Why Won't My Lettuce Seeds Germinate?

Lettuce is usually quick and easy to germinate, so when the seeds fail to come up it is worth knowing the specific quirks that trip people up — chiefly that lettuce seed dislikes heat, wants to be sown shallow, and must not dry out. Get those right and lettuce sprouts readily. Let me walk you through what lettuce seeds need and what typically goes wrong.

Heat is the surprising enemy

Unlike warm-season crops, lettuce seed germinates best in cool conditions and can actually refuse to sprout when the soil is too warm — a behaviour called thermo-dormancy. Above roughly 25°C, and especially above 27–30°C, many lettuce varieties simply will not germinate, going dormant instead. This is the most common reason for failure in summer sowings. The fix is to sow when it is cooler, or to start seed somewhere cool — even chilling seed in the fridge for a few days before sowing, or sowing in the evening and keeping the soil cool and shaded, helps. (This is the opposite of warm-season crops, which is what catches people out.)

Sow shallow — lettuce needs light

Lettuce seed is small and needs light to germinate, so it must be sown shallow — barely covered, just a few millimetres deep, or pressed onto the surface with a fine sprinkle of soil. Sown too deep, it exhausts itself before reaching the surface, or the lack of light keeps it dormant. This is a very common mistake. Surface-sow or barely cover lettuce seed, and keep that thin surface layer consistently moist.

Moisture and drying out

Because lettuce is sown so shallow, the seed and the surface must stay consistently moist — a shallow-sown seed dries out fast, and a single dry-out can kill germinating seed. Keep the surface evenly damp with gentle watering, and cover with a board, fleece or fine mulch until germination to hold moisture (remove as soon as seedlings appear, since they need light). At the same time, avoid waterlogging, which rots seed. Even, gentle moisture on a shallow sowing is the balance to strike.

Seed quality and patience

Lettuce seed is relatively short-lived, so old seed germinates poorly — use fresh seed, ideally less than two to three years old, for good results. In cool, moist, shallow conditions lettuce germinates fast, often within a week, sometimes just a few days, so it does not need much patience — if nothing is up after a week or two, suspect heat dormancy, too-deep sowing, drying out, or old seed rather than simply needing more time. Put it together: sow fresh seed shallow (barely covered), keep it cool (under about 25°C) and consistently moist, and lettuce comes up quickly and reliably.