September Gardening Checklist: 22 Tips and To-Dos for the Pacific Northwest
September is the month my garden can’t decide what season it is. The dahlias and zinnias are still going strong, but the mornings have that first cool bite to them and the light shifts earlier every evening. Two seasons, one garden bed.
There’s still summer to harvest and plenty of fall to plant for. Pests dig in harder this time of year too, so a little vigilance goes a long way. Here’s everything I’m working through in my own zone 8b garden this month.
As an Amazon affiliate, I earn a commission from qualifying purchases at no additional cost to you. My blog also features other affiliate links for your convenience. Click here to read my privacy policy.
22 September Gardening Tasks for the Pacific Northwest
A complete checklist of September gardening to-dos for Pacific Northwest gardens (Zone 8b), from the last of the harvest to getting a head start on spring.
1. Gather the Last of the Summer Harvest
Pick what’s left of your summer crops before the weather turns. Harvest tomatoes, peppers, green beans, cucumbers, and zucchini now. Dig potatoes once the tops die back.
For onions, stop watering when the stems yellow. Once the tops flop over, pull them and let them cure somewhere dry and airy.
A Quick note about my garden
Most of the flowers I share here are grown from seed in our greenhouse and planted in raised beds and containers throughout our cottage garden.
2. Preserve What You’ve Grown
Don’t let the last of the herbs go to waste. Cut healthy stems of basil, oregano, thyme, rosemary, sage, mint, lavender, chives, and parsley to dry or freeze.
You’ll thank yourself in January when a taste of the garden goes into a pot of soup.
3. Collect Seeds for Next Year
Save seeds from open-pollinated or heirloom flowers and vegetables to plant next year. I’ve been glad more than once that I saved zinnia seed from a variety that later disappeared from the catalogs.
4. Share Your Seeds
Don’t keep them all to yourself. Sharing seeds with gardening friends, or joining a local seed swap, saves money and keeps neighborhood gardens diverse and pollinator-friendly.
5. Refresh Your Containers for Fall
Tired summer annuals look a little sad by September. Give your pots and window boxes new life with fall favorites like:
Clear out the spent plants, refresh the soil, and tuck in new cool-weather color.
6. Start Fall Crops
September is a great time to sow quick-growing, cool-season vegetables. Try broccoli, peas, carrots, cauliflower, garlic, spinach, cabbage, or lettuce.
Pro tip: Row covers extend the growing season and protect tender crops from an early frost.
SHOP For Row Covers
7. Sow Cover Crops
Think ahead to spring by planting a cover crop in cleared vegetable beds. Rye, crimson clover, vetch, and fava beans prevent erosion and add nutrients back into the soil. I think of them as a cozy blanket for the beds over winter.
8. Plant New Trees and Shrubs
September is ideal for planting evergreens, trees, and shrubs. The soil is still warm, and roots have time to establish before the ground freezes. If your weather is running warmer than usual, wait until mid-to late September. Camellias, crape myrtles, and shrub roses all earn their keep with fall interest.
9. Prune and Tend Trees and Shrubs
Prune out any dead, diseased, or crossing branches. It tidies the plant, keeps disease from spreading, and encourages healthy new growth.
10. Give the Lawn Some Attention
Cooler weather makes September prime time for lawn repair:
11. Test Your Soil
A soil test tells you exactly what your garden needs, and what it doesn’t. Use the results to guide your fall fertilizing instead of guessing.
SHOP Soil Test
12. Apply Fertilizer Thoughtfully
A balanced fertilizer supports steady new growth through the cooler months. Spread it evenly over the soil before planting.
Go easy on nitrogen in fall. Too much pushes soft, fast growth that’s vulnerable to winter damage. A balanced feed keeps growth steady and sturdy as the cold sets in.
SHOP Balanced Fertilizers
13. Add Organic Matter
Working organic matter into the garden now pays off all next season. Add compost or well-rotted manure to improve soil structure and feed next year’s crops.
Mulching with fallen leaves helps too. I use leaf mulch to protect my dahlia tubers and other bulbs through winter.
14. Stay Ahead of September Pests
September is prime time for aphids, spider mites, and slugs in the Pacific Northwest. Keep an eye out, and take action before they get comfortable.
SHOP Insecticidal Soap Spray
SHOP Sluggo
15. Remove Diseased Growth
Powdery mildew runs rampant in September, so pull any infected or diseased leaves right away to keep it from spreading.
