Last Updated on October 9, 2026
Paper Towel Germination Test: How to Test Old Seeds
To test seed germination, roll at least 20 seeds in a damp paper towel, seal it in a plastic bag, keep it at 70 to 80°F, and count how many sprout. Seeds sprouted divided by seeds tested, times 100, is your germination rate. That is the method Iowa State University Extension gives, and it calls 90 percent or more very good and 50 percent or lower too low to be worth using.
All it takes is a paper towel, a bag and a week or two. My seed viability chart covers how many years each crop’s seed usually lasts; this page is the test itself, the math, and how many seeds to sow once you have your number.
How to do a paper towel germination test
- Count out the seeds at random. Iowa State says at least 20 seeds, 50 is better and 100 is best. Do not pick out the damaged, discolored or light seeds first; the University of Alaska Fairbanks Cooperative Extension says culling them will bias the test.
- Dampen the towel. Make it thoroughly damp but not dripping. UAF suggests a plant mister.
- Space the seeds and roll it up. Lay the seeds in rows so they do not touch, then roll or fold the towel so they stay separated.
- Seal and label. Put the roll in a plastic bag or container so it cannot dry out, and write the crop, variety and date on it.
- Keep it warm. Iowa State says 70 to 80°F. University of Illinois Extension suggests the top of the refrigerator, as long as you do not forget it there. Keep it out of direct sun; UAF notes the heat it adds can throw off the 70 to 80°F target.
- Check early, then daily. Iowa State says to look after two or three days and every day after that for about a week. A seed counts as germinated when a root or seed leaf pushes through the seed coat.
- Count when the sprouting stops. Once some seeds have sprouted and another week brings no more, do the math below. Slow crops in the table further down need longer.
The germination percentage formula
Germination rate (%) = seeds that sprouted ÷ seeds tested × 100
Worked example: you test 20 tomato seeds and 15 sprout. 15 ÷ 20 = 0.75, and 0.75 × 100 = 75 percent. With 10 seeds the math is even easier, which is why Illinois Extension says most people test 10: 8 sprouted out of 10 is 80 percent.
The trade-off is precision. In a 10-seed test every seed moves the result by 10 points, in a 20-seed test by 5 points, and in a 100-seed test by 1 point. UAF Extension notes that how reliable a home test is depends on how many seeds you test. A 10-seed test is fine when the packet is nearly empty; when you have seed to spare, Iowa State’s 50 or 100 gives a sharper number.
What your result means
| Seeds that sprouted | What to do |
|---|---|
| All of them | Plant as normal (Illinois Extension). |
| 90% or more | Very good for most crops (Iowa State). |
| 70% to 90% | Still use it, but sow a little heavier than normal (Illinois Extension). |
| Over 50% but under 70% | Borderline. Illinois Extension suggests new seed below 50 to 60 percent. |
| 50% or lower | Buy new seed. Too low to be worth using for nearly all crops (Iowa State). |
Iowa State adds two useful checks. Small or plentiful seed can be perfectly fine at 70 to 80 percent. And if the packet has a germination rate printed on it from when it was packed, a result still close to that number is worth sowing.
Packets that meet the federal minimum are not required to print a rate, so plenty carry none. Under the Federal Seed Act rules, vegetable seed in packets of a pound or less that meets the federal minimum does not have to print its germination percentage. Seed below the minimum must say “Below Standard” and show its percentage. The minimums are in the last column of the table below, and they show how far below 100 percent a packet can legally be.
Illinois Extension also points out that a seed’s ability to grow a vigorous seedling often declines before its ability to sprout, so an old packet can pass the towel test and still give you weak seedlings. A borderline result is a reason to sow extra, not a guarantee.
How long to wait, by crop
Seed packets often list days to germination, and Illinois Extension says many seeds germinate within 7 to 10 days. The table below adds the slower crops, the official test length, and the federal minimum, so you know what a packet is legally allowed to say.
| Crop | Days to emerge, 68°F soil | Days to emerge, 77°F soil | Official test length (days) | Federal minimum germination |
|---|---|---|---|---|
| Beans, snap | 11 | 8 | 8 | 70% |
| Beets | 6 | 5 | not listed | 65% |
| Cabbage | 6 | 5 | 10 | 75% |
| Carrots | 7 | 6 | 14 | 55% |
| Cauliflower | 6 | 5 | 10 | 75% |
| Celery | 7 | little or none | not listed | 55% |
| Corn, sweet | 7 | 4 | not listed | 75% |
| Cucumbers | 6 | 4 | not listed | 80% |
| Eggplant | 13 | 8 | not listed | 60% |
| Lettuce | 3 | 2 | 7 | 80% |
| Melons (muskmelon) | 8 | 4 | not listed | 75% |
| Okra | 17 | 13 | not listed | 50% |
| Onions | 5 | 4 | not listed | 70% |
| Parsley | 14 | 13 | not listed | 60% |
| Parsnips | 14 | 15 | not listed | 60% |
| Peas | 8 | 6 | 8 | 80% |
| Peppers | 13 | 8 | not listed | 55% |
| Radishes | 4 | 4 | 6 | 75% |
| Spinach | 6 | 5 | 21 | 60% |
| Tomatoes | 8 | 6 | 14 | 75% |
| Turnips | 2 | 1 | 7 | 80% |
| Watermelons | 12 | 5 | not listed | 70% |
Days to emerge at 68°F and 77°F soil: my germination temperature chart (J.F. Harrington’s UC Davis data), rounded to whole days; they tell you roughly when to start looking, not the paper towel result. Official test length: the germination period in UAF Extension’s seed test guidelines, the full time a formal test runs. Federal minimum germination: the standard for vegetable seed sold across state lines, from 7 CFR 201.31.
