials that are still producing flowers

But this is also the time of year when I start leaving some seed heads alone. Coneflowers, black-eyed Susans, sedum and other sturdy perennials can add so much texture to the fall and winter garden. Their seeds can also provide food for birds.

I’ve learned that the fall garden doesn’t have to look perfectly cleaned up. Sometimes leaving a little of it alone is actually better.

2. Clean Up Diseased or Damaged Plants

While I don’t do a major garden cleanup yet, September is a good time to remove anything that is clearly diseased, damaged or completely finished for the season. Remove yellowing or diseased foliage and pick up affected leaves around plants rather than allowing them to sit in the bed.

I also continue cutting out dead or broken branches as I find them.

What I don’t do is heavily prune healthy trees and shrubs at this point. I save major pruning for the appropriate season for each plant.

Think of September cleanup as editing rather than clearing the entire garden.

3. Keep Weeding

I know—we’re all ready to be finished with weeds by September. Unfortunately, they aren’t finished with us. A little weeding now can make a big difference next spring, especially if you remove weeds before they have a chance to set seed.

I concentrate on the beds, vegetable garden and areas around shrubs and trees. It’s one of those jobs that isn’t exciting, but I’m always glad I did it.

4. Divide and Move Perennials

Cooler September temperatures make this a great time to move or divide many established perennials.

If something has become too large, isn’t performing well in its current location, or you simply want to rearrange a bed, fall gives plants time to begin establishing roots before winter.

Some perennials that may be divided in fall include:

• Hostas
• Daylilies
• Garden phlox
• Coneflowers
• Black-eyed Susans
• Many ornamental grasses
• Irises
• Peonies

Try to do this earlier rather than later in the season so the plants have time to settle in before the ground freezes. And keep newly transplanted plants well watered.

5. Plant New Perennials, Trees and Shrubs

Don’t assume spring is the only good planting season. Fall can actually be a wonderful time to add new trees, shrubs and perennials because cooler temperatures reduce stress on the plants while the soil is still warm enough for roots to continue developing. Just remember that newly planted trees, shrubs and perennials still need regular watering. Cooler weather doesn’t mean you can forget about them.

6. Add Some Fall Color

By September, some of my summer containers are usually starting to look tired. Instead of replacing everything, I like to work with what still looks good and add a few cooler-weather plants around it.

Some easy choices are:

• Mums
• Pansies
• Asters
• Ornamental cabbage
• Ornamental kale
• Heuchera
• Small ornamental grasses

Even changing one or two plants can completely refresh a front porch or patio for fall. You can also tuck small pumpkins and gourds into containers later in the month for an easy seasonal update.

7. Start Thinking About Spring Bulbs

It seems strange to think about daffodils and tulips when the garden is still blooming, but September is when I start planning for spring. Look for:

• Daffodils
• Tulips
• Crocus
• Hyacinths
• Alliums

September is a good time to buy your bulbs while the selection is best, although in many colder climates you can wait until the soil cools later in fall to actually plant them. One thing I’ve learned with bulbs: plant more than you think you need. They always look better planted in generous groups rather than one bulb here and one bulb there.

8. Keep Harvesting the Vegetable Garden

The vegetable garden may be slowing down, but September can still be incredibly productive. Regularly harvesting tomatoes and peppers helps keep the plants productive as long as the weather allows.

Allow pumpkins and winter squash to mature on the vine whenever possible, but harvest them before a hard frost. And this is the month when I start watching nighttime temperatures a little more closely.

9. Plant a Few Cool-Weather Vegetables

You may still have time for another small round of vegetables. September planting depends heavily on your growing zone and expected first frost, so check your local dates before planting.

Fast-growing cool-season crops are your best option. Try:

• Leaf lettuce
• Spinach
• Radishes
• Baby greens

Even a small raised bed or container of lettuce and spinach can extend the garden season another few weeks.

10. Pull Finished Vegetable Plants

As vegetable plants finish producing, I start removing them instead of waiting until the entire garden is done. Healthy plant material can go into the compost.

Plants showing signs of disease should be removed from the garden rather than composted in a typical home compost pile.

Cleaning things out gradually makes the final fall vegetable garden cleanup much less overwhelming.

11. Save Seeds

September is also a great month to collect seeds from some of your favorite flowers. Let seed heads dry on the plant and collect them on a dry day. Depending on what you grow, you may be able to save seeds from:

• Zinnias
• Cosmos
• Marigolds
• Sunflowers
• Coneflowers
• Black-eyed Susans

Label everything before storing it—you might think you’ll remember what those little envelopes contain next spring, but trust me, you probably won’t! Store seeds somewhere cool and dry until planting time.

