Growing Onions at the Allotment

Growing Onions at the Allotment

Onions are part of the Allium family and come in many varieties, usually sown as mini bulbs known as 'sets'. You can sow onions from seeds, however they are slower to grow and need more attention as seedlings.  They are though, less likely to bolt (flower). 

Onion sets can be sown outdoors during autumn or early spring for a late summer to autumn crop. To sow onion seeds indoors, start them off in trays during winter to be hardened off and planted outside in spring. Thin them out if need be.

To sow sets outside, plant approximately one inch deep and 8 inches apart in rows.  Planting them close together will result in smaller individual onions.

Onions have shallow roots, so it really pays to pre-treat your soil before-hand with good compost or well-rotted manure.  Potash also helps the onions as they will absorb less sulphur, which causes the onions to become so strong, pungent and eye-watering!

They will require watering during dry spells and to be kept weed-free. Do not over-water; particularly from mid-summer for spring planted bulbs as this can mean that they will not store as well. Overhead watering can cause fungal diseases too.

Weeds can swamp the onion plants if left in the ground to tower over them and take away the nutrients needed for the onions to grow healthily, resulting in a smaller bulb. Remove any flowers at the top of the stems as soon as they appear. These will also take the plant's energy resulting in poor growth.

Also keep an eye out for problems such as leaf rust and onion rot, rotting can affect the neck, roots and/or the bulb.

Once your onion leaves start to die off and droop later in the season you can gently pull them up to store, but they need to be dried out first. Wait until the skins go brown and crispy (the top stems too) and inspect individual ones for rot or fungi before storing. They should be stored in a dark, cool place in boxes or nets - something that allows the air to penetrate them.

Onions can be eaten raw or cooked in a variety of dishes and salads. 



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Growing Onions in Summary

Sowing Onions

  • Sow sets in early spring and autumn
  • Sow seeds indoors during winter
  • Prep soil with well rotted manure

Growing Onions

  • Do not over-water or water from over-head
  • Watch for fungal diseases and rot
  • Keep weed-free and remove flowers as they appear

Harvesting Onions

  • Pull up after the leaves have died off
  • Dry out until outer skins are brown and crispy (purple for red onions). 
  • Store in a dark, airy and cool place