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What To Sow
Onion sets growing

Photo: Unsplash

Hardy — can tolerate frost

When to plant
onion sets in the UK

Push sets into the soil with the tip just showing. Easiest way to grow onions — skip seed unless you enjoy waiting.

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20wto harvest
10cmspacing
5°Cmin soil temp
hardyhardiness
Plan it for your plot

Work out your own dates

Starts from the recommended sow date for your area. Sowed on a different day, or planted out late? Adjust below and the harvest moves with it.

Using the UK-average last frost · 15 April · add your postcode to tune it

Sow11 March
Harvest from29 July

Growing journey

Last frost
Direct sow5w before frost
Harvest15w after frost

20 weeks from sowing to harvest

Get onion sets seeds

Thompson & MorganSarah RavenSuttons

Links may be affiliate links. We may earn a small commission at no extra cost to you.

What onion sets need

Full sun. Well-drained soil. Birds will pull them up, so net early on.

Spacing

10cm

10cm between plants · 20cm between rows

Space evenly in rows. Thin seedlings early to avoid crowding.

the varieties

Varieties worth growing

Sturon

common

The all-rounder that stores beautifully into winter. Push the sets in, leave them alone, and by summer you'll have golden globes ready for everything from a Sunday roast to a Tuesday stir-fry.

in the kitchen

French onion soup

Slice a mountain of onions, caramelise slowly in butter for forty minutes until deep golden. Deglaze with white wine, add beef stock, ladle into bowls, top with gruyere-laden toast, and grill until bubbling. Worth every minute of stirring.

find the seedsThompson & Morgan→Suttons→
Sturon— full guide →

Red Baron

uncommon

Deep red skin and pink-flushed flesh that makes everything look more interesting. Milder and sweeter raw than yellow onions, so it earns its place in every salad and sandwich.

in the kitchen

Red onion tarte tatin

Halve the onions, caramelise cut-side down in balsamic and butter, lay puff pastry over the top, bake until puffed and golden. Invert onto a plate. Dinner party sorted.

find the seedsThompson & Morgan→Suttons→
Red Baron— full guide →

Centurion

uncommon

Early maturing and a heavy cropper. The onion for people who want results sooner and more of them. Golden-skinned, firm, and stores well enough to see you into the new year.

in the kitchen

Onion bhajis

Slice thin, toss with gram flour, cumin, turmeric, chilli, and a splash of water. Drop spoonfuls into hot oil and fry until crispy and golden. Better than any takeaway.

find the seedsThompson & Morgan→Suttons→
Centurion— full guide →

Setton

common

A golden onion that stores longer than almost any other variety — well into spring of the following year. Round, firm, and with a strong flavour that mellows beautifully when cooked. The choice for anyone who wants to be self-sufficient in onions.

in the kitchen

Caramelised onion chutney

Slice thin, cook very slowly in butter and a splash of vinegar with sugar, thyme, and bay. Stir occasionally for an hour until dark, sticky, and sweet. Pot it up. Goes with everything from cheese to cold cuts.

find the seedsThompson & Morgan→Suttons→
Setton— full guide →

Good companions

Keep apart from

  • Peas
  • Broad beans
Full companion planting guide & chart →

When to sow onion sets

Direct sowMarchApril

Based on UK average frost date. Enter your postcode for exact dates, or find your city.

Seeds

Where to buy onion sets seeds

Thompson & MorganSarah RavenSuttons

Links may be affiliate links. We may earn a small commission at no extra cost to you.

Kit

What you'll need for onion sets

The stuff beginners wish they'd bought sooner.

Bird nettingAmazon

Birds pull freshly planted sets straight out of the ground. Cover for the first 3-4 weeks until they've rooted properly.

Onion drying rackAmazon

Onions need 2 weeks of curing in air and sun after harvest. A wire rack lets air circulate underneath. An old oven shelf works too.

Links go to Amazon. We earn a small commission at no extra cost to you.

Get your exact dates

Enter your postcode for personalised planting dates for onion sets.