A few crops need different handling. UAF tests spinach at 59°F with the towel kept on the dry side, and lists lettuce and tomato as needing light, so leave those tests in a bright spot rather than a dark cupboard. Celery shows little or no emergence at 77°F soil in the chart but emerges in about 7 days at 68°F, so keep a celery test near 68°F rather than warmer. Parsley and okra are slow even when warm, about two weeks, so do not give up on them after the usual week. UAF lists turnip together with canola.
How many seeds to sow after the test
Divide the number of plants you want by your germination rate. For 24 plants from seed that tested 75 percent, 24 ÷ 0.75 = 32 seeds. That works for direct sowing, or for sowing one seed per cell in 32 cells.
The other choice is more seeds per cell. With a 75 percent rate, a cell with one seed has a 25 percent chance of staying empty. With two seeds, both have to fail, so 0.25 × 0.25 = about 6 percent. With three, it is under 2 percent. University of Minnesota Extension says to plant two or more seeds per cell when using older, lower-germination seed, then cut all but the healthiest seedling off at the soil line with scissors once true leaves appear. Sow fresh seed one per cell. My seed starting guide plants two seeds per cell and snips the weaker one the same way.
Enter your test result below to see both options.
Germination rate: 75%. Still worth sowing. University of Illinois Extension says to sow a little heavier than normal at 70 to 90 percent.
Direct sowing, or one seed per cell: sow 32 seeds to expect about 24 plants.
| Seeds per cell | Cells left empty, on average | Empty cells out of 24 | Seeds used |
|---|---|---|---|
| 1 | 25% | 6 | 24 |
| 2 | 6.3% | 1.5 | 48 |
| 3 | 1.6% | 0.4 | 72 |
| 4 | 0.4% | 0.1 | 96 |
The empty-cell share is (1 − rate) multiplied by itself once for each seed in the cell. These are averages, so a real tray can come out a cell or two either way. Pick the row whose empty-cell count you can live with.
Troubleshooting a test
- The seeds rotted. The towel was too wet, says UAF. Remove the extra water so it is damp, not dripping.
- The towel dried out. The bag or container was not sealed.
Two more things to watch for. Iowa State says seeds that are normally smooth, round or plump germinate poorly when they are pocked or wrinkled (peas and corn are wrinkled by nature, so that is normal for them). And if nothing sprouts at all, most vegetables do not need cold treatment, but Illinois Extension notes some flowers, such as milkweed and purple coneflower, need cold, moist stratification first.
The sprouts are not wasted. Iowa State says germinated seeds from the test can be planted in cell packs or peat pots, or in the garden if the timing is right, as long as you handle them very carefully; a damaged root or shoot will not survive.
When to test, and what to do if the seed fails
Iowa State suggests testing about a month before you plan to plant, which leaves time to replace a packet that fails. To find that date, look up your frost dates on Plan My Garden, then use my seed starting calendar to count the weeks from your last frost to each crop’s start or sowing date.
If a packet fails, replace it. Wood Prairie Family Farm sells organic vegetable seed, and code PMG5 takes 5 percent off. Then store the new packets cool, dry and labeled with the year so next year’s test is easy. My seed organizer post shows how I keep mine sorted.
Quick questions
How do you test seed germination with a paper towel?
Count out at least 20 seeds at random, roll them in a damp paper towel so they do not touch, seal the roll in a plastic bag and keep it at 70 to 80°F. Check after two or three days and then daily, and count the seeds that have pushed out a root or seed leaf. That is Iowa State University Extension’s method.
How do you calculate germination percentage?
Divide the number of seeds that sprouted by the number you tested and multiply by 100. If 15 of 20 seeds sprout, 15 ÷ 20 = 0.75, so the germination rate is 75 percent.
How long does a paper towel germination test take?
About a week for most vegetables. University of Illinois Extension says many seeds germinate within 7 to 10 days. Slow crops take longer: parsley and okra need about two weeks to emerge even in warm soil, and the official test period for spinach in UAF Extension’s guidelines is 21 days.
What is a good germination rate for vegetable seeds?
Iowa State University Extension calls 90 percent or more very good for most crops, says 70 to 80 percent is fine for small or plentiful seed, and says 50 percent or lower is too low to be worth using for nearly all crops.
Can you plant seeds that sprouted in a paper towel?
Yes, if you handle them very carefully. Iowa State University Extension says sprouted test seeds can go into cell packs or peat pots, or into the garden if the timing is right, but a damaged root or shoot will not survive.
Know your seed count, then let the planner count the plants
Your germination test tells you how many seeds to sow for each plant you want. Plan My Garden is free to start: enter your zip code, draw your beds, pick the crops you just tested and everything else you want to grow, and it places each plant at square-foot spacing and builds a planting schedule (start indoors, transplant and direct sow dates) from your frost dates.
Related: Seed Viability Chart · Seed Germination Temperature Chart · Seed Starting Calendar · The Best Seed Organizer
