When should I plant onion sets in the UK?

Mid-March to mid-April in southern England, late March to early May in the Midlands, mid-April to early May in northern England and Scotland. Earlier sowings risk bolting; later ones don't have time to make a decent bulb. Heat-treated sets resist bolting and can be planted from late March even in the south.

Why are my onions bolting (going to flower)?

Bolting (premature flowering) usually means cold weather hit the sets when they were young, signalling that they've been through a winter. Heat-treated sets resist bolting. If you find one bolting, pull it; the bulb won't store but is fine to eat fresh. Other causes: planting too early, water stress, planting larger sets (smaller sets bolt less).

Sets or seed — which is better?

Sets are easier, faster, more reliable, and what nine out of ten UK gardeners grow. Seed gives access to more cultivars (especially storage varieties like Bedfordshire Champion), often produces firmer bulbs that store longer, and avoids the bolting tendency of sets. Sow seed indoors in January to February, transplant in April. For first-year gardeners, sets are the answer.

How big do UK onions get?

Most main-crop varieties form bulbs 5–8 cm across — fist-sized. Sturon and Stuttgarter Riesen are reliable medium-sized croppers. Exhibition varieties (Kelsae, Ailsa Craig) can reach 15–20 cm with sustained feeding and watering. Smaller, dense bulbs store longer than huge fluffy ones.

When are my onions ready to harvest?

Late July to early September. Watch the foliage — when about three-quarters has yellowed and toppled, the bulbs are mature. Don't bend the necks deliberately to speed ripening; you'll wound the bulb and ruin storage life. Lift on a dry day with a fork; lay on top of the soil to dry in the sun.

How long do home-grown onions store?

Properly cured storage varieties (Bedfordshire Champion, Sturon, Red Baron) keep 6–9 months in cool dry conditions. The trick is full curing — necks must be papery and fully dry before you stack them; any green left in the neck rots downwards into the bulb. Check stored onions monthly; soft ones go to the kitchen immediately.

Zwiebel

Allium cepa

Pflanzen Sie Zwiebel-Setzlinge von Mitte März bis Mitte April in Südengland, im Norden Ende April – oder säen Sie die Samen ab Januar im Haus vor, um sie im April auszusetzen. Zwiebeln sind winterhart (RHS H5) und vertragen als Jungpflanzen Frost. Sie benötigen ein sonniges, gut durchlässiges Beet mit geringem Stickstoffgehalt; nährstoffreicher Boden führt zu üppigem Blattwuchs und zu kleinen Knollen. Pflanzen Sie die Setzzwiebeln im Abstand von 10 cm, sodass die Spitzen gerade aus dem Boden ragen. Ernten Sie von Ende Juli bis Anfang September, wenn das Laub vergilbt und umfällt. Trocknen Sie die Knollen eine Woche lang in der Sonne und lagern Sie sie anschließend an einem luftigen, frostfreien Ort; richtig getrocknete, in Großbritannien angebaute Zwiebeln halten sich bis April oder länger.

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