Thompson & Morgan
how to grow onions and shallot guide

How To Grow Onions and Shallots

Onions and shallots are particularly easy to grow and make the perfect low maintenance crop for beginner gardeners. They won't take up much space either, so you can squeeze a row or two in between other crops or even grow them in wide containers.

It's surprising how many recipes call for an onion, and French cuisine positively relies upon the milder flavour of the shallot, so it's well worth growing your own supply.

Bulbs vs. Seed

You can grow onions and shallots either from seed or from onion sets (small bulbs). The main advantage to growing onions and shallots from seed is that seed are much cheaper. Seed grown onions and shallots also have the potential to produce larger bulbs as they can be sown in the greenhouse in winter, thereby extending the growing season. However will require a little more time and effort, as well as taking up valuable greenhouse space, so many people prefer to opt for sets which can be planted directly into the garden.

Heat treatment

Some onion bulbs are heat treated. This simply means that they have been specially prepared to help prevent bolting - something which tends to occur particularly among red varieties. This process extends the growth period of the onions which allows heavier yields to be produced.

What’s the difference between Onions and Shallots?

Shallots and onions are of the same family and share many characteristics. From a culinary perspective, Shallot bulbs are smaller and tend to have a milder flavour than onions. They are famed for their use in French cuisine but are slightly trickier to peel, so perhaps this is why the onion remains more popular in the UK.

The main difference in the garden is that shallots form in clumps or rings of bulbs whereas onions grow as individual bulbs. Regardless of this, they are planted and grown in exactly the same way.

onion shallot

Spring vs. Autumn planting sets

Onion and shallot sets are often sold as spring planting or autumn planting varieties. Traditionally shallots and onion sets are planted in the spring as the soil begins to warm. However when are planted in the autumn and overwintered outdoors, they can be harvested a little earlier than spring planted sets, just as your stored onion crops are beginning to run out. Planting in the autumn also allows the gardener to get ahead at a quieter time of the year.

Which variety to choose?

When it comes to onions and shallot varieties, there is plenty of choice, but here are a few of our favourites to get you started!

Onions: Description:
Onion ‘Ailsa Craig’ A giant onion for the show bench, but equally good in the kitchen.
Onion ‘Doux des Cevennes’ A heritage onion with a pale skin and delicate flavour when eaten raw, but becomes more savoury when cooked.
Onion Red Baron A beautiful dark red onion with eye-catching red rimmed flesh and a stronger flavour than most varieties.
Onion ‘Golden Ball’ A very popular and reliable white onion, giving heavy yields of golden-brown skinned, crisp, flavoursome bulbs.
Shallots: Description:
Shallot ‘Camelot’ Visually stunning, this is the darkest red-skinned variety available from seed producing individual small, white fleshed bulbs that will store extremely well.
Shallot ‘Pesandor’ These long, slender copper-skinned bulbs have a pink tinge through the flesh. Perfect for French cuisine.
Shallot ‘Eschalote Grise’ Rarely seen in Britain, this gourmet Shallot is prized in French cuisine for its intense and concentrated flavour.

How to plant onion and shallot bulbs

onion planting

Onions are not particularly fussy or demanding but they do prefer a sunny position and well drained soil. It’s well worth preparing the planting area several weeks in advance by incorporating some well rotted garden compost to improve drainage and soil fertility. Don’t be tempted to add any quantity of manure though as this contains much higher levels of nitrogen than your onions require. On particularly wet ground, try growing onions and shallots in raised beds or even in containers.

Plant shallot and onion sets in rows in any firm, well drained soil. Position the bulbs so that the tip of bulb is just protruding through the soil surface. Leave a space of 10cm (4") between each bulb, and 30cm (12") between each row. Shallots can be planted at a distance of 18cm (7") apart, leaving 30cm (12") between rows.

If necessary, a sprinkle of granular onion fertiliser can be applied around the base of each set as you plant them.

After planting onion and shallot sets it is a good idea to cover crops with a protective netting or fleece to prevent attack from birds and insects.

How to sow shallot and onion seeds

If you prefer to grow your onions and shallots from seed then these can be direct sown outdoors in spring as the soil begins to warm up. Sow seed thinly at a depth of 1cm (½") and a distance of 30cm (12") between rows on any firm, well drained soil in full sun. When large enough to handle, thin onion seedlings to 10cm (4") apart for medium sized bulbs, or at a slightly wider spacing if larger bulbs are required.

Alternatively you can get a head start by sowing onion and shallot seeds in the greenhouse or on a bright windowsill in winter. Sow them in module trays using free-draining, seed sowing compost. Place the trays in a propagator or seal them inside a plastic bag at a temperature of 10-15C (50-59F) until after germination. Once germinated, grow onion and shallot seedlings on in cool conditions until all risk of frost has passed and they are large enough to plant outdoors.

Growing onions and shallots

Onions and shallots are remarkably undemanding and require only occasional watering during particularly dry periods. However, you will need to hoe between the rows regularly to keep on top of weeds. Any flowers that appear should be removed immediately to prevent onions from bolting.

Harvesting onions and shallots

harvesting onions

Harvest onions and shallots from late June or early July, a week or two after the leaves begin to turn yellow. Choose a dry day to loosen them from the ground with a fork. After lifting the bulbs, leave them on the soil surface for a day or two until they have fully dried in the sun. Once dry, remove the top foliage and store them in a well ventilated, dry position. Onion and shallot bulbs can be easily stored in a cool dry place for several months.



Sue Sanderson

Written by: Sue Sanderson

Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.