Autumn vegetable garden: what to sow and when to harvest?

In this article 8

Autumn is the most underused season in the vegetable garden. We harvest the last tomatoes, clear everything out, and close up until March — even though this is when winter harvests and the very first spring ones are prepared.

The determining factor is not the cold, contrary to popular belief: it is the length of the day. Below about ten hours of daylight, growth practically stops, regardless of the temperature. The entire autumn calendar follows from this.

The rule that governs everything

A plant sown in September must have reached most of its size by the end of November. After that point, it will hardly grow: it will wait, alive but dormant, and start growing again in February.

Two practical consequences:

Sow earlier than you think. A two-week delay that goes unnoticed in May costs an entire harvest in September.
Add time to the stated growing period. A lettuce that takes six weeks in June takes ten in October. Packet timings are calculated for the growing season.

A simple guide: calculate the species' normal growing time, then add one-third to one-half, and count back from mid-November. That gives you your sowing deadline.

The calendar, month by month

August — the decisive month

It's the month we forget, and it's the most important of the entire autumn. The challenge is the opposite of spring's: it is too hot for many seeds, and the soil dries out within a few hours.

To sow — lamb's lettuce, spinach, winter lettuce, Chinese cabbage, autumn turnip, winter radish, arugula, chervil, chard.
To plant — winter leeks, winter cabbages started in June and July.
The challenge — lettuce and spinach have thermal dormancy: above 25°C at soil level, they simply will not germinate. Two solutions: sow in the evening and water thoroughly, or pre-germinate the seeds for 48 hours in the refrigerator between two damp cotton pads.
Shade the seedlings with a board, fleece, or piece of cardboard during the first three days.

September — the comfortable window

Temperatures dropping, soil still warm, rain returning: this is the easiest month of the year for sowing.

To sow — lamb's lettuce, spinach, arugula, garden cress, winter lettuce, white onion, turnip, radish, mustard.
Green manures — this is the ideal time. Phacelia, mustard, clover, and rye on all cleared beds. See Sowing green manures.
To plant — strawberries, perennial herbs, and anything that benefits from taking root before winter.

October — the seedlings waiting for spring

To sow — lamb's lettuce (last window), spinach, broad beans, peas with round seeds, garlic, shallots.
Autumn broad beans and peas spend the winter as young plants and produce three to four weeks earlier than a spring sowing. This is one of the best gardening opportunities, yet it is rarely used.
Flowers — poppy, cornflower, California poppy, columbine: sown now, they will emerge in spring with a clear head start.
To plant — trees, shrubs, soft fruit, perennials. Autumn is by far the best planting season: the plant has winter and spring to establish roots before its first dry spell.

November — protect and cover

To sow — still possible under a cold frame: lamb's lettuce, watercress, arugula.
To plant — garlic (until December in well-drained soil), trees, and shrubs as long as the ground is not frozen.
Above all — cover all empty beds. Mulch, fallen leaves, or green manure already in place. Bare soil all winter loses nitrogen, becomes compacted by rain, and erodes.

The case of lamb's lettuce

This is the example that best illustrates the logic of autumn, and a question that comes up again and again.

Sown in late August — it develops while the days are still long, forms a beautiful rosette, and is harvested from November to January.
Sown in late October — it emerges, remains tiny all winter, and is harvested in February–March. This is not a failure: it is another, later harvest.

Sow both, two months apart, and you cover the entire lean period. Lamb's lettuce is also remarkably hardy and self-seeds if a few plants are allowed to go to seed.

Protect to extend the season

A few degrees gained can shift a harvest by several weeks.

Winter fleece — the best value for money. It raises temperatures by 2 to 4 °C and lets water and light through. Put it in place before the first frosts, not afterward.
The cold frame — even one improvised with an old window. It allows you to harvest lettuce and radishes all winter across much of France.
Thick mulch — 15 to 20 cm of leaves over leeks, carrots, and parsnips left in the ground. They keep perfectly well in place and can be harvested as needed.
Exposure — winter crops benefit from a south-facing position, at the foot of a wall that radiates heat at night.

Beware of the opposite extreme: under a fleece or in a closed cold frame, stagnant humidity encourages gray mold. Ventilate as soon as the temperature allows, and never place a fleece over wet foliage.

What to harvest, and when

Cultivation	Sowing	Harvest
Lamb's lettuce	August or October	November to March depending on the date
Spinach	August–September	October to December, then again in March
Winter lettuce	August–September	November to February under protection
Rocket, watercress	August to October	Six weeks after sowing, continuously
Winter radish	August	October–November, stores in a cellar
Winter leek	Planted in August	December to March, in the ground
Broad beans, peas	October–November	May, three to four weeks early
Garlic	October to December	Following June–July

The five autumn mistakes

Sow too late. This is the number-one mistake, and it cannot be made up for. August and September are the months that matter.
Forget about thermal dormancy. Lettuce and spinach do not germinate when the soil temperature exceeds 25°C. Sow in the evening, water, and provide shade.
Leave beds bare. Every cleared bed must receive green manure or mulch, without exception.
Pull up plants at the end of the growing season. Cut them at ground level and leave the roots in place: they feed soil life and leave channels behind. See The basics of living soil.
Clean everything up. Hollow stems and dried flower heads shelter beneficial insects over winter. Leave some standing until spring.

Frequently asked questions

Can you still sow in November?

Yes, but only very hardy species, and you must accept a late harvest: lamb's lettuce, watercress, broad beans, peas, garlic. Under a cold frame, the window widens slightly.

Do you need a cold frame or a greenhouse?

No, but it makes a big difference. A simple frost cloth is enough to extend most crops by several weeks. A cold frame, even a makeshift one, allows you to harvest all winter.

What should you do with beds that remain empty?

Green manure if it's September, then a thick mulch. Never leave the soil bare: bare soil all winter means a total loss of fertility.

Do autumn vegetables have less flavor?

For many of them, it's actually the opposite. Cold triggers the conversion of starch into sugars—which is what makes carrots, parsnips, cabbages, and leeks noticeably better after the first frosts.

Should you water in autumn?

In August, yes—and abundantly: this is the main constraint when sowing at this time of year. From late September onward, rainfall is generally sufficient.

Key takeaway

Everything is decided in August and September: after that, day length stops growth, and your seedlings will have to wait until spring. Sow earlier than your instincts suggest, increase growing times by a third, cover every cleared bed—and don't forget October broad beans and peas, which will give you a month's head start in May.

For further information

Discover our autumn sowing collection and our green manures—to sow as soon as summer beds are cleared.