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Growing Onions

How to grow maincrop onions in containers, garden beds and allotments



Family/Latin Name

Allium  - cepa

Type of Plant

Bulb - Crop Rotation Group = Others

Suitable for

Garden Beds, Allotments, large containers

Pests & Diseases    Companion Plants    In the Kitchen

See also:-  Vegetable Growing Glossary  |    Container Growing  | Buying Seeds & Plants


Plant Dimensions

Height 60cm/2ft  - Spread up to 30cm/12"

Yield per 1.5cm/5ft row 2.2kg/5lb

Time between sowing and harvesting

Sowing Seed  - 24 - 40  weeks Depending on Variety

Planting Sets - 20 weeks

Where to Sow or plant sets

Outdoors in open ground or very large containers

Sowing or planting time

Seeds:  March- April  - temperature +10C/50F

Sets: Late September- October or March-early April

How to Sow/plant

Seeds - 12mm/½" deep - very thinly -  in rows 30cm/12" apart or in groups/blocks.

Sets - plant 15cm/6" apart in rows 30cm/12" apart or in groups/blocks.

After Germination

Seeds - Thin seedlings to 2.5cm/1".  Destroy thinnings as soon as possible. Keep the soil moist but not very wet and weed free.

Sets -   Keep the soil moist but not very wet and weed free.

Growing on - in Pots

As above

Growing on - in open ground

Seeds - thin to 10cm/4" apart. Destroy thinnings as soon as possible. Keep weed free. Water  in dry weather and feed once or twice during the growing season. 

Sets -  Keep weed free. Water  in dry weather and feed once or twice during the growing season. 


Break off any flower stems which may appear. Stop watering once the bulbs have swollen to full size and pull back any covering earth to expose the bulb surface.


Once the foliage has turned yellow and toppled over, leave the bulbs for a further two weeks to ripen then carefully lift with a fork.


Onions which are not going to be used immediately should be spread out and left to dry (outside if the weather is clement or inside if damp) for 7-21 days depending on the size of the bulbs.. Discard any soft or damaged bulbs.


Onions kept in a cool dry place will keep for up to 6 months.

Pests and Diseases

Companion Plants

Onion Fly
Indications Yellow drooping leaves and maggots in the base of the bulbs
Treatment None. Lift and burn infected plants
Prevention Organic
1. Practise crop rotation.
2. Destroy any thinnings or broken leaves
3. Firm the soil around young plants very firmly
Spray young plants with an insecticide containing chlorpyrifos
Stem and Bulb Eelworm
Indications Young plants leaves become swollen and twisted. Bulbs have a soft feel to them and often split at the base. The worms are not visible to the naked eye.
Treatment None - lift and burn infected plants
Prevention Practice crop rotation
White Tip
Indications Tips of leaves turn white and papery, spreading downwards
Treatment Organic
Lift and destroy badly infected plants
Spray with an insecticide containing Dithane as soon as you see the first signs of disease
Prevention Practice crop rotation
Downy Mildew
Indications Yellow patches on leaves with a greyish mould underneath
Treatment Organic
Remove the infected leaves and apply an organic copper spray/dust to diseased and surrounding plants every 7-10 day
 Remove the infected leaves and spray with Dithane at first sign of attack
Prevention Avoid damp or humid sites and overcrowding.
Practice crop rotation.


Companion Flower Graphic

Grow Beetroot, Carrot, Lettuce, Cabbage Family
 close by.



Create a bio-diverse environment by planting flowers nearby to attract bees, ladybirds and other "friendlies". 


To learn more about companion planting click here.

In the Kitchen

Storage:  Loose or in net bags for 2-3 weeks in a cool, dark, dry place.

Preparing:  Cut off the root then peel the papery skin off. It may be necessary to take off an extra "layer" to get to the  unblemished bulb.



Wedges  =  35-40 minutes  Coat with oil.


Wedges, sliced, chopped - Add to stews at the beginning


Sliced or chopped   =  10 minutes 


Sliced or chopped  =  3-5 minutes (225g/8oz)


See individual recipe


For more preparation and cooking information about onions plus lots of  recipes visit our sister site www.recipes4us.co.uk.

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