How to Do a Paper Towel Germination Test
Roll 10 seeds in a damp paper towel, keep them warm, and count sprouts. Most crops show in 10 days; carrot, parsley, pepper, and onion can take 3 weeks. H...
Published by ThriveThyme
germination test seed viability seed stash seed starting
How to Do a Paper Towel Germination Test
A germination test tells you what share of a packet will sprout. It takes a paper towel, a zip bag, and 10 seeds. Do it now for packets you are unsure about, or about a month before you plan to sow, as Iowa State Extension suggests.
What You Need
- Paper towels or a coffee filter
- A zip-top bag or a plastic container with a lid
- A marker for the bag
- 10 seeds per packet (use 20 or more for a sharper number if the packet is big)
Steps
- Dampen a paper towel. It should be wet but not dripping.
- Lay 10 seeds on half the towel with space between them.
- Fold the towel over the seeds and slide it into the bag. Leave the bag slightly open for air.
- Write the crop, packet, and start date on the bag.
- Keep the bag warm, about 70F to 75F. The top of a refrigerator or near a warm appliance works. Light does not matter for most crops.
- Check every 2 to 3 days. Keep the towel damp. Count seeds with a visible root.
- Make the final count at day 10 for most crops. Wait up to 21 days for carrot, parsley, parsnip, celery, onion, leek, pepper, and asparagus.
How to Read the Result
Sprouted seeds divided by seeds tested gives the germination rate. 7 of 10 is 70 percent.
| Result | What to do |
|---|---|
| 80 percent or more | Sow at the normal rate |
| 50 to 79 percent | Usable. Sow thicker to make up the gap, then thin |
| Under 50 percent | Buy fresh seed for the main planting |
To sow thicker, divide 100 by the rate. At 60 percent, sow about 1.7 times the normal amount.
Carrot, parsley, and pepper often germinate lower than beans or squash even when fresh. A modest carrot result is not always a sign of old seed. Compare with the seed life chart.
Can You Plant the Sprouted Seeds?
Large seeds like beans, squash, and cucumber can go into pots if you handle the roots gently. Small sprouts usually tear. Most gardeners treat test seeds as spent.
Track Tests in the App
The Seed Viability Check has a test log. Start a test, and it shows the final count date for that crop. Enter how many sprouted, and it gives the sow-normal, sow-thicker, or replace call.
Sources: Iowa State University Extension, Nebraska Extension G2090, Illinois Extension.