Ask an older gardener in Slovakia, Czechia, Hungary or eastern Germany when to plant onions and you will often get the same answer: late October, once the ground has been turned. Not spring. The bulbs that come out of a bed planted that way are bigger, firmer and sharper on the tongue than anything from a spring sowing, and the method is old enough that most people who use it learned it from a grandparent rather than a book.
It also happens to be sound horticulture. Every step in it does something specific, and the reasons are worth knowing, because they tell you when to follow the method exactly and when your own conditions call for an adjustment.
A note on climate. The late-October timing below applies to temperate Central and Eastern European conditions, which is where this method comes from. If you garden elsewhere, the principle still holds but the date does not: find your own average first frost date and count back four to six weeks. There is more on adapting the timing further down.
The method, in brief
- Till or dig the bed and work in well-rotted manure, traditionally chicken manure.
- Plant onion sets in late October, once the ground has been prepared and the weather has turned cool.
- Space them 20 to 30 cm apart.
- Plant deep, around 10 cm.
- Do not water them in.
- Leave them alone until spring.
What follows is why each of those matters.
Why autumn instead of spring
An onion makes its bulb in response to day length. Once days pass a certain number of hours, the plant stops making leaves and starts moving everything it has into the bulb. That switch happens on the calendar, near enough, whatever the plant has managed to grow by then.
This is the whole argument for autumn planting. Bulb size is set by how much leaf the plant built before the switch. Each leaf feeds one ring of the bulb, so more leaves means more rings and a heavier onion.
A set planted in October puts down roots through late autumn, sits through winter, and starts growing leaves at the first mild spell, weeks before the ground is workable for spring planting. By the time a spring-planted set is finding its feet, the autumn one already has a head start it never loses.
The second advantage is water. Autumn onions do their growing while the soil still holds winter moisture, so they need far less irrigation and are less troubled by a dry May.
Timing: why late October
The window aims at a specific state: cool enough that the sets will not push up a lot of soft top growth before winter, mild enough that they still make roots.
Roots grow in soil down to about 5 degrees. Leaves need more warmth. Plant in late October and you get several weeks of root growth into a bed that is cooling, with little leaf. That is the ideal overwintering condition: anchored, established, not carrying tender growth into the frosts.
Plant too early, in September, and the sets grow tall and soft, then the first hard frost damages that growth and the plant spends its reserves recovering. Too early also raises the risk of bolting, where the plant reads the cold as the end of a season it has already lived through and runs to flower in spring instead of bulbing.
Plant too late, once the ground is cold or frozen, and there is not enough root growth before winter. Loose sets heave out of the ground as the soil freezes and thaws.
Adjusting for your own conditions. Late October suits the Central European climate the method comes from. Further north or higher up, move earlier, to the first half of October. In a mild maritime climate, November works. The rule that travels is this: plant four to six weeks before the ground normally freezes, so use your own first-frost date rather than the date on the calendar.
Use sets sold for autumn planting. Varieties bred for overwintering are far less likely to bolt than a spring variety put in at the wrong time of year.
Why the manure, and why chicken manure
Onions are hungry. They build a lot of leaf in a short window, and leaf growth runs on nitrogen. A bed that has been fed properly grows more leaves before the day-length switch, and more leaves is the whole game.
Chicken manure is the traditional choice, and the reason is its nitrogen content. It is markedly higher in nitrogen than cow or horse manure, and it releases it faster. For a crop whose size depends on building leaf quickly in early spring, that is exactly the right shape of feed.
There is a second, more particular reason. Onion pungency comes from sulphur compounds the plant assembles, and it needs enough nitrogen and sulphur available to do it. Chicken manure supplies both. The sharpness of onions from a well-manured bed is a real effect, not a story, and it is why the old gardeners insist on it.
The critical word is rotted. Fresh chicken manure will burn roots and can carry disease. It needs at least six months composting, until it is dark, crumbly and no longer smells of ammonia. Work it into the bed at digging, ahead of planting, so it settles before the sets go in.
If chicken manure is not available, well-rotted farmyard manure or good compost works, with a nitrogen feed in early spring as growth starts to make up the difference. What you should avoid is a high-nitrogen synthetic feed late in the season, which pushes soft growth that will not store.
