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Garden Planning, Succession & Crop RotationSeed Viability Testing Calendar
A germination test costs a few seeds and a little time, and it tells you whether an old packet is worth sowing. Do it in winter, well ahead of your sowing dates, so you still have time to reorder.
Key points
- Test old and badly stored seed in winter, before sowing or ordering.
- Use the same count each time and keep the towel damp, not soaked.
- Compare your result with the packet rate before deciding to sow, sow thicker or replace.
- Look up each crop's storage life from a university or USDA source.
- Follow the label on any treated seed.
What is seed viability and why test it?
Viability is the share of seeds in a packet that are alive and able to sprout. It drops as seed ages, and storage conditions speed or slow that drop. A packet that looks fine can still perform poorly.
Testing tells you whether to sow normally, sow thicker to make up for weak seed, or buy fresh. It is cheaper than losing a bed to a poor stand.
Viability is different from vigor. A seed may sprout in a warm paper towel yet grow weakly in cold garden soil, so a good test result does not guarantee a strong stand in a poor seedbed.
When should you test seed?
Test in the quiet part of the year, a few weeks before you start sowing or ordering. That gives you time to wait for results and still replace what fails. Test the oldest packets first, and any seed that was stored somewhere warm or damp.
Seed started indoors needs its result before the sowing date, so work backward from your planting plan. Local frost dates, from the National Weather Service or your extension office, set that plan. If you save seed from your own garden, label it clearly at harvest and test it the following winter before you count on it.
How do you run a paper towel germination test?
Count out a fixed number of seeds, such as ten, so the math is easy. Place them on a damp paper towel, fold it over, slide it into a plastic bag or container that keeps moisture in, and label it with the crop and variety. Keep it somewhere warm and out of direct sun.
Check every few days and keep the towel damp but not dripping. Different crops need different amounts of time and warmth to sprout, so look up the right conditions for each crop in your extension guide. Keep the test away from heaters and drafts, since swings in warmth and moisture can give a misleading result.
- Use the same number of seeds each time.
- Label every bag with crop, variety and start date.
- Keep the towel evenly damp.
- Count sprouted seeds when your guide says the test is done.
How do you read the results?
Divide the seeds that sprouted by the seeds you started, then compare the result with the germination rate printed on the packet. If the two are close, sow as planned. If your result is clearly lower, you have a decision to make.
For a modest drop, many gardeners sow a little thicker and thin later. For a large drop, or for expensive or hard-to-replace seed, buying fresh is often the better choice. Check your extension guidance for how to adjust seeding.
Write down the date, the count and the conditions, so that a later test of the same packet is comparable.
Which seed is worth saving or discarding?
Some crops stay viable for several seasons and others lose vigor quickly. Instead of trusting a rule of thumb from memory, look up the expected storage life for each crop from a land-grant university or USDA source.
Seed you saved from your own plants deserves a test too, especially if it came from a hybrid, since saved seed from a hybrid may not match the parent.
When in doubt about seed that has only a few seasons on it, a quick test is cheap and settles the question.
How do you plan a testing day?
Pick a quiet day in winter and test every packet you are unsure about in one batch. Set up all the bags at once, label them clearly and write the start date on a calendar so you remember when to check each one.
Record the results on your inventory sheet beside each packet. Over a few years you will learn which of your crops hold up well in your storage conditions and which need replacing every year.
What about treated seed and hygiene?
Some commercial seed is treated with a protective coating. Handle it exactly as the label directs, keep it away from pets and children, and do not mix it with food seed. Dispose of leftovers as the label instructs.
Use clean towels and containers for tests, and wash hands afterward. Discard any seed that molds during the test instead of replanting it.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.