Why Are My Leek Seeds Not Germinating?

Leek seeds can be maddeningly slow and uneven to germinate compared to many other vegetables. Sow a tray in January or February and you may wait four weeks with little to show for it, then find germination picking up rapidly as temperatures rise. Understanding the specific conditions leek seeds need helps you diagnose a failure and improve germination rates for future sowings.

Temperature is the primary trigger

Leek seeds require a soil temperature of at least 7°C to germinate, with optimal rates occurring between 15°C and 25°C. Below 10°C, germination slows dramatically — seeds may take four to six weeks to emerge rather than the standard ten to fourteen days at ideal temperatures. Many home growers sow leeks in January or early February on windowsills or in unheated greenhouses where temperatures fluctuate widely. If your sowing medium is cold overnight, even if warm during the day, germination will be very slow. A heated propagator maintaining a steady 18–20°C transforms leek germination — seeds will emerge in ten to fourteen days reliably.

Old or poorly stored seed

Leek seed has a relatively short viable life compared to some vegetables — typically two to three years under ideal storage conditions. Seeds stored in a warm, humid kitchen lose viability faster. If you are using seed more than two years old, germination rates will be noticeably reduced even under good conditions. Always check the pack date and do a simple germination test (place ten seeds on moist kitchen paper in a warm spot; count how many germinate in fourteen days) if you have any doubt about seed quality before committing a full tray.

Sowing too deep

Leek seeds are small and should be sown at a depth of no more than 5–10 mm. Seeds sown too deeply (more than 1 cm) run out of energy before the seedling can reach the surface. In a seed tray, lightly press the surface flat, scatter seeds thinly, then cover with a fine layer of vermiculite or sifted compost no deeper than the seed itself. Water with a fine rose to avoid washing seeds deeper into the compost.

Drying out between waterings

Germinating seeds that dry out completely between waterings die before emerging. The sowing medium must be kept consistently moist — not waterlogged, but never allowed to dry out. Covering the tray with a clear lid or propagator dome helps maintain moisture and warmth. Check daily and water from below (stand the tray in water briefly) to avoid disturbing the seed surface.