Garden · Seed starting
Seed viability (rag-doll test) calculator
Before you plant a whole tray with leftover seed from a couple seasons back, it's worth knowing whether it's still worth planting at all. The rag-doll test, rolling a sample of seeds into a damp paper towel and checking for sprouts, is the standard low-cost way to test viability at home. The part most guides skip is when to actually check: different seeds sprout on very different schedules, so checking too early undercounts a slow starter and checking too late risks rot. This calculator gives you both dates for your seed type.
Check schedule
5–10 days
Count any seed that's sprouted a visible root by the final count date, divide by total seeds tested, and that's your germination rate. Keep the paper towel damp, not wet, the whole time.
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How this is calculated
The rag-doll method itself comes from UF/IFAS EDIS AG182: soak seeds briefly, roll them inside a damp (not soaked) paper towel, seal loosely in a bag to hold humidity, and keep at room temperature. The seeds that sprout are viable, the ones that don't most likely won't germinate in the field either.
Timing isn't one-size-fits-all, though, since different vegetable families germinate at very different speeds. This calculator groups common seeds into three bands based on typical germination speed: fast (beans, peas, radish, and the squash/cucumber family, often sprouting within days), medium (tomato, pepper, lettuce, and brassicas), and slow (carrot, parsley, onion, leek, and spinach, all known for taking longer and germinating less evenly). This grouping is our own reasonable categorization based on general germination-speed differences between these families, not a single published table, so treat the exact day count as a planning window rather than a hard cutoff.
The "first check" date is when it's worth peeking, some fast germinators will already show roots. The "final count" date is when you tally the total and calculate a germination rate. Seeds that haven't sprouted by then are counted as non-viable.
Frequently asked questions
What counts as "germinated" for the count?
A visible root (radicle) emerging from the seed coat, even a few millimeters, counts as germinated. A swollen or split seed coat with no visible root yet doesn't count, give it until the final count date before ruling it out.
My seeds are moldy before the final count date, what happened?
The paper towel was probably too wet rather than damp, or the bag was sealed too tightly with no airflow at all. Mold doesn't necessarily mean the seeds were bad, it means the test environment was too wet, try again with a lightly damp towel and a bag that isn't fully airtight.
What germination rate means I should buy new seed?
Most home gardeners treat anything under 50% as marginal, worth using but sowing more thickly to compensate, and anything under 25% as generally not worth the growing space. There's no official cutoff, since it depends on how much seed you have and how much space you're willing to dedicate to a lower success rate.
Does this work for seeds I'm not sure of the species for?
Pick the closest match by family if you're unsure, the three bands here are broad enough to cover most common vegetable seeds. If a seed sprouts well before the first-check date or shows nothing well past the final count, that's useful information on its own about which band it actually belongs in.