OnionAllium cepa

The onion wants sun from morning to evening and a soil that dries quickly after rain. Give it the best-exposed bed, away from hedges and tall vegetables that would shade its thin foliage. Avoid the bottom of the garden where water stands in winter and spring: in our loamy or clay soils, that is where the bulbs rot. Ideally, the bed received compost for the previous crop, for example squashes, potatoes or cabbages. Keep a rotation of three to four years with garlic, shallots and leeks, which share the same diseases.

Work the soil with a broadfork or a garden fork in late winter, without turning it, then crumble it finely with a rake. Above all, add no fresh manure or young compost: they rot the bulbs and attract the onion fly. In heavy soil, work in two or three buckets of coarse sand and very mature compost per square metre, or build a raised bed ten to fifteen centimetres high. Then let the soil settle for one to two weeks before planting: the onion likes a settled soil, not a fluffed-up one where the roots find no purchase.

To start with, sets are the surest route: they come up quickly, stand up to slugs and give a harvest in four months. Choose firm sets the size of a hazelnut, with no green shoot or soft patch. Large sets bolt more easily. Sowing, which is cheaper, suits storage varieties such as Jaune paille des Vertus or white onions: it needs a fine tilth, a slow germination of two to three weeks and meticulous weeding. A third option, the module-grown plants sold in garden centres in April, combines the advantages of both.

Plant summer onions as soon as the soil can be worked without sticking to your boots, generally between mid-March and mid-April in Belgium. Planting in cold, waterlogged soil rots the sets or triggers bolting. Mark out rows twenty-five centimetres apart, and push each set in point upwards every ten centimetres, until only the tip shows. Firm lightly with the flat of the hand. If blackbirds and magpies pull up the freshly planted sets, cover the bed with a net or fleece for two weeks, until the roots have anchored.

Overwintering varieties, such as Radar, Senshyu or Shakespeare, are planted between mid-October and mid-November and harvested from June, when shop onions are at their dearest. They come through our winters without protection, but absolutely demand a well-drained soil: on a raised bed or a fifteen-centimetre ridge, otherwise the winter rain rots them. Space them a little more widely, fifteen centimetres, as they grow larger. Do not mulch them; moisture at the neck is fatal to them. In spring they get away early and deliver their harvest before the heavy downy mildew attacks of July.

The onion makes do with a container at least twenty-five centimetres deep, filled with two thirds potting compost and one third sand or perlite for drainage. Plant the sets every ten centimetres, tip just showing, and place the container in full sun against a south-facing wall. Water only when the compost is dry three centimetres down. Containers suit white spring onions and Welsh onions particularly well, as these are picked young; large storage onions stay smaller in them. On a balcony, the onion fly is rare, which is a real advantage.

The first mistake is burying the sets too deep: they become drawn and the bulb stays small. The second is planting in freshly manured soil, which attracts the fly and causes rot. The third is squeezing the rows together to save space: without air, downy mildew moves in and the foliage never dries. Weeding is also often forgotten, whereas the onion, with its narrow foliage, gets smothered by chickweed in a few weeks. Finally, planting too early, in February, in cold soil, triggers bolting: better to wait a fortnight longer.

The onion is one of the most frugal vegetables in the garden. After planting, a single watering is enough to bring the sets into contact with the soil. After that, water only in marked drought, when the soil is dry five centimetres down and the foliage turns bluish, generally not before May or June in our climate. Water at the base, early in the morning, without wetting the leaves, at the rate of one watering can for two metres of row. Stop all watering as soon as the leaves begin to flop over, about a month before harvest: a bulb full of water keeps badly.

Regular hoeing is a better substitute for both watering and mulching. Run the hoe between the rows every ten to fifteen days, especially after rain, to break the crust and aerate the soil. Close to the bulbs, pull weeds by hand so as not to damage the skin. If you insist on mulching, choose a fine, dry mulch such as dried grass clippings, no more than two centimetres deep, and always keep the neck clear. No fertiliser is needed in soil properly composted the year before; too much nitrogen gives lush foliage and soft bulbs that rot in the cellar.

From June onwards, the bulbs swell and lift themselves naturally out of the soil: do not try to cover them, as this is how they ripen and how their skin colours. Even draw the soil away from them a little to expose them to the sun. If a flower stalk appears, recognisable by its thick stem and its swelling, cut it off at once level with the leaves: the bulb will still be edible but will not keep, so eat it first. Do not bend the leaves over to hasten ripening, as used to be advised: it opens a door to neck rot.

The onion fly lays its eggs in April-May at the base of the young plants; its larvae bore into the bulb, which yellows and comes loose. Lay fine insect-proof mesh from planting until mid-June, and alternate the rows with carrots, whose scent confuses the trail. Pull up and bin any wilted plant. Against downy mildew, which coats the leaves in grey felt in warm, damp weather, space the plants out, never wet the foliage and spray horsetail decoction every ten days from June until harvest. A four-year rotation remains the best protection against white rot.

In March-April, plant, lay the mesh and watch out for birds. In May, hoe every two weeks and pull weeds by hand. In June, remove the mesh, expose the bulbs, water once or twice if the month is dry and remove flower stalks. In July, stop watering, watch for downy mildew and prepare a dry space for drying. In August, harvest the summer onions, dry, sort and store. In October-November, plant overwintering onions on a raised bed, and put any remaining sets away somewhere dry so they do not sprout.

Harvest when two thirds of the leaves have flopped and yellowed, on a dry morning, lifting the bulbs with a fork without pulling on the tops. Leave them to dry on the ground, roots upwards, for three to five days of dry weather, or spread them on a slatted rack under an airy shelter if it rains. Drying continues for two to three weeks, until the neck is thin and dry and the skin rustles. Never wash onions; just brush off the soil. Careless drying is the leading cause of rot in the cellar: take your time, storage depends on it.

To never run short of onions, combine three crops: overwintering onions planted in October for a June harvest, spring sets for winter storage, and a mid-August sowing of white onions under fleece for small fresh onions from April. Storage onions kept between 5 and 15 °C in a dry, dark place last until March; check them every month and eat the largest first, as they keep less well. Bulbs that sprout in late winter can be replanted in a pot to provide green onion tops until the first harvests.