Powdery Mildew Prevention and Treatment
Remove infected leaves as soon as you spot them. Prevent it by spacing plants for airflow and watering at the base. A baking soda spray (1 tablespoon baking soda, 1/2 teaspoon liquid soap, 1 gallon of water) can also help.
16. Keep Up With the Weeds
Weeds don’t take September off. Stay on top of them so they don’t steal water and nutrients, and so they don’t snowball into a much bigger chore later.
A layer of mulch keeps new weeds down. Pull the ones that do come up by hand, getting the whole root. Weed after a rain or a deep watering, when the soil is soft. It makes the job so much easier.
Garden Supplies and Tools
Check out my favorite garden supplies and tools for the growing season. Whether you’re looking for potting soil or deer repellent, you’ll find what I use in my own garden.
17. Divide and Transplant Perennials
To keep perennials healthy and vigorous, dig up and divide clumps that have gotten too large. Replant the sections in well-prepared soil with room to grow.
Good candidates for fall division include:
18. Deadhead Spent Blooms
Deadheading your annuals and perennials keeps them blooming longer. Snipping off faded flowers redirects the plant’s energy into more blooms or healthier roots, rather than setting seed.
19. Order Spring Bulbs to Plant This Fall
If you haven’t already, order your spring bulbs now: tulips, daffodils, crocus, and hyacinths for planting later this fall. They’ll pay you back with a colorful show come spring.
20. Keep the Garden Watered
Don’t put the hose away yet. Keep watering deeply until the fall rains settle in. Dry soil heading into winter stresses plants more than the cold does.
21. Move Tender Plants Indoors
Before nighttime temps dip below 50°F, bring in tender plants like geraniums, fuchsias, and begonias. Repot if needed before moving them to a bright window.
Check for Pests First
Rinse or wipe the leaves before they come inside. The last thing you want is to bring aphids in with them.
Easy Houseplants to Add This Season
Snake plants, pothos, and peace lilies are low-maintenance choices that brighten indoor spaces through fall and winter.
22. Start Planning Next Year
Jot down notes about how the garden performed while it’s fresh in your mind:
Sketch out a few ideas now. Future you, standing in the garden next June, will be grateful.
Let’s Plan Your Dream Garden With Our
Gardening Planner
Unlock Your Garden’s Potential.
Our 35-page Ultimate Garden Planner is designed to help you organize, track, and flourish in your gardening endeavors.
Get yours for $4.99
Common Questions About Gardening in September
Not at all. Quick growers like lettuce, radishes, and spinach can still give you a fall harvest in the Pacific Northwest, especially with a row cover to buy a little extra time.
Sow cool-season vegetables like broccoli, peas, carrots, cauliflower, spinach, cabbage, and lettuce. It’s also the time to plant garlic, evergreens, trees, and shrubs while the soil is still warm, and to order spring bulbs for planting later this fall.
Yes. Garlic, shallots, and overwintering onions all benefit from a fall planting. Check with your local extension service for recommendations tailored to your exact spot in the Pacific Northwest.
Start preparing your garden for winter by clearing out spent plants, weeding thoroughly, and adding compost or mulch. Prune dead branches and consider a cover crop to protect your soil. These steps set you up for a smooth start next spring.
Final Thoughts for September Gardening
September is a month of transition, but it’s far from the end of the show. Between the harvesting, planting, dividing, and tidying, there’s still so much happening outdoors, and every task you tackle now makes spring that much sweeter.
So enjoy the last of the blooms, keep up with the chores, and don’t forget to pause and take it in. If you blink, you miss something.
If this September checklist helped, pass it along to a fellow Pacific Northwest gardener who’s also juggling two seasons at once.
Until next time,
Happy Gardening!
I’m a self-taught hobby gardener. Everything I share on my blog is my opinion and what has worked for me.
MORE POSTS
For You To Enjoy
Follow Me for More Inspiration
I’d like to be able to start saving flower seeds. If you have the time, I’d love a to know how you save the seeds and where you store them. Thank you for your blog!
I always love seeing your garden. Living in the lower Midwest many plants here are starting to look “tired”, but the main harbinger of fall is the change in light. New shadows and shade during usual sunny times of the day. I try to leave my container plants out till “the end” because of the migrating hummingbirds. I need to collect seeds this year, especially the mini zinnias. Happy late summer, Kim.