How to Grow Onions and Shallots in the UK

Onions are one of the most rewarding crops a beginner can grow. You plant them as small bulbs in spring, more or less ignore them through the season, and lift a basketful of full-sized onions in summer that will keep in the shed for months. Shallots work the same way, only each one you plant multiplies into a clutch of smaller, sweeter bulbs.

This guide covers everything you need to grow both well in the UK: choosing between sets and seed, picking the right varieties, planting, looking after them, dodging the two main problems, and getting them properly dried so they store all winter. None of it is hard, which is exactly why onions belong in every first veg patch.

Why grow onions and shallots

Onions are a kitchen staple — most of us use them almost daily — so a homegrown crop earns its space in a way that, say, a single lettuce never quite does. A small bed will give you enough to cook with for months.

They are also genuinely easy. Onions ask very little once planted: a bit of weeding, the occasional water in a dry spell, and that is close to the whole job. There is no pricking out, no staking, no fiddly pinching. If you are still finding your feet, they sit comfortably alongside the other easiest crops for beginners.

Best of all, they store. Lift a well-grown, properly dried crop in late summer and good keeping varieties will see you through to the following spring from a cool shed or garage. Few crops give you that kind of return on a single afternoon's planting. Shallots earn their place too — prized in the kitchen for their milder, sweeter flavour, and just as easy to grow and store. Because they need so little fuss, onions also make a good, low-stress crop to grow with children — see getting kids growing.

Sets or seed?

You can start onions two ways, and for most beginners the choice is easy.

Sets are small, part-grown bulbs that you simply push into the soil. They are the reliable, low-effort route: quicker to bulk up, more forgiving of cold soil, and far less likely to fail. The trade-off is that sets cost more per onion and come in fewer varieties.

Seed is cheaper, gives you a much wider choice of varieties, and arguably produces onions that store a touch better. But it needs an early start — sowing indoors in the depths of winter — plus warmth to get going, and more patience overall.

If this is your first year, start with sets. We compare the two routes in full detail, including which gives bigger bulbs, in onions from sets vs seed. The rest of this guide assumes sets unless we say otherwise, with notes for seed-growers where it matters. Shallots, incidentally, are nearly always grown from sets.

Choosing varieties

There is more to onions than the brown ones in the supermarket. Here are dependable UK choices, grouped by what you want them for.

Maincrop onions (spring planted, for storing):

• Sturon — the classic beginner's onion. Round, golden-brown, a heavy and uniform cropper, and an excellent keeper. If you grow only one, grow this.
• Stuttgarter Giant — a slightly flatter, mild, well-flavoured onion with a long storage life. Widely sold and very reliable.
• Red Baron — the standard red onion, with deep colour and a sweeter bite. Good for salads and cooking alike, and stores reasonably well, though not quite as long as the brown sorts.

Shallots:

• Golden Gourmet — a Dutch-bred yellow shallot, large for a shallot, mild, and a superb keeper. Forgiving and high-yielding.
• Longor — a banana shallot with long, elegant bulbs and a refined flavour the kitchen loves. A little more of a specialist, but a treat.

Overwintering onions (autumn planted, for an early crop):

• Senshyu (sometimes Senshyu Yellow) — a Japanese-type onion bred for autumn planting. Sits over winter and gives you onions in early summer, weeks ahead of the spring-planted crop.
• Radar — another tough overwintering set that shrugs off a cold winter and matures early.

Overwintering varieties bridge the "hungry gap", but they do not store as long as maincrop onions — eat them through summer and rely on your spring-planted Sturon for the keeping crop.

Where to grow

Onions are not fussy, but they do reward you for getting a few basics right.

Sun. Give them an open, sunny spot. Onions need light to bulk up well — in shade they sulk and stay small.

Soil. Aim for firm, fertile, well-drained ground. Heavy, wet soil is the main thing to avoid, as it encourages rot. If your plot is sticky clay, raised beds or simply working in plenty of compost helps; our guide to improving your soil walks through it. A no-dig bed topped with compost suits onions very well, since it gives that firm-but-rich surface they like.

Not freshly manured. Don't plant into ground that has just had fresh manure dug in. Too much nitrogen pushes lush leaf at the expense of the bulb, and soft growth stores badly. Manure the bed the autumn before, or grow onions where a hungry crop grew last year. Well-rotted garden compost worked in ahead of planting gives the steady, gentle fertility onions prefer.

Rotation. Onions are alliums, the same family as garlic, leeks and shallots. Don't grow alliums in the same patch year after year — that is how soil-borne diseases like white rot build up. Move them around the plot on a three- or four-year cycle. The crop rotation planner makes this easy to keep track of, and it is worth reading how to start a vegetable garden if you are laying out beds for the first time. A few companion flowers tucked along the edge of an allium bed bring in pollinators and helpful insects without crowding the onions.

Planting sets

This is the satisfying bit, and it takes minutes. Wait until the soil is no longer frozen or waterlogged — mid-March to mid-April for spring sets in most of the UK, a little later in the cold north.

