How to Grow Onions

Onions can be grown in two ways; from seed or onion sets. Onion sets are small onions that can be planted out in autumn (over wintering onions) or in spring. If possible, purchase onions sets that have been heat-treated as this will stop them running to seed.

OnionsFrom Seed
Sow the seeds in modules between late December and February, keep the compost damp and leave in a warm place. You can sow between four-five seeds per module and these generally don’t need thinning out. Plant out when they are big enough to survive on their own.

From Sets
Prepare the bed a couple of months before by adding manure and digging it in. Plant the sets in drills and cover so only the necks are showing. Keep well watered.

Harvesting and storage
When the leaves start to turn yellow, they can be harvested. Lay them out in a warm dry place for a couple of weeks so they can dry out. Make sure they are completely dry before storing. You can store onions either by hanging them in nets or plaiting them, or you can store them in boxes. Keep them in a dry dark place.

Pests and diseases
Onions should be rotated between different beds each year to prevent disease. Onions are prone to the following pests or diseases:

  • Onion neck rot
  • Onion white rot
  • Onion fly
  • Onion thrips

You can also help prevent disease by purchasing new fresh sets each year.

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