Keep exploring

Other crops to grow

Broad beans

Pinch out the growing tips once the first pods form to discourage blackfly. They

Peas

Sow every 3 weeks for a continuous harvest. Pick regularly to keep them producin

Lettuce

Sow a short row every 2 weeks and you'll never buy a supermarket bag again. Pick

Spinach

Bolts the moment it gets hot. Best in spring and autumn. Pick little and often —

Radishes

The quickest crop you can grow — seed to plate in 4 weeks. Sow between slower cr

Carrots

Sow thinly to avoid thinning — the smell of crushed leaves is a dinner bell for

Beetroot

Each seed cluster produces several seedlings — thin to the strongest. Don't chuc

Potatoes (maincrop)

Plant a few weeks after earlies. Earth up as haulms grow. Harvest when foliage d

Potatoes (early)

Chit (sprout) seed potatoes on a windowsill before planting. Earth up as they gr

Kale

Gets sweeter after a frost. One of the hardiest crops — can harvest all winter.

Parsnips

Very slow to germinate (2-4 weeks). Use fresh seed every year. Sow radishes alon

Spring onions

Sow a pinch every few weeks and you'll have spring onions all season. Dead easy

Swiss chard

Beautiful and productive. Pick outer leaves and it keeps going for months. Rainb

Turnips

Harvest when golf-ball sized for the sweetest flavour. Leave them too long and t

Leeks

Drop seedlings into deep holes and just water in — no need to fill the hole. The

Broccoli

Cut the main head first and you'll get side shoots for weeks. Purple sprouting i

Cabbage

Different varieties for each season — spring, summer, autumn, and winter types.

Cauliflower

Fold outer leaves over the curd to keep it white. Cauliflower leaves are delicio

Brussels sprouts

Grow through summer, harvest from autumn through winter. Flavour improves after

Garlic

Plant individual cloves Oct-Nov, pointed end up, 2.5cm deep. Garlic needs a cold

Parsley

Slow to germinate (3-4 weeks) — don't give up on it. Soak seeds overnight in war

Strawberries

Plant runners in spring or late summer and you will be picking fruit the followi

Raspberries

Plant bare-root canes in winter for the cheapest option. Summer varieties fruit

Blackberries

Cultivated blackberries produce bigger, sweeter fruit than wild ones and are tho

Gooseberries

One of the easiest fruit bushes for UK allotments. Plant a bare-root bush in win

Blackcurrants

Blackcurrants are packed with vitamin C and make the best jam and cordial. Plant

Redcurrants

Beautiful jewel-like berries that hang in trusses. They tolerate more shade than

Rhubarb

Plant a crown in winter, do not harvest the first year, and it will reward you w

Sweetcorn

Plant in a block, not a row — they're wind-pollinated and need neighbours. Each

Courgettes

You only need 2-3 plants. Seriously. Pick them small (15cm) or they turn into ma

French beans

Dwarf varieties need no support. Pick every few days — once they start producing

Squash

Big hungry plants — give them space and feed them well. Leave to cure in the sun

Pumpkins

Limit each plant to 2-3 fruits for bigger pumpkins. Sit them on a tile or slate

Coriander

Bolts at the slightest excuse. Sow every 3-4 weeks, pick frequently, and choose

Rocket

Dead easy and fast. Gets spicier in hot weather — which is either a feature or a

Pak choi

Sow early spring or after midsummer — it'll bolt faster than you can blink in th

Fennel

Sow after midsummer for best bulbs — earlier sowings often bolt. Don't transplan

Celery

Sow seeds on the surface — they need light to germinate. Start early in a propag

Dill

Sow direct — dill absolutely hates being transplanted. Short rows every few week

Tomatoes

Pinch out side shoots on cordon types. Feed weekly with tomato feed once the fir

Peppers

Start early — they're slow growers. Pinch out the first flower to encourage bush

Chillies

Need heat to germinate — use a propagator or the warmest windowsill you've got.

Cucumbers

Outdoor varieties are tougher and easier than greenhouse ones. Keep picking and

Runner beans

Build a strong frame — they get seriously heavy. Pick every 2-3 days or they go

Aubergine

Start very early — January isn't too soon. Limit to 5-6 fruits per plant if you

Basil

Pinch out flower buds to keep leaves coming. Harvest from the top to encourage b