1. Prepare the bed. Rake the soil to a fine, level finish and firm it gently underfoot. Onions like a settled bed, not a fluffy one.
2. Space them out. Push each set into soft soil about 10cm apart, in rows 25–30cm apart. Shallots need a touch more room — around 15–18cm apart — because each one multiplies into a cluster.
3. Plant at the right depth. Set the bulb so just the tip — the wispy nose — shows above the surface. Don't bury them completely. They should look like a row of little soldiers with their heads just poking out.
4. Firm them in. Press the soil gently around each one so it is held but not buried, and water if the ground is dry.

Overwintering sets go in exactly the same way in September–October, while the soil is still warm enough for roots to establish before winter. Growing from seed instead? Sow indoors in modules from late December to February, keep them around 10–15°C for germination, then harden off and plant out the young seedlings in spring at the same spacing.

Growing on

Once your onions are in, the work is light.

Weeding. This is the one job that matters. Onions have thin, upright leaves that cast almost no shade, so weeds romp away and steal light, water and food. Keep the bed clean, weeding by hand or hoeing carefully and shallowly — onion roots sit near the surface and resent being disturbed. A thin mulch between rows keeps weeds down without smothering the bulbs.

Watering. Onions are fairly drought-tolerant once established. Water during long dry spells, especially while the plants are growing leaf in late spring and early summer, but don't drench them. Even, moderate moisture is the aim.

Feeding. If the bed was decently prepared they need little. A light dressing of general fertiliser in spring is plenty. Resist the urge to feed heavily — you want a firm, well-ripened bulb, not a soft, leafy one.

Bolting and white rot

Two things go wrong with onions more than anything else. Both are easy to understand and largely avoidable.

Bolting is when an onion sends up a flower stalk instead of fattening its bulb. A bolted onion has a tough, woody core and won't store — eat it soon. The usual trigger is stress: a cold snap after planting, or a hot dry spell, can convince the plant it is in danger and should rush to set seed. To reduce the risk, buy good-quality, heat-treated sets (heat treatment kills off the embryonic flower), plant into reasonably warm soil rather than cold wet ground, and keep growth steady with even watering early on. If you do spot a flower stalk, snap it off promptly — it won't fully reverse the damage, but it directs energy back to the bulb.

Onion white rot is the disease to respect. It is a soil-borne fungus that rots the roots and base of the bulb, with tell-tale fluffy white mould and tiny black specks at the base. The plants yellow, wilt and pull up rotten. There is no cure once it is in your soil, and it can linger for years, so prevention is everything: rotate your alliums, never replant in an affected bed, and be careful not to import it on cheap sets or borrowed tools. We cover the symptoms, what to do, and how to keep it out in full in onion white rot.

Harvesting, drying and storing

This is where a little patience pays off all winter.

Knowing when. From mid to late summer, the leaves naturally yellow and the tops flop over at the neck. That is the onion telling you it has finished bulking up. Wait for most of the row to go over of its own accord — resist bending the tops over yourself, an old practice that can actually shorten storage life.

Lifting. On a dry day, gently ease each onion up with a fork to loosen the roots, then lift it cleanly. Don't bruise or drop them; damaged bulbs rot first.

Drying (curing). This step is what makes the difference between onions that keep and onions that don't. Spread the bulbs out in a single layer somewhere warm, dry and airy — a sunny path, a greenhouse bench, or a sheltered rack in good weather. Leave them two to three weeks, until the skins are papery and the necks have dried right down to a tight, rustling crisp. If wet weather sets in, finish them off under cover.

Storing. Once thoroughly dry, store only sound, firm bulbs with no soft necks or damage. Plait them into traditional ropes, hang them in net bags or old tights, or lay them in shallow trays — anything that keeps air moving around each onion. Keep them somewhere cool, dark and frost-free: a shed, garage or cool spare room is ideal. Check the store every few weeks and pull out any that soften before they spoil their neighbours. Good brown varieties like Sturon will keep right through to spring.

Shallots are harvested and dried exactly the same way — lift the clusters once the tops die back, split them into individual bulbs, dry thoroughly, and store. Save a few of your best for replanting next year.

What you'll need to get started

You really don't need much for onions — they are about as low-kit as growing gets. Once you've understood the method above, these few things cover the job, and any good UK seed merchant will have them in stock at the right time of year.

If you fancy growing your own from seed for a wider choice of varieties, the merchants above stock those too — see onions from sets vs seed before you decide.

Where next

Onions are a brilliant first allium, and once you've cracked them the rest of the family follows naturally. The obvious next step is growing garlic, which is planted in autumn and lifted the following summer in much the same way — plant once, ignore, harvest, store.

You'll find more crop guides on the grow vegetables hub, and if you are still planning where everything goes, the crop rotation planner will keep your alliums moving safely around the plot year to year. Grow a row of onions this spring, dry them well, and you'll be reaching into a basket of your own all winter.