September is the hinge of the gardening year, and the garden tasks in September look both backwards and forwards. The summer harvest is still coming in, but the days are shortening, the nights are cooling, and the fall garden needs planting now if it is to feed you through autumn. The September skill is triage: harvest what is ripe, plant what will grow in cool weather, and let go of summer crops that have finished. This guide splits the work by zone band — cold zones 1–4, temperate zones 5–7, warm zones 8–10, and frost-free zones 11–13. Frost dates are given only as averages and ranges, never as exact dates for a particular place, and zones 11–13 are frost-free, so their calendar runs on heat and rain instead. Before you act on any timing here, check your local extension service for the frost dates and sowing windows that fit your area.
Cold zones 1–4: harvest, protect and plant for spring
In zones 1–4, average first frost dates fall roughly from mid-September to early October, so September is the last full growing month. Seed starting indoors is finished for the year, apart from herbs on a windowsill and microgreens for winter salads.
Direct sowing outdoors is limited to the fastest fall crops early in September: lettuce, spinach, radishes and turnips under cover, plus green manures on beds that have finished. Transplanting is fall lettuce, spinach and kale under cloches, set out early in the month and covered on cold nights. Pruning is light: deadhead flowers, cut back spent perennials, remove dead wood, and do not prune shrubs that flower on old wood. Fertilising is finished for the year outdoors: stop feeding roses and shrubs so growth hardens before frost, and feed only containers that are still cropping. Pest and disease watch means slugs on fall greens, cabbage worms on brassicas, and late blight on tomatoes — remove affected plants and do not compost diseased material. Watering is easing as temperatures fall, but keep watering fall crops and containers, water in the morning, and reduce watering as growth slows. Harvesting is the main job: tomatoes, zucchini, beans, corn, carrots, beets, potatoes, onions, herbs, apples, pears and plums, and our harvest date calculator can help judge when roots and squash are ready. See the potato growing guide for lifting and curing. Soil and compost work is central: add compost to beds as crops finish, sow green manures, turn the heap, and start collecting fallen leaves for leaf mould. Houseplant care changes in September: bring tender plants inside before the first frosts, check them for pests, wash leaves, and reduce watering and feeding as growth slows.
Temperate zones 5–7: fall planting, dividing and the main harvest
Zones 5–7, with average first frost dates generally from mid-October to early November, make September the fall-planting month. Seed starting indoors is for overwintering crops in zone 7: start onions and broad beans indoors late in the month, and sow herbs on a windowsill.
Direct sowing outdoors covers fall and overwintering crops: sow lettuce, spinach, kale, radishes, turnips, peas and broad beans, and sow green manures on empty beds. Transplanting is fall lettuce, spinach, kale and brassicas, set out in the evening and watered in well, with fleece ready for cold nights. Pruning is a good September job: divide and replant perennials, cut back spent growth, deadhead roses, and prune summer-flowering shrubs after they finish. Our pruning calendar covers the timing. Fertilising is light: feed fall crops, feed lawns for autumn growth, and stop feeding roses and shrubs so growth hardens. Pest and disease watch means slugs, cabbage worms, aphids on fall greens, and powdery mildew in cool, damp weather — check weekly and remove affected leaves. Watering is easing but still needed: water fall sowings and containers, water in the morning, and reduce watering as temperatures fall. Harvesting is abundant: tomatoes, zucchini, beans, corn, peppers, eggplant, carrots, beets, potatoes, onions, winter squash, apples, pears and grapes. Soil and compost work means mulching beds, turning the heap, adding compost, and sowing green manures. Houseplants come inside in September: check for pests, wash leaves, repot if needed, and place them in their brightest windows before the days shorten.
Warm zones 8–10: fall garden goes in earnest
In zones 8–10, average first frost dates run roughly from mid-November in zone 8 to late December or never in zone 10, so September is the main fall-planting month. Seed starting indoors continues for fall crops: start broccoli, cabbage, cauliflower, lettuce, spinach and herbs indoors for transplanting, and start fall tomatoes indoors early in September in zones 9–10.
