Wondering how to test if seeds are still good? Place 10 seeds on a damp paper towel, fold it over, seal it in a plastic bag, and keep it warm (70–80°F). Check after the days to germination printed on the packet, or in 7–10 days. The number that sprout out of 10 is your germination percentage — 8 or more means sow as normal.
Why old seeds fail — and why the packet date is not the deadline
Seeds do not expire on a fixed date. A packet loses a little germination power each year, faster when it was stored warm or damp and slower when it was stored cool, dry and dark. University of Illinois Extension recommends storing seeds below 45°F in a sealed jar or bag in the refrigerator, and gives a useful rule of thumb: the storage temperature in Fahrenheit plus the percent relative humidity should stay under 100. A packet past its “packed for” year can still be perfectly usable — and a fresh-looking packet stored on a damp garage shelf can already be dead. Only a germination test tells you the truth about the packet in your hand.
How long do seeds last? A viability chart by crop
These are typical storage lives for seed kept cool, dark and dry (Purdue University Extension, based on Knott’s Handbook for Vegetable Growers). Treat them as planning figures, not deadlines — always test before you trust them.
| Crop | Typical viable life | Notes |
|---|---|---|
| Tomato, cucumber, melon | 4–5 years | Among the longest-lived vegetable seeds |
| Lettuce | 1–6 years | Sources disagree — test, don’t guess |
| Onion, leek, parsnip | 1–2 years | Shortest-lived; test every year |
| Pepper, eggplant | 2–4 years | Warmth-loving; test before sowing |
| Beans, peas, corn | 2–3 years | Large seeds; the float test does not work reliably |
| Carrot, parsley | 2–3 years | Slow to germinate even when fresh |
| Cabbage, broccoli, kale | 4–5 years | Brassicas hold up well in storage |
| Squash, pumpkin | 4–6 years | Thick coats protect them |
The 10-seed paper towel test (step by step)
This is the method University of Illinois Extension and University of Wisconsin–Madison Extension both recommend. Ten seeds make the maths easy: each sprouted seed is 10%. It is the same approach in our guide to how to germinate seeds — the test simply measures the result instead of growing the seedling.
- Count out 10 seeds from the packet — same crop, same variety.
- Dampen a paper towel until it is moist but not dripping. Lay the seeds on one half and fold the other half over them.
- Slide the towel into a sealable plastic bag, leaving it about 70% sealed so a little air circulates, and label it with the crop and the date.
- Keep it warm, 70–80°F. The top of a refrigerator works well. Light is not needed.
- Check every 2–3 days and re-dampen the towel if it dries out. Count a seed as sprouted when a small root pokes out.
- Count after the packet’s days-to-germination, or in 7–10 days if you no longer have the packet. Slow crops like peppers and parsley can need 2–3 weeks.
Reading your result — what the percentage means
| Germination rate | What to do |
|---|---|
| 8–10 out of 10 (80–100%) | Sow as normal. The packet is in great shape. |
| 7 out of 10 (70%) | Usable — sow a little thicker than normal to fill the gaps. |
| 5–6 out of 10 (50–60%) | Tired seed. Sow about twice as thickly, or replace it if the crop matters. |
| Below 5 out of 10 (under 50%) | Buy fresh seed. Below about 40%, Wisconsin Extension advises replacing the packet — the seedlings that do emerge may be stunted and unproductive. |
Run the test about a month before sowing, so a failed packet is a shopping trip instead of a lost row. Write the result and the date on the packet — a seed box with test dates on it is a plan.
The float test does not work — skip it
Dropping seeds in water to see which sink is a popular tip, but it is not reliable. Good seeds can float because of air trapped in the seed coat, and dead seeds can sink. The paper towel test is the only home method extension services recommend.
What if seeds fail the test — is it dormancy or death?
A failed test usually means the seed is dead, not dormant. Most vegetable seeds lose their shallow dormancy in dry storage, so an old packet of lettuce or beans that fails a warm, moist test is most likely dead — soaking or scratching it will not help. Scarification and cold stratification belong to species that need them even when fresh, such as many perennials, trees and shrubs. If your seeds are fresh but still will not sprout, check the germination temperature chart — wrong soil temperature is the most common cause — and see why your seeds are not germinating.
How to store seeds so they last longer
- Keep them cool, dry and dark — a sealed jar in the refrigerator is ideal.
- Dry seed before storing; moisture is what ages seed fastest.
- Label every packet with the crop, variety and year.
- Test a few seeds from each packet every year or two, and grow out the short-lived crops (onion, parsnip, lettuce) before they fade.
Frequently Asked Questions
How can I tell if old seeds are still good?
Run a 10-seed paper towel test: 10 seeds on a damp paper towel in a sealed bag at 70–80°F, checked in 7–10 days. The number that sprout out of 10 is your germination percentage.
Do seeds expire?
Seeds do not expire on a fixed date. Germination falls a little each year, faster in warm or damp storage. Most vegetable seeds last 1–5 years when stored cool, dry and dark — a germination test tells you whether a specific packet is still worth sowing.
What germination rate is too low to plant?
Below 50% is generally not worth sowing, and below 40% extension services recommend buying fresh seed, because the seedlings that do emerge may be stunted and unproductive.
Can I just plant old seeds thicker instead of testing?
You can, but you are guessing. A 10-minute test a month before sowing tells you exactly how thick to sow — or whether to buy fresh seed before planting day.
Does the float test tell me if seeds are viable?
No. Good seeds can float and dead seeds can sink. The paper towel germination test is the reliable home method.
