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Onion

Plant sets in autumn and you have a year of kitchen onions from a bed the size of a doormat.

1. Choose sets over seed for your first year. They are small immature bulbs and are far easier.
2. Pick the right day length type for your latitude. Southern Europe wants short or intermediate day varieties.
3. Firm the bed well with your heel, then rake level. Onions hate loose fluffy soil.
4. Push the sets in so only the tip shows, 10 to 15 cm apart, rows 25 to 30 cm.
5. Net the bed for two weeks. Birds pull newly planted sets out by the dry tip.
6. Keep the rows scrupulously weed free all season, hoeing shallowly so you do not damage the roots.
7. When half the tops have bent over on their own, stop watering and let them ripen for two weeks.
8. Lift on a dry day and dry the bulbs in the sun or in an airy shed for two to three weeks.

Soil

Firm, free-draining, fertile soil at pH 6.5 to 7. Add compost the autumn before planting rather than at planting time.

Sun

Full sun. Onions size up on day length and light, so shade means small bulbs.

Water

About 15 litres per square metre per week in dry spells, then stop watering entirely once the bulbs swell and the tops start to flop.

Spacing

10 to 15 cm apart, rows 25 to 30 cm apart

Depth

Sets with the tip just showing, seed 1 to 2 cm deep

Care

['Weed weekly. Onions have shallow sparse roots and lose to weeds more than any other crop here.', 'Feed only in the first half of the season with a balanced feed, and stop by midsummer.', 'Pull off any plant that throws a flower stalk and use it first, because it will not store.', 'Do not bend the tops over by hand. Let them fall naturally or the necks bruise and rot in store.', 'In autumn-planted beds, replant any sets that frost has lifted out of the ground.']

Harvesting

Wait until around three quarters of the tops have collapsed. Ease the bulbs up with a fork and leave them on the surface for a few sunny days, roots upward. If rain is forecast move them to a dry airy place on racks or a pallet.

Storing

Dry until the necks are papery and rustle, which takes two to three weeks. Trim roots, plait them or net them, and hang in a cool dry place at 0 to 5 C with good airflow. Good keepers last six to eight months. Thick-necked bulbs never store, so eat those first.

Grow it next to

Good with carrots, beetroot, lettuce, strawberries and brassicas. Keep away from peas and beans, which do badly next to alliums.

Problems

[{'cause': 'Downy mildew, encouraged by crowding and still humid air', 'fix': 'Space wider, weed to improve airflow, and remove affected leaves. Do not grow alliums on the same ground for three years.', 'symptom': 'Yellowing leaves from the tip down with white fluffy growth underneath in damp weather'}, {'cause': 'White rot, a soil fungus that survives fifteen years or more', 'fix': 'There is no cure. Lift and bin every affected plant with its soil, and never grow any allium on that ground again. Use fresh compost in containers instead.', 'symptom': 'Plants wilt and pull out easily, with white fluffy mould and tiny black dots on the base'}, {'cause': 'Bolting, triggered by a cold spell after planting or by oversized sets', 'fix': 'Use sets under 2 cm across, plant heat-treated sets, and avoid planting into cold waterlogged soil. Eat bolted bulbs fresh.', 'symptom': 'A flower stalk shoots up in spring and the bulb goes hard in the middle'}, {'cause': 'Weed competition, wrong day length variety, or overcrowding', 'fix': 'Thin to the full 10 to 15 cm, weed weekly, and buy a variety bred for your latitude.', 'symptom': 'Bulbs stay tiny however long you leave them'}, {'cause': 'Lifted too soon, dried too little, or too much late nitrogen', 'fix': 'Stop feeding by midsummer, dry until the necks rustle, and store only hard bulbs with tight necks.', 'symptom': 'Bulbs rot in store from the neck down'}]

Saving your own seed

Onions are biennial, so you must replant a stored bulb in spring and wait for the seed head. They cross with other onions within a kilometre. Seed only stays viable one to two years, so sow it fresh.

Containers

Workable but not generous. Use a 25 cm deep trough, sets 10 cm apart, and expect medium bulbs. Spring onions and salad onions are the better container choice.