12. Give the Lawn Some Attention

Early fall is one of the best times to give a cool-season lawn some attention. The soil is still warm enough for grass seed to germinate, while cooler temperatures make it easier for new grass to establish without the stress of summer heat. September is a great time to:

• Aerate compacted areas of the lawn
• Overseed thin or worn spots
• Repair bare patches
• Test your soil and add lime only if needed
• Continue mowing as the grass grows
• Keep newly seeded areas consistently moist

I usually aerate our lawn in early fall and overseed any areas that are looking thin. Aerating helps loosen compacted soil and allows water, air and nutrients to reach the roots, while overseeding helps fill in bare spots and thicken the lawn before winter. This year we had a few extra areas to repair after having our driveway repaved, especially along the new edges. After adding fresh soil and a grass seed suited to our area, we covered the patches with a light layer of straw to help hold moisture and keep the seed from washing away. The most important part after seeding is consistent watering—keep the soil damp while the new grass germinates and begins to establish.

13. Keep Watering

This is an easy one to forget. Cooler September days make it feel like plants don’t need as much water, but established gardens can still become surprisingly dry—especially after a hot summer.

Pay particular attention to:

• Newly planted trees
• New shrubs
• Recently divided perennials
• Containers
• Fall vegetable seedlings
• Newly seeded lawn

Water deeply rather than giving plants frequent shallow watering.

14. Start Using Falling Leaves in the Garden

As leaves begin to fall, don’t automatically think of them as something that needs to be hauled away. Leaves are incredibly useful in the garden. You can:

• Add them to your compost pile
• Shred them with the mower
• Use shredded leaves around garden beds
• Allow some leaves to remain in appropriate areas of the landscape

Fallen leaves also provide winter habitat for insects and other beneficial wildlife, so the goal doesn’t have to be removing every last leaf from the property. I still clean up areas where leaves become too thick or messy—I just don’t feel like the yard needs to be completely spotless anymore.

15. Check Houseplants Before Bringing Them Inside

If you moved houseplants outdoors for summer, start paying attention to nighttime temperatures. Before bringing them back inside:

• Check underneath leaves for insects
• Inspect stems and soil
• Remove damaged foliage
• Wash or wipe down leaves
• Clean the outside of the pots

I would much rather spend a few extra minutes checking them outside than discover spider mites or another pest after everything has been moved indoors.

16. Take Pictures and Make Notes

This might be one of the most valuable things I do all year. Take pictures of your garden now. Make note of:

• Plants that became too large
• Empty areas that need something
• Plants you want to move
• Colors you want more of
• Plants that didn’t perform well
• Areas that need spring bulbs
• Plants you absolutely want again next year

By February or March, it can be surprisingly hard to remember exactly what the garden looked like in September. Photos make planning next year so much easier.

My September Garden Checklist

• Continue deadheading repeat bloomers
• Leave some seed heads for birds and winter interest
• Remove diseased or damaged foliage
• Keep weeds from going to seed
• Divide or relocate overcrowded perennials
• Plant new trees, shrubs and perennials
• Refresh containers with fall plants
• Buy spring-flowering bulbs
• Continue harvesting vegetables
• Plant quick-growing fall vegetables
• Remove vegetable plants as they finish
• Save flower seeds for next year
• Overseed or repair thin lawn areas
• Aerate the lawn if needed
• Continue watering new plantings
• Start composting or using fallen leaves
• Inspect outdoor houseplants before bringing them inside
• Take garden photos and make notes for next year

Enjoy the September Garden

September always feels like a little bit of both seasons in the garden. There’s still plenty to enjoy and harvest, but I’m also starting to notice what needs trimming, what needs replacing and what I want to do differently next year. I’m not ready for a full fall cleanup yet—I’d rather keep the flowers blooming, let the pollinators enjoy what’s left and slowly work my way through these September garden tasks as the weather cools.

If you’re following along with my garden month by month, you can also look back at my August Garden Checklist to see what I was working on at the end of summer. And for more ideas around the yard, take a look through my Outdoor Living & Gardens section for seasonal gardening projects, planting ideas and simple ways I’m keeping our outdoor spaces looking their best.

For now, I’m enjoying these last warm days in the garden while getting a few things ready for the season ahead. Next month, I’ll be sharing my October Garden Checklist, when it’s finally time to start planting spring bulbs, preparing for frost, finishing up the vegetable garden and getting everything ready for winter.

And remember—a beautiful spring garden really does start with a little work in the fall.