When to sow spring onions

Start in March, as soon as the soil can be worked, and keep sowing until July. A short row every two to three weeks gives you a steady supply instead of one glut.

For spring onions in early spring, sow a winter-hardy variety in August or September. The young plants stand through winter and are ready well before the first spring sowing.

The seed comes up in one to three weeks, fastest at 59–68°F and slowly in cold soil, so don't worry if the first March sowing takes its time.

Sow thinly in drills 0.2–0.4 in deep, with rows about 8 in apart. Spring onions don't need to form a proper bulb, so they can stand close: thin them to 1–2 in apart, or sow thinly enough that you barely need to. A 120 × 80 cm raised bed fits four rows, roughly 100 to 160 onions.

They also grow well in pots at least 12 in wide, which makes them handy near the kitchen door.

Keep the rows weeded, because the thin seedlings are easily smothered, and water in dry spells so the stems stay tender.

Spring onions are usually ready about eight to twelve weeks after sowing, when they are around 6–8 in tall and the base is no more than 0.4–1 in across.

Loosen them with a hand fork if the soil is firm, then pull. Start with the biggest and leave the rest a little longer.

Two different plants are sold as spring onions. Some are varieties of the ordinary onion, Allium cepa, bred to be pulled young; they often form a small round white bulb. Others are the Welsh onion, Allium fistulosum, which stays straight like a mini leek and never forms a real bulb. German seed packets usually call these Lauchzwiebeln.

Some Welsh onion varieties, known in German as Winterheckzwiebel, are perennial. Instead of pulling the whole plant you cut the leaves, and the clump sprouts again every spring. Split and replant the clump every few years to keep it vigorous. Both kinds grow the same way from seed.

Onion fly is the main pest: its maggots eat into the base of young plants, which yellow and collapse. Cover the rows with fine insect mesh straight after sowing.

In wet weather downy mildew can cover the leaves with pale patches and a grey-violet fuzz. Sow thinly so air moves between the plants, and don't sow onions on the same spot year after year.

Spring onions belong to the onion family and share its diseases, including white rot. Treat them as part of the onion group in your rotation and never sow them where white rot has appeared.

Because they are small and quick, spring onions are easy to tuck between slower crops such as carrots or lettuce. Claims that they keep pests off their neighbours are tradition with little evidence behind them.

As with all alliums, avoid sowing them right next to or straight after other onion-family crops, which share their pests and diseases.