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What To Do In Your Garden This September

by Cheryl Spencer | Aug 31, 2018 | Get Growing, Maintain Your Garden

The (mostly) cooler weather and clear skies of September are a welcome change from summer’s intense heat. Although there’ll still be warm days to come, I enjoy relaxing on the porch in the cool of the morning, so I can take in the beautiful backlighting cast by the fall sunshine.

September is a great time to reflect on what went well this year, 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 tomatoes and less kale? Whatever your goals may be, start planning now.

September is a time for planning, and for doing. Here’s my list of what to do in your yard & 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.


sunstar in the corner of a fall garden

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What to Plant in September

  • Plant new shrubs and perennials now. They still have enough time to set down roots before the ground freezes. Choose plants that’ll attract hummingbirds, songbirds, and beneficial insects to your yard. But check plants carefully before purchasing them. The healthier a plant is, the more likely it’ll transplant well and survive through winter.
  • Sow seed of next year’s biennial flowers like foxglove, dianthus, and forget-me-nots.
  • Fill any gaps in your perennial beds with late-flowering plants like sedums, asters, solidago, or chrysanthemums. These will provide food for pollinating insects that visit your garden this autumn. Water any new plants well and monitor soil moisture. If the soil is dry over two inches down, it’s time to water.
  • Divide and replant spring-blooming perennials. Water them well to encourage healthy root development.
  • Refresh your annual containers and pots with cool-season flowers such as pansies, ornamental cabbage, and kale, chrysanthemums, or fall-blooming asters.
  • Dig up herbs such as rosemary, chives, thyme, and marjoram from your garden. Plant them in pots now for growing indoors this winter.
  • Get your indoor plants squared away for the upcoming winter months. See my full indoor plant checklist for September.
  • Spring is the best time to move small trees or shrubs. But if you must move them this year, wait until they change color or drop their leaves before digging them up and moving them to new sites. They won’t suffer as much transplant shock when moved.
  • Plant broadleaved and needled evergreens, by October 1st. Water them at planting time and each week until the ground freezes if there isn’t any rainfall or snow cover.
  • September is a great month to plant new trees. Most nurseries put their remaining trees and shrubs on sale this time of year. Choose healthy plants and avoid any that don’t look robust. Plant them at the right height. Dig the hole at least three times the width of the rootball. Plant the rootball slightly above grade, and don’t loosen the native soil under the rootball. Water at planting time. Check the soil moisture every week, and water every week until the ground freezes if there isn’t any rainfall or snow cover.

Click to download this post as a printable checklist so you’ll know what to do in your garden this September and every September.

Top 5 Vegetable Gardening Tasks for September

  1. Over the next 4-6 weeks, you’ll have an abundance of produce. Check your vegetable garden every day and harvest vegetables as they ripen. Pick warm-season crops like peppers and tomatoes as soon as possible. If an early frost threatens, cover these plants with frost fabric or light blankets. Don’t use plastic sheeting for frost protection.
  2. Harvest unripe tomatoes before the nights get cold. And ripen them indoors.
  3. Harvest late-season squash and early pumpkins near the end of the month.
  4. Harvest any cool-season lettuces, spinach, peas, radishes, or swiss chard you planted in August.
  5. Maintain good sanitation in your vegetable garden. Remove diseased and spent plants immediately. Compost only healthy plant matter. Don’t put diseased plants or weed seeds in your compost pile.

September Garden Maintenance

  • Start a compost pile if you don’t have one. Layer grass clippings, fallen leaves, yard waste (but no diseased plants or weed seeds) and kitchen scraps. Then, add a little moisture. Add more shredded garden debris as annuals and perennials die back.
  • If you already have a compost pile, aerate and water it. It should be as moist as a wrung-out sponge.
  • Monitor your plants for spider mites. Hose them off with a forceful spray of water. They’re delicate insects, and the force of the water will kill many of them.
  • Protect your landscape from wildfires. Cut down brush and weeds. Clean out debris from underneath shrubs and trees. Trim back dead branches on trees and shrubs. Remove any dead trees or shrubs within thirty feet from your house.
  • Gather leaves and pine needles for mulching. But don’t use flammable mulches like these next to a structure. Use gravel instead.
  • Water during dry spells. Leaf scorch is a common problem in hot, dry weather. Water-stressed plants are more susceptible to attack by insects and disease. Many plants will wilt or turn yellow without adequate water.
  • Water large trees and shrubs, especially evergreens, until the ground freezes hard. Evergreens to lose moisture through their needles all winter and need adequate water to avoid winter burn or desiccated needles. Mature trees have extensive root systems that are wide and shallow. Don’t just water them under the “dripline.” Tree roots can extend 100-150% of the tree’s height. Water them where their roots have likely spread.
  • Don’t cut back ornamental grasses. You and neighborhood birds will enjoy the feathery seed heads throughout the winter.
  • If needed, prune early spring-flowering shrubs to remove diseased and damaged branches. Be careful to preserve the buds.
  • Wait until October to fertilize any tree or shrub that looks like it might benefit from fertilizing — for example; it has stunted growth, has failed to fully flower or leaf out, or has undersized fruit or off-color foliage.
  • Keep frost blankets handy for late-month frosts that might kill tender flowers. They’re also useful for protecting the last few tomatoes left on the vines when frost is predicted.

