Every autumn the same message arrives: the winter lettuce looks perfect in October, sits there unchanged through November, and by January is exactly the same size it was three months earlier. Nothing has gone wrong. The plants have simply run out of daylight, and no amount of feeding, fleece or patience will change that until February.
Gardeners who grow through the winter work to a single number: ten hours. Below roughly ten hours of daylight a day, most vegetables effectively stop making new growth — they hold what they have, but they do not add to it. The American grower Eliot Coleman named that stretch of the calendar the Persephone period, after the goddess who spends part of each year underground, and it is the most useful piece of timing knowledge in the autumn garden. Here is where the wall falls in your garden, how to count backwards from it, and what is still worth sowing in the middle of September.
- The threshold Under 10 hours of daylight, growth slows to almost nothing
- At 52 °N Roughly 3 November to 7 February — Amsterdam, London, Berlin, Warsaw
- Rule of thumb A winter crop must be about three-quarters grown by 1 November
- What fleece does Buys temperature and protects leaves — it cannot add daylight
What the ten-hour rule actually is
Plants build tissue from light. As the days shorten, the total light a leaf receives falls away far faster than the temperature does, and somewhere around ten hours of daylight the amount a plant captures drops below what it needs to make meaningful new growth. It keeps its leaves, it stays alive, it may even sweeten as frost converts starch to sugar — but it stops getting bigger.
The dates depend entirely on your latitude, not on the weather. Around 52 °N — Amsterdam, London, Berlin, Warsaw — daylight drops below ten hours in the first days of November and climbs back through it in the first week of February: roughly thirteen weeks of standstill. At 56 °N, in Edinburgh or Copenhagen, the same window opens in the third week of October and does not close until the last week of February, which is four full months. Move south to Bordeaux or Milan and it shrinks to about eight weeks. Look up your own latitude once and write the two dates on the inside of the shed door; they are the same every year.
How to count backwards from the wall
If nothing grows after the first week of November, then everything you want to eat in December, January and February has to be nearly full size before that date. That turns a vague autumn worry into arithmetic. Take the days-to-maturity figure on the packet — our guide to seed packets and their terms explains where to find it — and then add roughly half again, because those figures assume long summer days and warm soil. A winter lettuce that claims sixty days in June realistically needs ninety from a September sowing.
Count that total back from 1 November and you have your last sensible sowing date. Ninety days back from 1 November is 3 August; sixty days back is 2 September. Which is precisely why the useful autumn sowing window feels so much shorter than the packet suggests, and why mid-September is the last call for anything you want to harvest as a full-sized plant rather than as baby leaves.
Planning an autumn sowing, step by step
- Find your two dates Look up when daylight at your latitude falls below and rises above ten hours. For most of northern Europe it is the first week of November and the first week of February.
- Add 50% to the packet's days to maturity Autumn days are shorter and soil is cooling, so nothing runs to summer schedule. Sixty days on the packet means ninety in practice.
- Count back from 1 November If the answer is a date that has already passed, either sow for baby leaves instead of hearts, or move the crop to a February sowing under cover.
- Germinate warm, grow on cool September soil is still warm, which is the one advantage of the month. Sow into modules in the light and plant out promptly — see how to germinate seeds.
- Cover for temperature, not for growth A cloche, cold frame or fleece keeps leaves clean and unfrozen so you can keep picking through the standstill. It does not restart growth. Season extension has the details.
Grown in time, or sown too late?
Sown in time
Three-quarters grown before the daylight drops below ten hours.
- You harvest from a standing crop all winter — a living larder, not a growing one
- Roots are established, so the plant shrugs off frost and wet
- It surges away again in February with a month's head start on spring sowings
Sown too late
Seedlings that meet the threshold at two or three true leaves.
- They sit unchanged for three months and give you nothing to cut
- Small, soft plants are the ones slugs and botrytis find first
- Many survive and catch up in spring — so it is a delay, not always a loss
That last point matters. Sowing late is not a disaster, it is a different plan: you are effectively making a February crop with an autumn sowing. Hardy leaves such as corn salad, spinach and rocket sown now will overwinter as small plants and then race away when the light returns, weeks ahead of anything sown in spring.
What still earns its place in mid-September
Three categories beat the clock. Fast, hardy leaves — corn salad, rocket, mizuna, mustard greens, winter purslane and hardy lettuce — reach picking size in six to eight weeks and are cut leaf by leaf, so they never need to be full-grown. Winter salad leaves beyond lettuce and our guide to winter lettuce cover both. Crops that use dormancy rather than growth — autumn-sown broad beans, peas and sweet peas, plus perennials that need cold stratification — are supposed to sit still over winter; the standstill is the point. And green manures: field beans, rye and vetch sown now make enough top growth to hold the soil together before the wall arrives, then wait. See green manures for autumn sowing.
What does not work is a full-sized heading crop. Cabbage, cauliflower, leeks, onions from seed, carrots for storing: all of them need light that September cannot promise. They belong to next spring's calendar, not this one.
Common mistakes
- Blaming the soil. Feeding a plant that has stopped for want of light achieves nothing, and excess nitrogen in November makes soft growth that rots.
- Expecting a heated greenhouse to fix it. Warmth without light produces pale, drawn, weak plants — see leggy seedlings.
- Harvesting a standing crop too hard. Plants cannot replace what you cut until February. Take a few outer leaves per plant, never the whole head.
- Sowing thickly to compensate. Crowded winter seedlings simply share the same light and rot together in the damp.
- Forgetting your latitude. Advice written for southern England is a fortnight out of date in Scotland and a fortnight early in Italy.
Frequently asked questions
Does the ten-hour rule apply to everything I grow?
It is a rule of thumb for leafy and fruiting vegetables, which is most of the kitchen garden. Roots already in the ground simply hold. Alliums and hardy brassicas tick over very slowly rather than stopping dead, and plants in a heated, lit propagator are outside the rule entirely — indoor microgreens and sprouts ignore the season completely.
Can grow lights get around it?
Yes, for seedlings and salad on a windowsill, and that is exactly why herbs on an indoor sill keep going. Outdoors it is not practical: you would need to extend daylight over the whole bed for several hours a day, every day, for three months.
When does growth actually restart?
When daylight climbs back past ten hours — early February at 52 °N — and it is startling how quickly it happens. Overwintered spinach and chard can double in a fortnight. That is also the moment to start sowing under cover again, so keep the sowing calendar to hand.
So is there any point sowing in late October?
Only for crops that are meant to overwinter as seedlings: hardy annual flowers, broad beans, peas, garlic and green manures. For anything you plan to eat before spring, mid-September is realistically the end of the line — and next month's list deals mostly with soil, cover and next year's beds.
Once you know your two dates, autumn stops being guesswork. Sow the fast leaves now, put the slow crops down for February, and treat November to January as a harvesting season rather than a growing one — while the warm-season beds come out and the greenhouse gets its autumn clean. If you are clearing cucumbers this week, our new guide to growing cucumbers from seed is the other side of the same coin: a crop that needs every hour of light the summer can give. Browse what to sow now, the full vegetable and herb ranges, or read on through our growing guides.
