Gadenin日本語Get the appSow in a controlled bed, not where the plants will live
Welsh onion seedlings emerge as a single bent thread and stay thinner than a pin for weeks. Broadcast into open ground they lose to every weed that comes up beside them, and half of them get hoed out by accident. Raise them in a seed tray, a module tray or a small nursery bed you can weed on your knees, then move them once they are thick enough to see.
Modules are the easiest route because this crop transplants without complaint. Sow six to ten seeds into each cell and grow the whole cell on as one clump. Welsh onion is a bunching plant by nature, it divides at the base whether you ask it to or not, so a multi-sown clump is not a compromise, it is how the plant grows anyway. A tray of forty cells sown this way gives you more standing onion than a whole row of bulb onions.
Buy fresh seed every year. Allium seed loses viability fast, and a packet kept warm through one summer often drops from near total germination to under half without looking any different.
Temperature, depth and how long it takes
The seed wants to be barely covered, about a quarter inch (5 mm) of fine compost, then firmed so it sits against damp material. Deeper sowing does not fail outright but it delays and staggers emergence, and a staggered clump is harder to manage later because half of it is always the wrong size.
Germination runs best between 60F and 75F (15C to 24C). It still works down to 50F (10C), just slowly, and it slows again above 85F (29C). Expect the first threads in seven to fourteen days in warm conditions and up to three weeks in a cool spring. Nothing about that is a problem, but it means you should not give up and resow at day ten.
| Soil temperature | Days to emerge | What to expect |
|---|---|---|
| Below 50F (10C) | Twenty or more | Patchy and uneven, better to wait |
| 55F to 60F (13C to 15C) | Fourteen to eighteen | Slow but even |
| 65F to 75F (18C to 24C) | Seven to twelve | The reliable range |
| Above 85F (29C) | Erratic | Shade the tray and water in the morning |
Two sowing windows, and what each one gives you
Sow in early spring as soon as you can keep a tray above 55F (13C) and you will be cutting from midsummer, with a clump strong enough to stand through its first winter. Sow again in late summer, at least ten weeks before your first frost, and those plants sit small over winter and come away hard in early spring, filling the gap when nothing else is ready.
Because this is a perennial you only need to do this once seriously. After the first year you increase your stock by dividing clumps rather than by sowing, which is faster and gives you full sized plants immediately. Keep sowing seed only if you want to widen the planting or replace a bed that has gone tired.
Thinning, feeding and knowing when to move them
The single number to hold on to is eight to ten weeks from sowing to planting out. Everything before that is just keeping small seedlings alive, weeded and slightly hungry rather than lush. A tough, slightly hard grown seedling establishes far better than a soft one raised under cover and pushed with feed.
- Do not thin a multi-sown cell If you sowed six to ten seeds per module, leave every one that came up. They will lean apart on their own as they thicken. Thinning a clump you intend to plant as a clump throws away the crop.
- Thin a seed bed to a half inch In an open nursery bed, thin to about a half inch (1 cm) between seedlings once they have two leaves. Crowded seedlings in open ground stretch and flop and never recover their thickness.
- Feed weakly from the third week Give a dilute liquid feed every ten days once the second leaf shows. Seedlings raised in a small volume of compost run out of nitrogen quickly, and pale seedlings transplant badly.
- Trim the tops if they flop If the leaves get long enough to fall over, cut them back to about four inches (10 cm) with scissors. It thickens the base and makes the seedlings much easier to handle at planting.
- Move them at pencil thickness Transplant when the seedlings are six to eight inches (15 to 20 cm) tall and the base is roughly as thick as a pencil lead. That takes eight to ten weeks from sowing. Moving them earlier works but they sulk for a month.
What to write down this year
Record the sowing date, the number of seeds you put in each cell and the date the first threads appeared. Next season that gap tells you at a glance whether your bench was warm enough, and it is the only way to tell a bad batch of seed from a cold spring. Note the transplant date and the height at transplanting too.
Also note which end of the tray came up first. Trays are rarely uniform, and after one season you will know that one corner of the bench or one end of the frame runs cooler, which changes where you put the next sowing.