Laidback Gardening: What to Do in September?

September is a month between two seasons.

You can clearly feel that summer is coming to an end—vacations, long days, spontaneous swims, trout fishing—but we’re not quite ready for sweaters, Halloween decorations, and apple pies. 

In the garden, it’s the same thing: some plants are thriving as if it were the middle of July, while others are slowly beginning to turn red, sensing the change.

Should we speed up or slow down? Plant, harvest, divide, sow… or simply contemplate? It’s a bit of a “yes, no, maybe” kind of month.

Fortunately, the soil is still warm, but the nights are cooler, the days are beautiful but shorter, and there are many possibilities, none of which are urgent. It’s an excellent time to transplant, divide, sow green manure, plant bulbs, or quietly bring your houseplants indoors. No need to do everything at once, of course, as there will still be beautiful days in October. And above all, don’t clean up the garden (no, what an idea!).

Let the stems dry, the flowers go to seed, and the leaves fall where they will. Nothing is lost, everything is transformed. The cycle of life continues… in laidback fashion.

Vegetable Garden

1. Sow in September for a fall harvesber: Fall is great for growing leafy greens and root vegetables such as spinach and radishes, thanks to its cool nights and sunny days.
2. Planting garlic: September is a good time to plant garlic so that it can begin to take root before winter.
3. Harvesting herbs: Harvest and store herb leaves when flower buds appear. This is when they are most flavorful.
4. Harvest vegetables regularly: Harvest fast-growing vegetables such as beans and summer squash every 4 to 5 days. This encourages new growth and prevents them from becoming overripe.
5. Harvesting peppers: Pick them green for a mild flavor, or wait until they turn red for a sweeter taste.
6. Harvesting kiwis: Monitor the fruit of hardy kiwis and harvest them when the fruit begins to soften.
7. Harvesting corn: Pick corn as soon as the silks begin to turn brown.
8. Late harvest of hardy vegetables: There is no rush to harvest cabbages, Brussels sprouts, leeks, and Jerusalem artichokes, as frost improves their flavor.
9. Harvest summer squash while they are young: The smaller they are, the more tender and flavorful they are. And it encourages the plant to produce more!
10. Preserve your harvest: tomatoes, beans, cucumbers… now is the time to freeze, dry, or can while the abundance is there. After all, you can’t eat everything at once!
11. Ripening tomatoes indoors: Bring tomatoes indoors to finish ripening when nighttime temperatures drop below 43°F (10°C). Do not place unripe tomatoes in the refrigerator, as the cold will stop them from ripening.
12. Deadhead herbs: Removing flowers from herbs can stimulate leaf production and extend the harvest period for fresh herbs.
13. Invasive herbs: Herbs such as dill, anise, borage, chervil, coriander, and lemon balm can become invasive. Remove wilted flowers to prevent them from reseeding everywhere, or don’t and you’ll have a nice surprise next year!
14. Monitor watering of tomatoes: Never let your tomatoes run out of water, otherwise they may crack. Keep the soil evenly moist.
15. Decomposition of legumes: After harvesting, leave pea and bean plants to decompose in place. They naturally enrich the soil with nitrogen for future crops.
16. Cut back old raspberry canes: After harvesting, cut back canes with brown bark to make room for vigorous new canes, ensuring abundant fruit production the following season.
17. Consider sowing green manure: If a bed is freed up early, rather than leaving the space empty, you can sow buckwheat, clover, or oats to regenerate the soil before fall.
18. Frost protection: Be prepared to cover fragile vegetable plants if an early frost is forecast.
19. Remove diseased vegetables, but not the rest: leave the residue on the ground to nourish soil life… except in cases of visible fungal diseases (powdery mildew, downy mildew, black spots). In such cases, remove the severely affected leaves and throw them in the trash, not the compost.

Ornementals

1. Division and transplanting of perennials: Divide and move spring- and summer-flowering perennials during this season. Wait until spring for those that are in bloom.
2. Planting: September is a good time to plant new perennials, shrubs, or trees, as the soil is still warm, which promotes rooting before winter.
3. Plant late-season perennials: If a flower bed is lacking flowers in September, this is the ideal time to add fall-flowering perennials (asters, black-eyed Susans, heleniums, etc.). This is when you can clearly see where they are needed.
4. Watering after planting: Continue to water perennials, trees, and shrubs planted this year until the first frost to ensure they survive the winter.
5. Bringing annuals indoors: Certain annual plants can be preserved by bringing them indoors in the fall, either as seedlings or by taking cuttings, in order to protect them from the winter cold.
6. Buying fall bulbs: For the best selection, buy your fall-planting bulbs (tulips, daffodils, crocuses, etc.) as soon as they arrive in stores.
7. Protecting bulbs: To protect freshly planted tulip bulbs from squirrels, apply chicken manure or cover the soil with a piece of chicken wire after planting.
8. Reduce fertilizer use: Stop fertilizing your perennials or shrubs in September, as active growth has ended. Late nitrogen application could stimulate the formation of young shoots that will not have time to develop winter hardiness.
9. Late summer fungal diseases: It is common to see a little white (fungal disease) on ornamental plants. Slow its progression by spraying a solution of baking soda and insecticidal soap or accept the inevitable.
10. Deadheading: Deadheading annuals and perennials is not necessary, but you can do it to increase flowering. Keep in mind that many of them will produce seeds that will feed birds and may reseed themselves.
11. Remove unwanted suckers from the base of trees and shrubs: Remove suckers that appear at the base of shrubs and trees (lilacs, black locust, sumac, etc.) if you don’t want them to spread. You can also remove suckering plants and replace them with low-maintenance shrubs.

