QUICK ANSWER
A simple seed viability test tells you in about a week whether last year’s leftover seeds are worth planting — before you waste precious early-season weeks waiting on seeds that were never going to sprout. Fold 10 seeds into a damp paper towel, seal it in a bag, keep it warm, and count how many germinate.
Why a Seed Viability Test Is Worth the Five Minutes
Skipping a seed viability test on old seed feels like the faster option — just plant them and see. In practice, it usually costs more time than it saves. Plant a packet that’s mostly dead, and you won’t know anything’s wrong for a week or two. By the time you notice bare soil where seedlings should be, you’ve lost real weeks off an already-short growing season, and you’re now scrambling to source replacement seed and replant later than planned. A seed viability test takes about the same week of waiting, but tells you the truth up front, while there’s still time to act on it.
Seeds don’t have one fixed expiration date the way food does. Viability declines gradually, and the pace depends heavily on the type of seed and how it’s been stored. Some seeds are simply short-lived by nature — parsley and onion are two of the fastest to fade, often losing real viability inside a couple of seasons no matter how carefully you store them. Others hold on for years: cabbage and watermelon seed, for instance, can still germinate reliably well past the four-year mark under decent storage conditions. A seed packet’s printed date is a starting reference, not a hard cutoff — which is exactly why testing matters more than guessing based on age alone.
How to Run a Seed Viability Test
• Count out 10 seeds from the packet you’re unsure about — a sample size of 10 makes the math simple and gives a reasonably reliable read on the whole packet.
• Dampen a paper towel — moist throughout, but not dripping wet. Too much water can rot the seeds instead of germinating them.
• Space the seeds evenly on the towel, then fold it over so they’re covered but not crushed.
• Seal the folded towel in a plastic bag or airtight container, and label it with the variety and date so you don’t lose track of what’s testing.
• Keep it somewhere warm — around 70°F is ideal. The top of a refrigerator or a warm windowsill both work well.
• Check daily starting around day 3, and continue for up to two weeks depending on the seed type — some germinate in days, others take longer even when perfectly viable.
What Your Results Actually Mean
Once you’ve counted how many of the 10 seeds sprouted, the number translates directly into a planting decision:
• 8 to 10 sprouted — good viability. Plant this packet at the normal rate listed on the packaging.
• 5 to 7 sprouted — still usable, but sow more thickly than usual (roughly 1.5 times the normal seed count) to compensate for the lower success rate.
• Fewer than 5 sprouted — the packet isn’t worth planting as your primary seed source. If it’s a variety you specifically want, you can still try it alongside fresh seed as a backup, but don’t rely on it alone.
This same test also works as a general planning tool beyond just judging old seed — if you’re ever unsure whether a germination problem in the garden was a seed issue or a growing-conditions issue, testing a sample from the same packet indoors gives you a clean answer either way.
If you have several old packets to sort through, testing them in one batch is worth the small extra setup — label each bag clearly with the variety, since folded paper towels can look identical once sealed. Working through your whole seed box at once, rather than testing one packet at a time as spring approaches, gives you a full picture of what actually needs replacing before you’re under time pressure to plant.
Related Questions
Can I plant the seeds I used for the test if they sprouted?
Yes, carefully — sprouted seeds from a paper towel test can be gently transplanted into soil, though handle the fragile new roots as little as possible during the move.
Does seed storage affect how long seeds stay viable?
Significantly — cool, dry, dark storage (a sealed container in a refrigerator, for example) extends viability well beyond seeds left in a warm, humid garage or shed. Storage conditions can matter as much as the seed’s actual age.
Is it worth testing seeds that are only a year old?
Usually not necessary — most seeds hold strong viability in their first year regardless of type. Testing becomes genuinely useful starting around year two or three, or any time storage conditions were less than ideal.
Related: How to fix leggy seedlings · Seed starting mix vs potting soil
Sourced from: University of Illinois Extension
