How long seed lasts, and how to store it

Seed packets carry a sow-by date and almost never an explanation. The honest version is that most vegetable seed stays useful for years, a few crops are worth replacing annually, and the difference between the two is almost entirely about moisture.

How long seed lasts, by crop

These are working figures for dry seed kept cool and dry — which a kitchen cupboard is not, and a shed definitely is not. They describe how long germination stays useful, not the day it stops.

The pattern is worth seeing plainly: alliums at one to two years while cucumber runs to ten. Onion and leek seed is the one packet genuinely worth buying fresh every season, and no storage trick rescues it.

Why seed dies: moisture first, heat second

Seed is alive and slowly respiring. Two things kill it. Moisture drives the respiration rate up and lets fungi in; warmth accelerates the same chemistry. A widely used rule of thumb is that each 1 per cent drop in seed moisture, or each 5 °C drop in storage temperature, roughly doubles storage life. You cannot easily measure the first, but you can control the second.

This is why a beautiful seed tin on a windowsill is the worst place in the house: warm, and cycling between humid and dry every day.

How to store seed so it actually keeps

• Dry it first. Seed should snap when bent, not bend. Freshly harvested seed that goes into a jar still damp will mould, and the whole jar goes with it.
• Silica gel in a sealed jar is the single biggest improvement most people can make. A sachet per jar, replaced when it stops being dry.
• Cool, dark, stable. A cupboard away from the kitchen is fine. A fridge is better for long-term storage, provided the jar is genuinely sealed.
• Freezer only for fully dry seed. Frozen damp seed is dead seed, and the damage shows up months later as poor germination rather than immediately.
• Label crop and year. An unlabelled jar of small brown seeds is a coin toss, and you will not remember.

How to test old seed before you rely on it

Ten seeds on damp kitchen paper in a sealed bag, somewhere warm and out of the light. Count what germinates after the crop’s usual period — see the germination times table for how long that is.

The arithmetic matters more than the raw count. Eight out of ten is 80 per cent, which means sow roughly a quarter more thickly than fresh seed. Four out of ten means buy new seed, or sow four times as thick and accept the gaps. Zero means the seed is dead however it looks.

When old seed is fine, and when it is not worth it

Old seed germinates slower and less evenly — that is the honest summary. For a home garden, three-year-old tomato seed is perfectly usable. It is not *equivalent* to fresh seed, so do not judge a variety on a poor year from an old packet.

Where it is not worth it: alliums, parsnip, and anything where the packet is already two seasons old and you are direct-sowing into a bed you have prepared. Re-sowing a gap costs more than the packet.

Common storage mistakes

• Storing in a shed or greenhouse — temperature swings and humidity.
• Keeping seed in the paper packet, open, in a drawer.
• Adding seed to a jar that still has damp seed in it.
• Freezing seed that is not fully dry.
• Assuming germination percentage is either 100 or 0 — it declines smoothly.

Frequently asked questions

Can I use seed from last year’s packet?

For most crops, yes — germination declines rather than stopping. Test ten seeds on damp paper before you commit a bed. Alliums and parsnip are the exceptions worth replacing annually.

Does freezing seed kill it?

Not if the seed is fully dry. Freezing is a good long-term method precisely because it slows respiration. Freezing seed that still holds moisture ruptures cells and kills it, which is why dry-first is the rule.

How do I know seed is dry enough to store?

It snaps when you bend it rather than flexing, and it does not clump. Large seed like beans should shatter rather than dent. When in doubt, a week in a warm dry room in an open container before it goes into the jar.

Should seed be stored in the fridge or the freezer?

The fridge is the practical choice for most people: cool, stable and easy to seal. The freezer is better for multi-year storage of fully dry seed, but the failure mode is worse, so it is not the place to experiment.

Related

• Isolation distances and seed life, by crop — the full table including isolation distances
• Germination times by crop — how long to wait before deciding a test failed
• Seed saving protocols — wet and dry processing, crop by crop
• Crop hubs — varieties by crop, with hybrid or open-pollinated flagged on every listing