Onions ready for harvesting

Onions – Grow Guide

Find out how to grow onions, with the help of our guide to sowing, growing, harvesting and storing.

Overview

Onions and milder-tasting shallots are one of the easiest crops you can grow. You can raise them from seed, but it’s so much simpler and quicker starting with sets (small onions) that you grow on to cooking size.
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Spacing: 10cm apart 30cm between rows leave tip showing

Avg yield: 30 large onions per 3m row

Growing onions from sets

Planting

You can plant onion and shallot sets in early spring or autumn; from an autumn planting, you’ll get earlier, heavier crops. Both like sun and a moisture-retentive, fertile soil, ideally with plenty of well-rotted organic matter such as garden compost.

It's worth looking for heat-treated sets, as the resulting plants are less prone to bolting (producing flowers). Bolting reduces the quality of the crop.

Rake over the soil to break down any large lumps. Plant the sets with the tips showing. Onions need room to swell, so space them 10-15cm apart, allowing 30cm between rows.

Cover with fleece or netting so birds can't pull them up.

Tending the crop

In spring, apply a nitrogen-rich fertiliser to autumn-planted bulbs to give them a boost. Water well during dry spells. Onions are shallow rooting, so hand weed instead of hoeing between the rows.

Harvesting onions

Autumn-planted sets are ready after 36 weeks, spring-planted sets after 20 weeks, but as soon as they’re big enough to use you can pick them. The leaves will droop over and turn brown when they’ve stopped growing.

Storing onions

Spread onions and shallots out on newspaper or racks to dry. They’re ready when their outer skins rustle when you touch them. Hang or string them in nets in a cool, dark, dry place. They should last for months.

Preparation and uses

Peel and chop onions for soups, stews, pickles and sauces. Use sweeter varieties raw in salads.

How to chop an onion - 20-second video demonstration from our friends at olive magazine.

Troubleshooting

Drooping yellow foliage is the first sign of onion fly larvae, but by then they'll already be eating their way through the bulb. You can protect crops by growing them under fleece.

Onion-neck rot can be a problem in wet summers. Telltale signs are brown marks and fluffy grey mould. Don't overcrowd when planting, and dry bulbs thoroughly before storing.

Organic tip

Keep plants safe from damaging onion fly by growing pungent parsley among your onions.
Onion 'Setton'
Onion 'Setton'

Onion varieties to try

  • ‘Red Baron’ – nice flavour, sweet enough for salads and superb grilled or roasted. A reliable cropper and it stores well
  • ‘Setton’ – a good keeper and easy to peel, with a strong but sweet flavour
  • ‘Snowball’ – the mild, succulent flesh is perfect for sandwiches and salads. The bulbs store well

Related content

Fact file: onions

How to identify onion white rot

Lettuces – Grow Guide

Vegetable seeds to sow in June

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