When to plant onions?

Updated 4 November 2026 · By the Orto editorial team

Plant onions in autumn, if the soil drains, or in spring: in Valle d'Aosta sets go in during October, or you transplant in May from a March sowing, and in Umbria outdoor sowing is listed for November and December. In the south the date depends on the variety: Campania lists planting in summer–autumn, late winter and spring, and cold early in the crop sends the plant to flower.

When, by region

Window	North	Centre	South
Autumn	Sets in October, on drained, sheltered soil: harvest in June. Not in December: October, or wait for spring.	Outdoor sowing in November and December, from Umbria's calendar. If the soil is sodden, wait.	Summer–autumn is one of Campania's planting windows. In Sicily the month depends on the type of crop: the guide does not fix one.
Spring	Sow indoors in March, transplant in May. Direct sowing in May only in the lower valley. Higher up, sets are better: they finish sooner.	If autumn was missed, sow indoors in March and transplant in spring, as in the north. Umbria's fertiliser sheet lists sowings before 15 March as their own case.	Late winter and spring, depending on the cultivar and day length. Cipollotto nocerino is harvested from March to June.

Indicative months. Sodden soil rots the bulbs, and cold in the first weeks makes them bolt.

Northern dates are from Valle d'Aosta's Informatore Agricolo: transplant in April–May or in October, direct sow in May, and sow a seedbed in March for a May transplant. November and December outdoors, in the centre, are in Umbria's sowing calendar (ARPA), the same one already used for the December calendar. The south's three windows, and the Cipollotto nocerino harvest, are from Campania's guide. The wider picture is in the planting calendar.

Sets, seed, transplants

Sets are the short path. The RHS plants them about 2 cm (¾ in) deep, tip just showing, 10–15 cm (4–6 in) apart in rows 20–30 cm (8–12 in) apart. Birds pull them out until they root: fleece or netting until they have hold. In Valle d'Aosta the rows are wider, 30–60 cm, with plants 10–15 cm apart. Higher up, sets are preferred because the crop finishes sooner.

From seed, in the north, sow a seedbed in March and transplant in May. Direct sowing, then thinning, is given for the lower valley, in May. The RHS sows indoors from mid-winter to early spring, about 1.3 cm (½ in) deep, and outdoors from early to mid-spring once the soil warms. The packet's onion type matters more than the colour.

Why they bolt

In Campania and Sicily, low temperatures and short days in the early stages send the plant to flower, and the bulb stops. Planting too early, or a cold snap on seedlings that have just emerged, does more harm than waiting a couple of weeks. The RHS notes that sets bolt more readily than seed; heat-treated sets do it less. If a flower appears, cut it off: the bulb will not store well, but you can eat it fresh.

Soil, water, rotation

They want sun and soil that drains. Waterlogging brings rots: both Valle d'Aosta and Campania say so. The RHS advises against autumn planting where the soil stays heavy and wet in winter: start the sets under cover and transplant in spring. Water the soil, and don't drown the bulb: see watering.

In Umbria the rules forbid onions straight after onions, ask for at least 2 years between crops, and forbid onions after potato, beet, cabbages and other alliums. In Sicily the advice is not to return for 3–4 years. In a home garden, keep the longer gap. Potatoes and tomatoes are in when to plant potatoes and tomatoes. Garlic, a close relative, is in how to plant garlic. Carrot with onion is a traditional pairing: what is documented is in companion planting.

In the app

Every plant in the catalogue has its own sowing calendar, and weather alerts for your area help you judge whether to sow now or hold off.

Frequently asked questions

Should I plant onions in November or in March?

It depends on where you are, and on drainage. In Umbria, outdoor sowing is listed for November and December. In Valle d'Aosta, sets go in during October, not December, or you transplant in May. If the soil is sodden, wait for spring.

Sets or seed?

Sets are quicker. From seed, in Valle d'Aosta, sow a seedbed in March and transplant in May; direct sowing is for the lower valley. Higher up, sets finish the crop sooner.

Why did my onion flower instead of bulbing?

Cold and short days in the early stages, according to the Campania and Sicily guides. Sets, the RHS says, bolt more than seed. Waiting a couple of weeks does less harm than a planting caught by frost.

Can I plant them where potatoes were?

Not in Umbria: the rules forbid onions after potatoes, and ask for at least 2 years before repeating onions. In Sicily the figure is 3–4 years. Keep the longer gap.

Do onions grow in a pot?

Yes, in sun, in a pot that drains. On a balcony the compost wets and dries fast: don't leave the saucer full.