Lawn

1. Laying or overseeding a lawn: The best time to reseed or lay a lawn is in late August to mid-September, although it can also be done in spring. Lawns prefer warm soil, but cool fall temperatures and increased rainfall. However, if you sow too late, the young seedlings, which are not yet hardened off, could suffer from the first frosts.
2. Nematodes for white grubs: To treat infestations of white grubs (larvae of common and European cockchafers, Japanese beetles, and rose chafer beetles) in lawns, use nematodes, which are small parasitic worms. These nematodes penetrate the young larvae and inject them with bacteria that are toxic to them. Apply them between mid-August and mid-September, when white grubs have just hatched and the soil is relatively warm, between 21 and 30°C (70–86 °F).
3. Leave the clippings where they are: When you mow, leave the grass clippings on the lawn. They will decompose quickly and return nutrients to the soil. Less work, more fertility!
4. Tolerate weeds: Clover, plantain, dandelions, and other “weeds” are useful for pollinators and often withstand drought better than grass. A little diversity makes your lawn more vibrant and resilient!
5. Let birds do their thing: The birds that visit your lawn are your friends. They are looking for insects that harm your grass, including Japanese beetle larvae.
6. Topdress to naturally fertilize your lawn: At the end of summer, spread a thin layer of compost (1 to 2 cm) directly on the lawn. This is the best time to gently nourish the soil without chemical fertilizers. Topdressing improves soil structure, supports underground biodiversity, and prepares the grass to better survive the winter. Laidback bonus: let the earthworms do the work for you!
7. Differentiated mowing: Instead of mowing the entire lawn to the same height, allow certain areas to grow more freely—under trees, near hedges, or where certain plants are in bloom. Less maintenance for you, more food for pollinators, shelter for other insects, and a more resilient lawn.

Watering

1. Municipal restrictions: Follow your municipality’s watering restrictions.
2. Slow down watering at the end of the month: Towards the end of August, with cooler nights, the soil retains moisture better. Adjust your watering schedule: there is no need to water as much as during a heatwave.
3. Water new plants regularly: For new perennials, shrubs, or trees, it is important to water regularly during the first year, sometimes more for large trees. Why not install an automatic watering system with a soaker hose?
4. Try underground watering: Underground watering, carried out using water-filled tanks placed directly in the ground, moistens the soil deep down while preventing evaporation and wetting of the foliage. This promotes deeper rooting, limits leaf diseases, and reduces water use, especially during hot weather.
5. No need to water established plantings: Unless there is a prolonged drought, it is not necessary to water your permanent plants such as perennials, shrubs, and trees, especially if you have chosen plants that are suited to your conditions.
6. Avoid wetting the foliage to prevent disease: To prevent leaf diseases, try to water your plants without wetting their foliage. Leaky hoses water at ground level!
7. Water slow and deep: When you water, make sure the whole root zone is moist. Slow watering once a week is way better than quick, shallow watering every day. If your soil is sandy, water more often but for shorter periods to maintain moisture in the top 20 centimeters of soil.
8. Water early in the morning to save water: If municipal water restrictions allow, water early in the morning: this method is more efficient and uses less water than watering in the late afternoon.
9. Mulch to reduce watering needs: A layer of organic mulch (shredded leaves, straw, grass clippings, ramial chipped wood), even in pots, reduces evaporation, keeps the soil cool, and reduces the amount of watering needed.
10. Consider collecting rainwater: install a barrel under a gutter. Rainwater is free, soft, and at room temperature.

Compost

1. Take advantage of crop residues: September is an excellent time to enrich your compost with bean stalks, vegetable tops, damaged fruit scraps, etc. Chop them up coarsely to speed up decomposition.
2. Start storing dry fallen leaves: Even before they all fall, start setting some aside. They will be invaluable for balancing your compost rich in green matter (peelings, kitchen scraps).
3. Add green and brown materials alternately: For balanced compost, remember to alternate nitrogen-rich materials (peelings, fresh grass, weeds without seeds) with carbon-rich materials (dead leaves, newspaper, shredded cardboard). This promotes rapid, odorless decomposition.
4. Keep your compost moist, but not soggy: With the heat of June, compost can dry out quickly. Water it lightly if the material becomes too dry—it should have the texture of a wrung-out sponge to break down properly.
5. Stir your compost: Turn the compost every two weeks to speed up production.
6. No seeds or perennial roots: in summer, avoid adding weeds that have gone to seed or roots of invasive plants (dandelions, quackgrass, etc.), unless you have very hot compost (which is rare in domestic containers).
7. Avoid unpleasant odors: an ammonia or rotten egg smell indicates too much green material (nitrogen) or a lack of oxygen. Add dry leaves and stir!

