Seed Viability & What's Left After Storage

Seed viability decay is the gradual loss of germination capacity as seed ages in storage. Living seed slowly uses up its reserves and accumulates damage, so a lot that germinated 95% fresh may germinate far less after a few years. How fast it falls depends on the species and on how cool and dry the seed is kept.

Viability = initial germination × (1 − annual decline)^years. Each year the lot keeps the surviving fraction of the previous year's viability, so the loss compounds. For example 90% germination declining 10% a year is 90 × 0.9² ≈ 73% after two years, and about 59% after four — the curve falls faster the longer it is stored.

Mainly species, seed moisture and storage temperature. Oily seeds and short-lived species (onion, leek, parsnip, soybean) decline fast; cereals and many legumes last longer; tomato and many brassicas are very long-lived. Cool, dry storage slows decline sharply — the classic rule is that each drop in temperature and moisture roughly extends seed life.

Below about 70% germination most seed lots need attention — either raise the seed rate to compensate for the dead seed, or replace the lot. Certified-seed standards for many crops sit around 70–85% minimum germination. Very low viability also tends to give weak, uneven seedlings, not just fewer of them.

Divide your target plant population by the viability fraction (and by emergence/field-establishment losses). If you need a stand that 80% viable seed would give but your lot is only 60% viable, you sow roughly 80 ÷ 60 ≈ 1.33 times as much seed. The Seed Rate calculator does this adjustment for you.

Keep seed cool and dry — low moisture content and low temperature are the two big levers. Dry seed well before storage, use sealed containers with a desiccant for long-term keeping, and store away from heat and humidity. The drier and cooler the store, the slower viability falls.

A germination test is the gold standard — it tells you the actual current germination of your lot rather than a model estimate. Use this decay calculator to anticipate roughly where a lot stands and whether it is worth testing, then run a quick rag-doll or tray germination test before committing the seed to the field.

Yes. Vigour usually declines before germination percentage does, so an aging lot may still germinate reasonably in a lab test but emerge slowly and unevenly in cold or crusted soil. Treat a marginal lot cautiously: even if the germination number looks acceptable, expect weaker field performance.

They're a planning model. Real decay isn't perfectly constant year to year, and storage conditions vary, so the true viability of a specific lot can differ. Use the estimate to decide whether to test or replace seed, and confirm with an actual germination test before sowing.