How to plant an onion

Bulb onions are annuals which can be grown from seed or from sets of small bulbs. Onions are perfect to grow in well drained, fertile soil.
How To

How to plant onion seeds

Onions, both from seed and from heat-treated 
collections, are simple and cheap to produce. Bulb onions will need a long growing season if large onions are required or if you are planning to store them.

Choosing the best time to plant onions

The majority of onion sets should be planted in early spring, but some sets can be planted in autumn. Please check the supplier’s recommendations for planting season.

Sowing onion seeds

Sow the seed thinly about 1cm deep in rows about 9-12 inches apart. For larger onions, thin out the seedlings approximately 2 to 4 inches apart. The tip should just appear above the soil.


These vegetables need very little water, but ensure the onions are kept weed-free.

How long do onions take to grow?

Onions sown in spring will take between 12 to 18 weeks to grow, whilst onions sown in the summer will take up to 42 weeks. Lift the onions from the ground when needed.

How can I keep onions fresh?

Onions can be stored in nets and plaits or packed carefully in boxes.

How can I dry onions?

If it is sunny, leave the plants out to dry for about ten days. The plants need to be kept off the ground for ventilation so place the onions on upturned seed trays or in nets.
In wet weather, onions can be hung in a greenhouse to dry. 

What is the best way to string up onions?

You can plait onions together using the dried onion leaves of each bulb. Plait them together to create a string that can be hung indoors for storage. If you are storing onions in a box, they need to be layered and well ventilated – a crate would be ideal. Storage life will vary from 3 to 6 months depending on the type of onion.

How should I store onions?

If you are planning to store onions, wait until the leaves die back and then lift all of the onions in the crop, the onions will need to dry before storage.