Spacing: 20 to 30 cm
Wider than most packets suggest, and deliberately so.
An onion sizes to the room it has. Crowd the row and the bulbs compete for light, water and nutrients, and you harvest a lot of medium onions. Give each plant 20 to 30 cm and it fills the space it is given.
Spacing also moves air. Onions overwinter in cold, wet soil, which is the condition that downy mildew, white rot and neck rot all like. Air moving between plants dries the foliage after rain and dew and reduces the time spores have to establish. A tight autumn row is asking for disease in a way a tight spring row is not.
If you want a mix, plant at the wide spacing and pull every other one young as a spring onion. The remaining plants then get the full space for the second half of the season.
Depth: around 10 cm
This is deeper than spring planting, where sets go in with the tip showing at the surface, and the depth is doing three jobs.
Frost protection. Ten centimetres of soil sits above the freeze-thaw churn at the surface. A shallow set gets pushed out of the ground over winter and ends up lying on top of the bed with its roots exposed.
Stability. Deep planting anchors the set while the roots establish. Birds pull shallow sets out, and so does wind on a light soil.
Temperature stability. Soil temperature swings less with depth. The set sits in conditions that change slowly instead of following every cold snap and thaw, which is what triggers bolting.
Plant with the pointed end up and the flat root plate down. On heavy clay, plant slightly shallower, at 7 to 8 cm, because deep planting in soil that holds water raises the risk of rot. On light sandy soil, the full 10 cm is right.
Why you should not water them in
This is the step that surprises people most, because watering after planting is the reflex for nearly everything else.
The reasoning is straightforward once you see it. An onion set is a storage organ full of sugars and moisture, sitting in cool soil where nothing evaporates quickly and it will not be growing much for months. Autumn soil already holds moisture, and autumn rain will add more.
Water it in and you saturate the soil around a bulb that cannot use the water. Cold and wet together are the exact conditions for basal rot and neck rot, and a set that rots in November leaves a gap in the row you will not see until March.
Watering also settles soil tight around the bulb, driving out the air pockets that let it breathe and drain through winter.
The bed will be watered by rain, on a schedule that suits the season better than any hose. Plant into soil that is damp rather than dust dry, firm it gently by hand, and leave it. Start watering in spring, once leaves are growing and the plant is drawing on it, and stop again a few weeks before harvest so the bulbs firm up and store.
The same logic covers the rest of the winter garden: excess moisture around dormant plant tissue in cold soil is what causes losses. Our guide to protecting plants from frost works through the same reasoning for other crops.
Through the winter and into spring
From November to February there is nothing to do. The sets root, the tops may show a little green in a mild spell, and that is fine.
A light mulch of straw or leaf mould helps on exposed sites or in a hard winter, but keep it thin. A heavy mulch over onions holds water against the bulbs, which is the problem you avoided by not watering.
In early spring, once growth restarts:
- Firm back any sets lifted by frost heave.
- Weed thoroughly and keep weeding. Onions have thin upright leaves and cast almost no shade, so they lose badly to weeds.
- Feed with nitrogen if the bed was not manured in autumn, once leaves are growing.
- Water in dry spells through spring, then stop as the tops begin to soften and fall.
Harvest when the tops yellow and fall over on their own, usually a few weeks earlier than a spring-planted crop. Lift on a dry day and leave the bulbs somewhere airy to cure for two weeks before storing.
What you get
Larger bulbs, because the plant built more leaf before the day-length switch. Firmer bulbs that store better, because they grew steadily through cool weather rather than racing in summer heat. And a sharper, more pungent onion, from a well-fed bed with enough nitrogen and sulphur to build the compounds that give it its bite.
The method is old because it has been tested by people who could not afford a failed crop. Every part of it is doing something, and once you know what each part does, you can adapt it to your own ground without losing what makes it work.
If something does go wrong in the row, yellowing tips or patchy growth in spring can mean several different things, and onions rarely announce which. Photograph the affected plants in Gardenix and the app names the most likely cause with a confidence level, gives a health score and a treatment plan for that specific problem instead of general advice. It also warns you before a frost night and holds back watering reminders when rain is forecast. Your first 3 scans are free.