How-to Guide
How to Test Seed Viability with a Germination Test
The short answer
To check whether old or saved seed is still good, run a simple paper-towel germination test about a month before planting. Count out at least 20 seeds (50 or 100 is better), space them on moist paper toweling, roll it up, seal it in a plastic bag, and keep it warm at 70 to 80 degrees F.
After 5 to 10 days, count how many sprouted. The percentage that germinate estimates how the batch will perform: a high rate means you can sow normally, while a low rate means sowing more thickly or replacing the seed.
Run the test
- 1Count a sample — Randomly pick at least 20 seeds; 50 is better and 100 gives the most reliable percentage.
- 2Moisten and roll — Space seeds on premoistened paper towels and roll them up so seeds stay separated.
- 3Keep warm — Seal the roll in a plastic bag and hold it at 70 to 80 degrees F.
- 4Count sprouts — Check after 5 to 10 days and count the seeds that have germinated.
Read the result
The share that germinate estimates field performance. If nearly all sprout, sow as if new; if only a portion sprout, sow more thickly to compensate or start with fresh seed.
✔ Test about a month before planting, especially for seed more than a year old or that does not look fresh.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Iowa State University Extension — How to Store Seeds and Test Germination Rates — Roll counted seeds in moist paper towel, keep warm 70-80 F, count sprouts after 5-10 days.
- Oregon State University Extension — Will Your Seeds Grow Plants? — The germination percentage predicts garden performance and whether to sow more thickly.
- Clemson Cooperative Extension HGIC — Are Those Old Vegetable Seed Still Good? — Test germination about a month before planting for old or questionable seed.