Seed Viability Checker

How long do seeds last?

Seeds are alive, but they are not immortal. From the day they are harvested, their germination rate declines — slowly at first, then faster — and the speed of that decline depends on the crop and on how they are stored. Some seeds, such as lettuce, cucumber and tomato, stay viable for five or six years in good conditions. Others, such as onions, parsnips and parsley, fade within one to three years. This checker gives you the typical storage life for each crop in our database, and a verdict for seed of the age you enter, so you can decide whether that old packet is worth sowing or whether fresh seed is the safer bet.

Storage matters more than age

The numbers here assume cool, dry storage — a sealed jar or packet in a cool cupboard, ideally with a sachet of silica gel. Heat and damp are what kill seed: a packet left in a hot greenhouse or a damp shed can lose viability in a single summer, while the same seed in a fridge can last years beyond its typical life. The enemies, in order, are moisture, heat and fluctuating temperature. A freezer is excellent for long-term storage if the seed is properly dry and sealed, but seed taken in and out of a freezer collects condensation, which is worse than steady cool storage. Whatever you do, keep seed dry first and cool second — dryness matters more than cold.

The germination test

Age and storage tell you what to expect; a germination test tells you what is actually true, and it costs nothing. Take ten seeds from the packet, space them on a damp piece of kitchen paper, fold it, put it in a sealed plastic bag, and keep it warm — on top of a fridge, or near a radiator. Check daily and keep the paper damp. After 7–14 days (longer for slow crops such as parsnips and parsley), count how many have sprouted. Eight or more out of ten means the seed is fine — sow normally. Six or seven means sow a quarter more seed than usual. Four or five means sow twice as thick, and use it only where a thin stand would not matter. Fewer than four means the seed is spent: compost it and buy fresh. The test works for almost any seed, and it is the difference between a row that comes up evenly and a row full of gaps you only discover three weeks later.

Using old seed well

Old seed is not useless seed — it just needs more of it sown and lower expectations. Sow old seed more thickly, in soil that is warm and damp, and thin to the final spacing once seedlings are up. Do not use old seed for a crop that matters to you this year — the main tomato crop, or the only sowing of a short-season vegetable — because a failed germination costs you the whole season. Use it for a second sowing, a catch crop, or a bed you can afford to re-sow. And when you buy fresh seed, write the year on the packet and store it properly from day one: the best viability checker is a packet that was never abused. Finally, remember that viability is not the same as vigour — old seed that germinates often produces weaker seedlings, so even a passing test deserves a little extra care in the first weeks.

Related tools: the Germination Time Calculator shows how long fresh seed takes to sprout, the Seed Spacing Calculator works out how many seeds you need, and the Seed-Starting Calculator gives you sowing dates. For planting dates by zone, see the planting calendar hub.