How to Test If Old Seeds Are Still Good
Before you bin an old packet or sow it and hope, test ten seeds on damp paper. A week later you will know exactly what you are dealing with.
Quick answer
Sprout 10 seeds on damp paper, then count
- Test
- About 10 seeds on damp (not wet) kitchen paper, in a sealed bag or tub.
- Wait
- Check every couple of days; most results show within 7–14 days.
- Work it out
- Germination % = (seeds sprouted ÷ seeds tested) × 100.
- Decide
- 80%+ sow normally; 50–80% sow thicker; under 50% sow thickly or replace.
How to run the test
- Count out about 10 seeds. More (20–25) gives a steadier figure if the seed is valuable.
- Dampen kitchen paper so it is moist but not dripping; squeeze out excess water.
- Space the seeds on the paper so they do not touch, then fold it over them.
- Put it in a sealed bag or small tub and keep it warm — a kitchen cupboard is fine, but no direct sun.
- Check every couple of days. Count a seed as germinated once a root or shoot appears.
Most vegetable seed shows a result within a week to a fortnight. Very fresh or dormant seed, and slow crops like parsnip, can take longer — give them a few extra days before calling it.
Reading the result
Divide the number that sprouted by the number you tested. Ten seeds, seven sprouts, is 70%. You can do this by hand or with the germination rate calculator.
- 80–100%: healthy seed — sow exactly as you normally would.
- 50–80%: still worth using; sow a bit thicker than usual.
- Under 50%: sow thickly and expect gaps, or buy fresh for anything important.
- None: the batch is dead. Replace it.
A 10-seed test is a guide, not a guarantee
Small samples are rough. Treat the percentage as a rough signal — enough to decide whether to sow thickly or replace — not a precise measurement.
What to do with the number
The test changes how you sow, not just whether you sow. If germination is 60%, sow roughly half again as many seeds as usual to get the same number of plants. If it is 95%, you can sow sparingly.
It also tells you something about storage. If a batch that should keep for years has slumped early, the culprit is usually warmth or moisture — fix that before saving the next lot, and check how long seeds last for context.
Seeds that take their time
Some crops are simply slow, and a short test can look like a failure when it is not. Parsnip, parsley, celery and some herbs can take three weeks or more, especially in a cool room. Before you bin a batch, give slow germinators an extra week and keep them warm.
Hard-coated seed — sweet peas, some beans — benefits from soaking or nicking the coat before sowing, though that is a sowing technique rather than a test one.
Testing without kitchen paper
Damp kitchen paper is the easiest method, but not the only one. You can also:
- Sow a pinch in a pot of compost and count what comes up — closer to real sowing conditions.
- Float-test larger seeds such as beans: seeds that sink are usually viable, floaters are often empty. It is a rough check, not a germination rate.
- Test part of the packet and keep the rest back, so a failed batch does not waste everything.
How many seeds to sow after a low result
The percentage is not just information — it changes your sowing rate. If a batch germinates at about 50%, you need roughly twice as many seeds to get the same number of plants, so sow the row more thickly and thin the seedlings later. At 80% or above, sow as you normally would.
Worked example: to end up with 10 plants from a batch that tests at 50%, sow around 20 seeds. From a batch testing at 90%, about 11–12 is plenty.
Why some seeds are slow or dormant
Not all seed is ready to grow the moment it is sown. Some species have a built-in dormancy that stops them germinating until conditions are right — a cold spell, a period of warmth, or light. Parsnip, parsley and many hardy perennials can take several weeks, and hard-coated seed such as sweet peas benefits from soaking or nicking the coat before sowing. A short test on slow crops is therefore easy to misread: what looks like failure after ten days may simply be impatience.
What to do with the seed afterwards
Once you have your number, put the batch back somewhere cool and dry — the test itself does not help the seed. Two simple rules:
- Label the packet with the crop, the year and the germination rate, so future-you knows whether to sow thickly.
- Sow a little thicker for any batch below about 80%, and expect to thin the seedlings later.
Sprouted test seeds do not have to be wasted: pot them on carefully and you have a small head start, though the roots are easily damaged.
Frequently asked questions
How long does the paper test take?
Usually a week to two weeks, depending on the crop and warmth. Check every couple of days rather than leaving it.
Can I plant the sprouted seeds afterwards?
Yes — carefully lift them and pot them on. It is a genuine head start, though the roots are fragile.
Why do only some of my seeds sprout?
Age, storage heat and moisture are the usual causes. Fresh seed from a good source should sprout strongly; older seed thins out with time.
Tools for this guide
Related guides
Sources and research notes
This guide describes a standard home germination test. Results vary with crop, seed age and temperature.
Written and edited by the Seedledge Editorial. Every guide answers one real growing question, is checked against the sources listed above, and is updated when guidance changes. We are an independent editorial desk, not horticultural professionals — read how we research and update our guides.
