Gadenin日本語Get the appWhy leeks are started early
Leeks are slow. From seed to a usable stem takes most of a growing season, and the thick white shank that makes a leek worth growing only develops once the plant has had months to bulk up. That is why most home gardeners start them under cover in late winter or early spring, well before the soil outside is warm enough, and plant them out once the seedlings are sturdy.
In mild-winter areas you can also sow in an outdoor seedbed in spring and transplant from there in early summer. The plants end up a little smaller, but the method needs no indoor space at all. Where summers are hot, the timing flips: leeks are grown through the cool half of the year, sown in late summer and harvested over winter and early spring.
| Climate | When to sow | Where |
|---|---|---|
| Cold winters, warm summers | Late winter to early spring | Indoors or in a cold frame, under lights if needed |
| Mild winters, cool summers | Late winter to mid spring | Indoors, a cold frame, or an outdoor seedbed in spring |
| Hot summers, mild winters | Late summer to early autumn | Trays in a shaded spot, then out as the heat breaks |
Leek seed is short lived compared with many vegetable seeds. Old packets often germinate poorly, so buy fresh seed or test a pinch on damp paper first.
Sowing the seed
Leek seed germinates best in moderate warmth, roughly 60 to 70°F (15 to 21°C). It will still come up in cooler conditions, just slowly and unevenly. A heated propagator is not necessary; a bright windowsill or a cool greenhouse is usually enough. Once the seedlings are up, cooler growing conditions and plenty of light keep them stocky instead of thin and floppy.
Most gardeners sow in a deep tray or in modules. Seedlings in a tray are separated and planted bare-root later, which is how leeks have always been grown. Modules let you sow a small pinch per cell and plant the clump out as one, an approach some growers use for slightly smaller but uniform leeks.
- Fill a deep tray or modules Use a fine, free-draining seed mix and water it before sowing so the seed is not washed around. Leeks root deeply, so a tray at least 3 inches (7.5 cm) deep is better than a shallow seed tray.
- Sow thinly and cover lightly Scatter the seed thinly or sow in short rows, then cover it with about 1/4 inch (6 mm) of mix. The seedlings come up as thin folded loops before straightening, which is normal.
- Keep evenly moist and bright Never let the tray dry out completely during germination. Once the seedlings are up, move them to the brightest spot you have and keep them on the cool side.
- Trim the tops if they flop If the leaves grow long and fall over, cutting them back by about a third with clean scissors keeps the seedlings upright and encourages thicker stems. Many growers do this two or three times before planting out.
Sowing in an outdoor seedbed
Where spring is reasonably mild, leeks can be sown outdoors in a nursery bed instead of indoors. Choose a sheltered, sunny patch with fine, weed-free soil, and wait until the soil has warmed enough to work comfortably. The seedlings stay there until they reach planting size and are then lifted and moved to their final bed, so a small seedbed can raise enough plants for a large row.
- Prepare a fine seedbed Rake the soil to a fine crumb and remove stones and weeds. Water the bed the day before sowing if it is dry.
- Sow in shallow drills Make drills about 1/2 inch (1 cm) deep and about 6 inches (15 cm) apart, sow thinly along them, and cover lightly.
- Thin and weed Thin crowded seedlings so each has a little room, and keep the bed weeded; young leeks are easily swamped.
Birds and slugs both find young leek seedlings. A cover of fine mesh or row cover over the seedbed protects them until they toughen up.
Growing on to planting size
The aim of the seedling stage is a sturdy plant with a stem roughly as thick as a pencil and about 8 inches (20 cm) tall, which usually takes a couple of months or more from sowing. Light and cool temperatures do most of the work. Seedlings kept too warm or too dark stretch into thin, floppy plants that struggle after transplanting.
Feed lightly once the seedlings have been growing for a few weeks, especially in trays where the mix runs out of nutrients. A dilute liquid fertilizer every week or two is enough. Planting out itself, including trimming and setting the seedlings, is covered in the planting guide.
- Keep them cool and bright Once up, grow the seedlings in the brightest, coolest place available, such as a cold frame or an unheated greenhouse, rather than a warm room.
- Feed lightly Give a weak liquid feed every week or two after the first few weeks to keep the seedlings green and growing.
- Harden off About a week before planting out, set the seedlings outside for longer each day so they adjust to sun, wind and cooler nights.