Gardening with Children

School Zone

Know, Sow and Grow your own Onions this year

Date Posted: 01 March 2014

 Onions are one of the most versatile and widely used culinary vegetables, they are easy to grow and can be stored over a long period so enabling you to eat your own home grown bulbs nearly all year round. They can either be grown from Seed or from Sets, onions prefer a sunny, well drained position, a Raised Bed is ideal.


Shallots are the upmarket version of the onion, although they are a lot smaller in size, it is said that they have a far superior flavour, widely used by chefs in restaurants they can be chopped up and added to salads or used whole in casseroles and stews, they are expensive to buy in shops yet they are easy to grow.

Shallots are best grown from sets, they require a little more space to grow, compared to onions, as each individual bulb will mature and split into a cluster of bulbs. Grow them the same way as onions (see below) but plant each set 15cm apart and allow 30cm between rows, in July when the leaves turn yellow lift the bulb clusters and separate them to allow each individual bulb to dry out thoroughly before storing them in net bags, in a cool dry place.

 Onions from seed

Growing from Seed

(check the seed packet as the growing instructions may differ for specific varieties)

Sowing Indoors

Onion seeds can be sown indoors between January and April. Sow seeds in trays of compost about half to one centimetre deep, water well and place in a propagator at a steady temperature of 15-20C (60-68F). When big enough to handle transplant into trays 5cm apart or into individual pots to grow on, then larger harden off before planting out 10cm apart, 23cm between rows.

Sowing Outdoors

In pre-prepared ground (when the soil is dry, apply and rake in a general purpose fertilizer, then tread over the soil lightly and rakeagain to leave a fine tilth) sow seeds outdoors, March to April, 1/1.5cm deep thinly in rows 23cm apart, water the soil before sowing. Germination can take between 14-28 days, when large enough thin plants to 10cm apart.

There is a much wider choice of onion varieties available from seeds compared to sets.

Onions from sets 

Growing from Sets

Onion sets are immature bulbs that have been specially grown for planting, buy heat treated varieties as these are less likely to bolt, onion sets are more reliable and are quicker to grow and mature than seed grown onions.

Plant onion sets outdoors in pre-prepared ground (when the soil is dry apply and rake in a general purpose fertilizer, then tread over the soil lightly and rake again to leave a fine tilth) in March/April, 10cm apart and 23cm between rows. Gently push the sets into the soil so that the tip is just showing then firm in the soil around them, take care when planting that you do not damage the base plate of the bulb this is where the roots will grow from. Birds often pull out newly planted onion sets, they say that they mistake the tops for worms, protect your onion sets with netting or fleece until the roots have formed they will anchor the bulb into the ground, carefully replant any bulbs that pop out of the soil.

If the ground is wet or frozen you can get your onion sets off to a good start indoors, plant individually in pots of compost, harden off then plant outside as above when the weather and soil conditions improve.

 Sprouting onion sets 9.5.12


Weeding is very important, weed between plants and rows carefully by hand or with a hoe, weeds will compete with onions for light and water and create a damp environment around the bulbs often leading to disease and poor growth. Water in dry weather and feed occasionally, remove any flower stems that appear this is called bolting and can be caused by a late cold spell or hot dry conditions.


When the bulb reaches maturity the foliage starts to turn yellow and falls over, when this happens leave them in the ground for another couple of weeks then on a dry day carefully harvest them by placing a fork under the bulbs and gently lifting them up, shake/knock off any loose soil. Spread the bulbs out on racks, trays or staging to dry out, outside if the weather is warm and sunny or indoors if it is wet, it can take up to 3 weeks for the bulbs to dry out sufficiently to be stored.

Onions on bench


Check the bulbs carefully, damaged or thick neck onions are not suitable for storing and can be eaten first. Store your onions instorage trays, net bags, tights or tie up into onions strings, place in a cool well-lit place, they should keep until late spring, as with any other stored fruits or vegetable check them regularly and remove any that show signs of going bad.


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