Onion family
Onion
Allium cepa
Timings for your region
Suggested: Moderate · Explained in the glossary
Sow outdoorsearly March – mid April
Plantingmid March – late April
Harvestmid July – early September
Practical tip
Sets are the easy route; seed-grown onions store longer. Stop watering from July so the skins can dry off.
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.
All timings are guide values for the given climate, not a guarantee. Weather, aspect and variety all have a say.