Direct sowing outdoors is broad for fall crops: sow lettuce, spinach, kale, radishes, carrots, beets, turnips, peas, beans, broccoli and herbs, with succession sowings every two weeks. Transplanting is the headline job: set out fall tomatoes, peppers, eggplant, broccoli, cabbage, cauliflower, lettuce and herbs, watered in well and shaded on hot afternoons. See the broccoli growing guide and cabbage growing guide for spacing. Pruning is light: deadhead flowers, cut back spent summer growth, shape shrubs, and prune roses lightly for a fall flush. Fertilising is for fall crops: feed new transplants lightly, feed containers, and refresh beds with compost before fall planting. Pest and disease watch means cabbage worms on fall brassicas, aphids, whiteflies, slugs after rain, and fungal diseases in humid weather — check weekly and remove affected leaves. Watering is still a big job: water deeply in the morning, mulch thickly, water containers daily, and water fall sowings gently until established. Harvesting continues: tomatoes, peppers, eggplant, okra, squash, melons, beans, corn, herbs and sweet potatoes, with summer crops giving way to fall crops. Soil and compost work means preparing fall beds with compost, mulching heavily, keeping the heap moist and turning. Houseplants outdoors need regular water and feeding, and September is a good month to repot and divide them before cooler weather.
Frost-free zones 11–13: fall sowing and tropical harvests
Zones 11–13 are frost-free, so September has no frost dates to plan around. The work is heat, rain and disease watch, with fall sowing for cooler-season crops. Seed starting is direct for most crops, but keep starting tomatoes, peppers and eggplant in trays, and sow lettuce, spinach and herbs in the coolest, shadiest beds as temperatures ease.
Direct sowing covers beans, corn, squash, cucumbers, melons, okra, sweet potatoes, carrots, beets, lettuce, spinach and herbs, with succession sowings every two weeks. Transplanting is continuous: set out tomatoes, peppers, eggplant, basil, cucumbers and tropical fruit trees, and plant bananas, papaya and pineapples now. Pruning is shaping and tidying: cut back spent growth, shape fruit trees after harvest, and remove dead wood, always giving plants airflow. Fertilising is steady and light: feed vegetables every few weeks, feed citrus and fruit trees, and use compost tea for a gentle boost. Pest and disease watch is weekly and year-round: aphids, whiteflies, spider mites, caterpillars, fungal spots and fruit flies all need attention, and in September humidity makes fungal disease the biggest risk. Watering needs care in both directions: water deeply in dry spells, but make sure pots and beds drain freely in heavy rain. Harvesting is abundant: tomatoes, peppers, cucumbers, beans, leafy greens, herbs, citrus, bananas and papaya. Soil and compost work never stops: keep the heap hot and turning, add green waste, and refresh beds with compost. Houseplants outdoors need dividing, repotting and a check for pests and rot in humid weather.
Dividing perennials, collecting leaves and the September checklist
September is the best month to divide perennials in zones 5–10: lift overgrown clumps, split them with a sharp spade, replant the healthiest pieces and water them in well. It is also leaf month: collect fallen leaves, shred them with a mower, and pile them for leaf mould, which makes superb soil conditioner in a year or two. Check our seed-starting calculator for fall sowing dates, and keep a note of which varieties performed best this summer.
Frequently asked questions
What should I plant in September?
In zones 1–4, sow only fast fall greens under cover and green manures. In zones 5–7, sow lettuce, spinach, kale, radishes and broad beans, and transplant fall brassicas. In zones 8–10, sow and transplant the full fall garden: lettuce, brassicas, carrots, peas and herbs. In zones 11–13, sow warm-season and cool-season crops as temperatures ease. Check your local extension service for the windows that fit your area.
When should I bring houseplants inside?
Bring tender houseplants inside before the first frosts, when night temperatures start falling regularly: September in zones 1–4, late September to October in zones 5–7, and only on cold nights in zones 8–10. Check each plant for pests, wash the leaves, and place them in bright windows.
Can I plant garlic in September?
In zones 1–4, garlic is usually planted in October, after the soil has cooled. In zones 5–7, late September to October is the window. In zones 8–10, plant garlic in October to November, and in zones 11–13 garlic grows poorly without a cold period, so check your local extension service for varieties that suit your area.
What can I harvest in September?
In zones 1–4, tomatoes, potatoes, onions, carrots, apples and plums. In zones 5–7, tomatoes, winter squash, potatoes, apples, pears and grapes. In zones 8–10, tomatoes, peppers, okra, sweet potatoes and melons. In zones 11–13, tomatoes, peppers, beans and herbs all month.
Should I divide perennials in September?
Yes, September is one of the best months to divide perennials in zones 5–10, because the soil is still warm and roots establish before winter. Lift the clump, split it into healthy pieces with roots attached, replant at the same depth, and water well.