What to sow and plant in September

These are the jobs that come round in September for a garden in the middle of England. If you garden in Cornwall you are roughly a fortnight ahead of this list; in the Highlands you are up to ten weeks behind it, and following a national calendar is how seedlings get killed by a frost that was always going to come.

September is the busiest harvesting month of the year and, at the same time, the last useful sowing window for anything you want to eat over winter. The two run into each other: the beds emptying out this month are the ones that need a winter crop or a cover in them before the light goes. It is also the month the first frost arrives in the coldest parts of the UK, so in the north the tender crops are already on borrowed time while southern gardens still have six weeks of growing left.

Sow and plant now for winter

This window is closing rather than opening, so these are jobs for early in the month rather than late.

Overwintering onion sets

Autumn sets can go in from this month, and want protecting from birds until they have rooted in (RHS). ‘Senshyu Yellow’ and ‘Keepwell’ are long-standing autumn varieties, harvested the following June (Garden Organic) — several weeks ahead of spring-planted sets (RHS onions).

Skip autumn planting if your soil waterlogs over winter, because the sets rot. Start them one per module in peat-free compost somewhere cool and bright instead, and plant out in spring (RHS onions). Plot’s onion sets guide models the usual spring-planted crop, so its dates are the spring ones.

Hardy winter salads and leaves

Keep sowing the crops that will overwinter — spinach, winter lettuce, rocket and salad leaves (RHS). Sow hardy spinach varieties in late summer to early autumn for picking in autumn and again in early spring; if it is still hot, wait a week for better germination, but do not leave it so late that the plants are not established before winter (RHS spinach).

Garden Organic’s September list is wider, and most of it is sown direct or in modules now (Garden Organic):

Lamb’s lettuce (corn salad) and land cress — both very hardy, and both usually come through a bad winter.
Winter purslane (claytonia) — sow direct until the end of the month.
Winter lettuce — for harvesting in November and December.
Oriental greens — pak choi, Chinese cabbage and mustards. Best raised in modules, as they resent root disturbance.
Winter radish such as ‘China Rose’ or ‘Black Spanish’, plus mooli, turnip, kohl rabi, chicory, chard, perpetual spinach and kale.
Peas — the last chance for an autumn crop, using a quick early such as ‘Douce Provence’ or ‘Meteor’.

Spring cabbages

Plant out spring cabbages sown in July or August, and net them or pigeons will shred them (RHS). They go out once they are 10–15 cm tall with five or six true leaves, spaced 10 cm apart and thinned to 30 cm in late February or March (RHS cabbages).

Green manures, and preparing for October

Bare ground loses nutrients over winter. Sow winter tares or Italian ryegrass to hold them and protect the soil, then dig in next spring — or, if you are no-dig, cover with cardboard six to eight weeks before planting (RHS).

Garlic goes in from mid-autumn and needs a cold period to bulb up at all, so September is when its bed gets cleared and prepared rather than planted (RHS garlic). The same applies to autumn broad beans, which want well-drained ground.

It is also the month to keep planting new strawberry beds.

The full lists for this month

These are drawn from Plot’s plant guides. They are the national version — the planner shifts every date to your postcode area’s growing zone.

Sow indoors or under cover

Nothing on the list this month.

Sow outdoors

Ready to harvest

Plant

Trees, shrubs, bulbs and perennials

Prune

Other September jobs

Mostly harvesting, and mostly about getting things in before the weather turns (RHS grow your own, RHS jobs for September):

Harvest apples and pears. Fruit dropping under the tree is the signal; cup an apple in your hand and twist upwards, and if it comes away easily it is ready. Plums and autumn-fruiting raspberries are ready now too.
Lift the remaining potatoes before slugs get into them, clear the top growth to cut next year’s blight risk, and avoid nicking the tubers so they store.
Watch the first frost date for your region. Tomatoes, courgettes, beans and basil will not survive one, so in the north the choice is to pick green and ripen indoors, or cover.
Cut back old blackberry and hybrid berry canes after fruiting and tie in the new ones. Finish tying in fan-trained fruit against walls.
Cut down asparagus once the foliage turns brown, then mulch with well-rotted compost.
Divide herbaceous perennials while the soil still holds warmth, so divisions root before winter.
Net ponds before leaf fall, and clean out cold frames and greenhouses ready for autumn use.
Keep watering in dry spells — it is what prevents blossom end rot in tomatoes, splitting in root crops and flower drop on runner beans.
Collect and dry seed from perennials and hardy annuals you want to sow again.

What not to sow now

Anything frost tender, and anything needing a long season: there is not enough light or warmth left for it to finish. If a bed is empty and you have nothing hardy to put in it, a green manure or a mulch is a better use of the space than a sowing that will not make it.

How much September shifts where you live

The table below is the annual picture for each growing zone, not a figure for this month alone: the last and first frost weeks are long-term regional averages, and the growing season is the gap between them. They are planning estimates built from Met Office regional averages and the RHS frost map — useful for choosing which week to plant, and not a forecast for your own garden. A frost pocket at the bottom of the plot, a south-facing wall or a city centre will all beat the zone. In the app, the ten-day forecast and frost alerts use your full postcode; these planning dates stay regional.

Where you are	Average last frost	Average first frost	Growing season
South West Coast and Cornwall	late March	early December	260 days
South Coast and Channel	late March	late November	240 days
Greater London (Urban Heat Island)	late March	late November	250 days
South East and Home Counties	mid April	early November	215 days
East Anglia	mid April	late October	195 days
Midlands and Lowland Wales	late April	late October	190 days
Wales and West Coast	mid April	mid November	210 days
Northern England	early May	late October	175 days
Scotland Lowlands and Central Belt	early May	mid October	165 days
Scotland Highlands and Islands	late May	late September	120 days
Northern Ireland	mid April	early November	205 days
Channel Islands and Isle of Man	mid March	early December	250 days

September jobs cross-checked against RHS grow your own: September, RHS jobs for September and Garden Organic: what to sow and plant in September, with crop timings from RHS spinach, RHS onions, RHS garlic and RHS cabbages. Regional frost dates are long-term averages, not forecasts for your garden.