Parasites

1. Pull up ragweed: This plant causes hay fever. Pull it up before it flowers to avoid allergies. Early removal also prevents the spread of seeds.
2. Cut weeds close to the ground to exhaust them: If you regularly cut weeds at ground level, they will become exhausted and eventually disappear. This causes less damage to the soil than hoeing.
3. Spray baking soda to prevent leaf blight: To prevent leaf diseases, spray the leaves of vegetables prone to blight (squash, cucumbers, beans, eggplants, peas, turnips, etc.) with a solution made from 1 liter of water, 1 teaspoon of baking soda, and 1 teaspoon of insecticidal soap.
4. Disinfect tools after pruning: To prevent the spread of disease, disinfect your tools after each use. This prevents the transmission of pathogens and keeps your plants healthy.
5. Treat white grubs with BTG: Bacillus thuringiensis galleriae is an effective biological treatment against white grubs, including Japanese beetle grubs. Apply it in August or early September, when the young larvae have just hatched and are still vulnerable. This natural product works by disrupting their digestive system—it is safe for humans, animals, and beneficial insects. Water thoroughly after application to ensure good penetration into the soil.
6. Watch out for the last caterpillars: In September, some caterpillars are still active, such as the tomato hornworm on tomatoes and eggplants, or the cabbage white butterfly on cruciferous vegetables (cabbage, broccoli, turnips). Inspect your plants regularly, pick off the larvae by hand if necessary, or install an insect net.
7. Let birds do the work for you: Less work: attract insect-eating chickadees, robins, and sparrows with a birdbath or a few berry bushes. They feast on caterpillars, larvae, and beetles of all kinds.

Wildlife

1. Let plants go to seed for seed-eating birds: Certain annuals and perennials such as black-eyed Susans, sunflowers, cosmos, and grasses produce nutritious seeds. Let them dry in place: goldfinches, sparrows, and juncos will love them.
2. Avoid pruning perennials too early: Several insects (solitary pollinators, lacewings, ladybugs) use hollow stems as winter shelters. Waiting until spring to cut back perennials helps preserve these natural shelters.
3. Hummingbird feeder nectar: Change the nectar in hummingbird feeders every week, or every three days when it is very hot. This prevents contamination.
4. Water is essential to life in the garden: Providing a source of clean water, even something as simple as a saucer or birdbath with a few stones, helps birds, insects, and small animals stay hydrated. Place it in the shade and change the water often to prevent mosquitoes. This simple act supports biodiversity, especially as fall approaches.
5. Clean your bird bath regularly: Rinse the bird bath every week (or every day during hot weather) with a strong jet of water. Once a month, clean it thoroughly with a vinegar solution (1 part vinegar to 9 parts water) and a brush. Avoid soap: it can damage birds’ feathers.
6. Welcome toads, your allies in the garden: Toads eat slugs, cutworms, Japanese beetles, and other pests. To attract them, provide them with a cool, shaded shelter (an upside-down terracotta pot or a pile of stones), avoid pesticides, keep a corner of your garden wild, and set up a quiet water source for them to breed.
7. Protect birds from cats: To protect birds in your garden, attach a bell or colorful collar to your cat’s collar. Place feeders more than 2.5 meters (8 feet) off the ground, limit access to the ground beneath feeders, and consider an outdoor enclosure (catio). Every little bit helps save birds!
8. Leave a wild corner: a pile of dead leaves, a few hollow stems, an old fallen tree trunk, or a slightly overgrown bush—all of these may seem neglected, but for local wildlife, they are a real refuge! Frogs, toads, solitary pollinators, and insect-eating birds find food and shelter there.

Houseplants

1. Bringing in houseplants: In colder regions, you may need to bring in your houseplants as early as August. When the nights start to drop below 10°C (50°F), that’s the time to do it. This prevents plants from suffering from the cold, and allows them to gradually acclimatize to the indoor environment before the arrival of cooler temperatures.
2. Avoid light shock: Plants that have enjoyed full summer sunlight may react strongly to the lower light levels indoors. Place them near a bright window at first, then adjust their position over the coming weeks depending on how they respond.
3. Repot certain indoor plants: If one of your plants seems cramped or the soil no longer retains water well, fall is a good time for light repotting. This is often the case with plants that have experienced rapid growth after spending the summer outdoors. Repot before the plants go dormant, which is often the case in fall or when they are brought indoors after several weeks outside. However, avoid repotting plants that are in full bloom.

And what do you do in your garden in September? Let us know so we can continue to improve the Laidback Gardener’s calendar!