Grow your own: Onions

Push each set into the ground so the top is just showing

I prefer to buy loose onion sets, rather than those sold in packets, because it's cheaper to buy this way and I can select smaller, but not tiny, sets – large, plump ones are tempting, but prone to sending up flower stems.

I never plant the sets before early April – planting early while it is still too cold can lead to bolting – but it's wise to buy before that or stocks may have sold out. Heat-treated sets are said to give maximum performance, but I've never thought them worth the extra cost. 'Centurion', 'Red Baron' and 'Sturon' are superb varieties, all granted the Royal Horticultural Society (RHS) Award of Garden Merit (AGM).

I stand sets upright in a shallow tray, after snipping some of the dried tops off to prevent worms or sparrows pulling them up, and keep in a light, unheated place until planting time. I also plant a smaller number of autumn onion sets in late September to early October to fill the gap between using the last of the maincrop onions from store, and the new season's crop. 'Radar' is one of the best varieties, which produces large bulbs from late May and keeps well for several months.

Plant sets in early April and the maincrop onions should be ready to harvest by the end of August. I've scarcely ever been troubled by pests, although I find it important to cover newly planted sets with netting for a few weeks to stop cats from digging around them, or birds from pulling them up.

If taller crops, lush growth, or a lot of weeds surround the sets, you may get a build-up of stagnant air and an attack of downy mildew in a wet summer.

Onion sets like a well-prepared site with soil raked to a crumbly tilth, fertile ground and good drainage. I like to work about 60g (2oz) of fish, blood and bone meal in before the final raking. Do not grow them on the same piece of land more than once in three years.

There's no need to make a drill before planting – simply push each set into the ground so the top is almost hidden at 8-10cm (3-4in) apart in rows 25-30cm (10-12in) apart, using a wider spacing if you want exhibition-size bulbs. They need little aftercare, apart from keeping the plants weed-free and watering in a dry summer.

Sowing direct into the open garden invariably means a late harvest, so it's best to sow seed in the warm in midwinter, prick the seedlings out into modules and grow on in a greenhouse or polytunnel to transplant in mid-spring.

You can plant these daffodil-sized bulbs anytime between Christmas and Easter on almost any kind of soil. They divide into a cluster of bulbs as they develop, ripen soon after midsummer, and provide bigger bulbs for recipes that need only a small amount of onion, smaller ones for slicing raw in salads – and even smaller ones for pickling in spiced vinegar.

Save some of the best bulbs – around 2.5cm (1in) in diameter – for next year's planting and you may never need to buy new stock again.

'Golden Gourmet' and 'Pikant' are both excellent Award of Garden Merit (AGM) varieties, as is the French shallot 'Jermor' with longer roots and pink-tinged flesh.

Some varieties produce clusters with far fewer bulbs than others, in particular the show-bench favourite 'Hative de Niort'. These flagon-shaped shallots are also good for eating, but expensive to buy.

There has been a trend towards growing shallots from seed recently, which will each produce one bulb, although some may divide late in the season. Seed varieties include 'Ambition' (also available as small plants) and F1 'Matador'. Suttons has a new shallot onion called 'Zebrune' that grows from seed easily, is fast-growing and produces good crops of tasty shallots with a subtle pink tinge to the skin, says the company. This sounds great, but I shall stick with growing from bulbs that save both labour and time.

Harvest onions for storing when the foliage has died down naturally

Lift with a fork, and then dry off for 10-14 days before storing. A gently sloping shed roof can prove a good place for this, or a wire netting frame supported at the corners by stakes so water can run off and air circulate. I've also spread the bulbs out to dry on empty staging in the polytunnel during a showery summer.

Make onions into bunches or ropes once you have dried and sorted them, putting any damaged ones aside for early use. Place smaller bulbs and shallots in net bags and hang in a cool, but frost-free, outbuilding where they should store right through to late spring next year.

Sow in April in a shallow drill on soil that was manured for a previous crop and has been raked down to a good tilth. Harvest the marble-sized roots at end of summer. You can use the thinnings as salad onions.

Sow bunching/salad onions in succession from March to July. Then sow a frost-resistant variety in September that will come through the cold months for early use the following spring. 'White Lisbon' and 'Winter Hardy White Lisbon' are popular varieties, but there's now a wider choice that includes RHS AGM winners 'Feast', 'Guardsman' and the non-bulbing 'Ishikura' for sowing from March to July, and 'Ramrod' for sowing in September.

Sow seed, not too thickly, in shallow drills on good, clean soil. Keep watering and weeding, and pull as needed.

The surreal-looking Egyptian onion, or tree onion, is gaining in popularity

You plant little bulblets, or clusters of bulblets, in early autumn in a sunny spot on a good, well-drained soil. They will send up stems up to 1m (3ft) high and produce clusters of bulblets on the top the following year.

You will probably have to buy it as a pot-grown young plant growing from a single bulb, however. These are available in autumn or spring. Grow near a trellis, or stake the stems, to prevent them flopping over as they become top-heavy. If allowed to do this, they'll root as they ripen and form an onion jungle. You can eat the little bulblets in salads, pickled or cooked.

* For more on growing onions, including a panel of which types and varieties to grow and when, see the March 2008 issue of Gardens Monthly magazine, on sale 21 February.