Growing onions from seed can give you a wider choice of varieties to sow including large or exhibition onions, autumn planting onions, salad onions, pickling onions, shallots and perennial onions. It is also the way that many exhibitors choose to grow their show specimens.
Onions normally need well drained, fertile soil. They also benefit from traditional crop rotations as it can prevent diseases like white rot. Sow them in soil that has been previously used for potatoes and other related plants.
In the autumn it is best to prepare the soil with plenty of well-rotted organic matter followed with a general fertiliser.
Although seeds can be sown directly into the ground, many prefer to sow seeds in cell trays filled with multipurpose compost as it reduces the risk of disturbing the roots. When growing onions in cell trays follow these simple steps:
- Soak the compost and sow one seed per cell 6mm deep.
- Cover each seed with a layer of perlite.
- Label and cover with a propagator lid and place in a propagator in a gentle heat (approx 15°C)
- Prick each seedling out when they are large enough to handle into small pots and continue to grow until well established.
Planting out
- Onions should be planted out in rows during March or April 10-15 cm between each plant and 37-45cm between each row.
- Compost should be level to the top of the rootball, firm gently and water.
- Water well during dry spells to help the swelling of the bulb.
- Watering should stop once leaves begin to turn colour or bend naturally.
- Keep the onion bed weed free throughout the life of the crop, but be careful not to disturb the roots or damage the bulb.
Harvesting your onions
- To speed up the drying process use a folk to lift the bulbs once the leaves have bent over naturally and the necks have shrivelled.
- If the weather is warm, simply leave the onions in a sunny spot to ripen for up to a week, before placing onto a drying rack.
- However, if the weather is wet, lift the bulbs and place them under cover to complete the ripening process.