Onion

Origin & history

The kitchen onion comes from Central Asia, and its wild form remains unknown to this day — it exists only in cultivation. In Egypt it was a staple food, and around 800 Charlemagne explicitly ordered it grown on the crown estates in the Capitulare de villis; it has been a garden vegetable in Central Europe ever since. That it forms a bulb at all depends on day length: only once the days are long enough does the plant lay down its leaf bases as a store.

Varieties

Yellow storing varieties such as “Stuttgarter Riesen” keep longest, red ones are milder and store less well, white ones are the shortest-lived. When buying sets, watch the size: bulbs of 1 to 2 cm across bolt far less often than fat ones, because large sets frequently already carry a flower initial inside. Heat-treated stock sold as bolt-resistant is worth the extra if your springs often stay cold for a long time.

Care

Onions have only shallow, sparse roots and lose every contest with weeds — regular shallow hoeing between the rows is the real work of the season. Water evenly until the end of June; feed only early and never with fresh manure, because late nitrogen produces thick necks that will not dry down. If a plant does throw a flower stalk, break it out at once and use that onion first — it will never store. The old practice of bending the tops over achieves nothing; the foliage goes down by itself when the bulb is ripe.

What can go wrong

The onion fly lays its eggs at the neck of young plants; the larvae eat into the bulb, the foliage yellows and the plant pulls out with no resistance. Fleece or fine netting from planting time until early June prevents this reliably, and a decent distance from last year’s onion bed helps too. Downy mildew shows up after wet weeks as grey to violet coatings on the leaves: plant further apart, water in the morning and only at the base, remove affected leaves and run the rows in line with the prevailing wind.

Harvest, storage & kitchen

Harvest once the foliage has yellowed and fallen over and the neck has gone soft — lift on a dry day and cure somewhere airy for two to three weeks, until the outer skin rustles. Only then trim the tops to a few centimetres or plait them. Store dry, airy, dark and cool but frost-free; onions with thick green necks or damage do not go into store, they go into the kitchen first.

Frequently asked questions

When and how deep do you plant onion sets?

From mid-March to the end of April, about 2 cm deep with the tip just showing above the soil, 10 cm apart in the row and 25 cm between rows. Set too deep they ripen off poorly; set too shallow and birds pull them straight back out.

Why is my onion running to flower?

A cold trigger: once the plant is established, several weeks below roughly 10 °C will set a flower bud. Such an onion is still perfectly edible — cut out the woody core in the middle and the rings around it are fine.

Are onions winter hardy?

Yes, the growing plant takes frost, and late frosts after a March planting do it no harm. Even so, wait for soil that has dried out and warmed a little: a long cold spell straight after planting pushes many onions into flower later on. Harvested bulbs, by contrast, do not tolerate frost.

Can onions be frozen?

Yes — peel, dice and freeze them raw in portions; they keep for several months and go from freezer to pan without thawing. They turn limp once thawed, so they are no longer any use raw in a salad or as onion rings.