7 September Flower Garden Tips

  1. Continue to deadhead and de-leaf all annual and perennial flowers to encourage additional blooms. Unless you want to save seeds, or let some self-sow.
  2. Remove and replace any annuals that are exhausted and no longer flowering.
  3. Remember to water your flowers if your rainfall is low this month.
  4. Don’t forget to weed to prevent a late-season weed takeover in your flower beds.
  5. Refresh your annual containers and pots with cool-season flowers such as pansies, ornamental cabbage, and kale, chrysanthemums, or fall-blooming asters.
  6. Collect ripe seeds from non-hybrid annual flowers. Store them in labeled envelopes.
  7. Leave sunflower, cosmos, zinnia, and marigold seedheads in place for birds to feed on during the fall and winter.
  8. Bonus tips: There’s a lot more to do in the flower garden this month! Get the rest of the tips in my free downloadable checklist, or read the post.

Lawn Care Schedule for September

  • Begin fall seeding or sodding of cool-season grasses. How to prepare your seedbed: pull any weeds, rake the ground, dethatch or core-aerify the area, fertilize, and then seed. Keep your newly planted lawn areas moist, but not wet. If you core aerate, don’t cover the holes with compost. The holes are the perfect germination chamber for the seeds.
  • Don’t cut newly seeded lawns until they are at least 2 or 3 inches tall.
  • If your turf begins to turn brown and lifts easily off the ground, you may have grubs chewing on the roots. Pull back turf and check for white, C-shaped larvae with black heads. If you have over 10 to 12 grubs in a square foot of soil, you must treat the lawn. You must properly time your application of insecticides. You can spot-treat small areas immediately with a recommended control or, wait until the third week of next June to apply imidacloprid. As temperatures become cooler in fall, the grubs will move further down in the soil, taking them out of reach of insecticides.
  • Core-aerate your lawn if you didn’t do this in the spring. Professional lawn services can run an aerator for you to remove plugs of soil and grass at regular intervals over your entire lawn. Leave the plugs on your lawn to decompose. They disappear within a few weeks. Core-aeration helps fix compacted soil, heavy thatch accumulation, and poor drainage in lawns. But avoid aerating your lawn if your soil is very wet. That said, proper hydration of the soil is critical for removing intact plugs. So water your lawn 2-3 days before the aeration is scheduled. If you topdress your lawn with compost now is the time to do it. It’s best to do this after aerifying.
  • Mid-month is a good time to apply fertilizer to your lawn. Choose an organic fertilizer with a 3-1-2 or 4-1-2 ratio. Moderate temperatures this month along with cool nights and adequate rainfall (or irrigation) will encourage grass growth, making September a good time to feed turf. Apply one pound of nitrogen per 1,000 square feet of lawn.
  • Don’t let your lawn dry out too much in September. Fall lawns are gearing up for winter survival. Your lawn won’t be able to store as much energy as it needs to if it doesn’t have enough water.
  • Keep on top of your lawn weeding chores this month. It’s a good time to pull perennial weeds. Their root systems will weaken over the winter and (hopefully) die.
  • Call to schedule your sprinkler blow-out for October, if you don’t do this yourself.

Garden Planning in September

  1. Order spring-blooming bulbs that you’ll plant later this month and in October or November. Daffodils are ok to plant late in September, but save the tulips for October planting.
  2. Order spring-blooming bulbs to pot up and force indoors over the winter.
  3. Order garlic to plant at the end of this month or in October.
  4. Assess areas in the garden that may need new or replacement plants next spring.
  5. Take notes and photos to plan next year’s plantings. Make notes now, so you remember what you planned when next spring rolls around.
  6. Make sure you’re stocked up on frost protection blankets. Frost is right around the corner, and you don’t want to miss the opportunity to extend your season by protecting plants from light frosts.
  7. Pick a dry day this month to test your soil if you didn’t do it in the spring. Don’t add amendments or fertilizers to your soil until you know what your soil needs. Get a soil test first.
  8. Shop for new fall clean-up tools, if you need them. Invest in a quality leaf rake, new garden gloves, a compost thermometer, leaf collection bins and a chipper/shredder.

Wildlife in Your September Garden

  • Keep cleaning and filling your hummingbird feeders until it’s been one week since you last heard or saw one. Don’t believe the myth that you need to take your feeders down to encourage them to migrate. Keeping your feeder up until they’ve migrated helps them, but doesn’t keep them around longer than they need to be.
  • Leave annual flowers like sunflower, cosmos, zinnia, and marigold seedheads in place for birds to feed on during the fall and winter. The same goes for perennial seedheads of coneflower, rudbeckia, goldenrod, and yarrow.
  • Clean and refill your birdbath daily.
  • Hang a birdseed bell in a place where you can see it from inside your house. It’ll attract small songbirds like nuthatches, chickadees, and finches. If squirrels or nuisance birds like starlings are a problem, hang it inside a bird feeder cage.
  • Put out suet for migrating birds who need the extra fuel for their long journey.
  • Spray deer repellants if deer are a problem in your neighborhood. Re-apply after it rains.
  • Protect tree trunks and new shrubs from deer (or elk) with metal fencing. Surround the trunk, keeping the fencing two feet away from the trunks of trees by using metal or wooden stakes to hold up the fencing. If deer are a seasonal nuisance in your area, you can remove the cages during the late spring and summer. Make a note in your calendar to put it back up in September.
  • Protect trees from rabbit and vole damage by erecting a wire cylinder made out of hardware cloth. If you’ve also put up fencing for the deer, you can attach the hardware cloth to the metal fencing. Bury the hardware cloth 6 inches below the soil.
  • Protect newly planted shrubs from deer (or elk) by creating a cage with metal fencing held up with metal or wooden stakes. Make sure the cage is 2-3 feet taller than the shrub or closed at the top with zip ties to prevent them from eating the top of the shrub.




Cheryl Spencer

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