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.

A table displaying which months are best to sow, plant and harvest.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Plant
Plant

Do not Plant in January

Do not Plant in February

Do Plant in March

Do Plant in April

Do not Plant in May

Do not Plant in June

Do not Plant in July

Do not Plant in August

Do not Plant in September

Do Plant in October

Do Plant in November

Do not Plant in December

Harvest
Harvest

Do not Harvest in January

Do not Harvest in February

Do not Harvest in March

Do not Harvest in April

Do not Harvest in May

Do Harvest in June

Do Harvest in July

Do Harvest in August

Do Harvest in September

Do not Harvest in October

Do not Harvest in November

Do not Harvest in December

  • Average Yield

    30 large onions per 3m row

  • Spacing

    10cm apart

    30cm between rows

    leave tip showing

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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Onions and milder-tasting shallots are one of the easiest crops you can grow.

Growing onions from sets

planting-onion-sets-5

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.

watering-an-onion-crop-2

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.

Watch this 20-second video demonstration from our friends at olive magazine on how to chop an onion.

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.

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Organic tip

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

onion-setton-5

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