How to Test Seed Germination Before Planting Season

A simple paper towel test that tells you exactly which seeds are still viable so you can plan your garden with confidence.

Why test before you plant

Planting seeds with unknown viability wastes garden space, time, and a full growing season if they fail. A 10-minute germination test done 2-4 weeks before planting tells you exactly what to expect and what to replace.

What you need for a paper towel germination test

Paper towels: Plain white, unbleached if possible. Avoid paper towels with printed patterns or added fragrances.
A sealable plastic bag: Sandwich or quart-size zip-lock bags work well. One bag per seed variety.
Water: Enough to dampen the paper towel without soaking it. The towel should be moist, not dripping.
10 seeds per variety: Using exactly 10 makes the math simple. If 7 sprout, your germination rate is 70%.
A marker and tape or labels: To label each bag with the seed variety and date.
A warm spot: 70-80°F is ideal. Top of the refrigerator, near a water heater, or on a seed heat mat.

Step-by-step: the paper towel test method

Step 1: Dampen a paper towel with water. Wring out any excess so it is evenly moist but not dripping.
Step 2: Lay 10 seeds on one half of the paper towel, spaced about an inch apart so roots do not tangle.
Step 3: Fold the other half of the paper towel over the seeds.
Step 4: Slide the folded towel into a plastic bag. Seal the bag most of the way, leaving a small opening for air exchange.
Step 5: Label the bag with the seed variety, the date, and the number of seeds inside.
Step 6: Place the bag in a warm location (70-80°F). Avoid direct sunlight.
Step 7: Check every 2-3 days. Re-moisten the towel if it starts to dry out. Count and record sprouted seeds.
Step 8: After the expected germination period (see table below), count the total sprouted seeds. That number times 10 is your germination percentage.

Expected germination times by seed type

Most vegetable seeds germinate within 5-14 days at 70-80°F. Some take longer.

3-5 days: Radish, lettuce, cucumber, squash, beans
5-7 days: Tomato, pepper (can take up to 14), broccoli, cabbage, kale, beet, spinach
7-10 days: Carrot, onion, herb seeds (basil, cilantro, parsley)
10-14 days: Pepper (some varieties), parsnip, celery
14-21 days: Parsley (notoriously slow), some flower seeds

What the results mean

80-100% (8-10 of 10 seeds): Excellent viability. Plant at normal seed spacing. These seeds are performing well.
60-79% (6-7 of 10 seeds): Good but declining. Plant extra seeds per hole or row and thin to the strongest seedlings.
40-59% (4-5 of 10 seeds): Marginal. You will need to sow roughly double the normal amount. Consider whether buying fresh seed is more practical.
Below 40% (0-3 of 10 seeds): Poor viability. Buy fresh seed. Planting these will result in patchy stands and wasted garden space.

When to buy new seed instead of planting old

Germination rate alone does not tell the whole story. Here are the factors to weigh:

Seed cost vs. garden space: If the seeds are inexpensive (lettuce, radish, beans), over-sowing is cheap insurance. If the seeds are expensive (hybrid tomatoes, rare varieties), even 50% germination may be worth it.
Seedling vigor: Seeds that barely germinate often produce weaker seedlings. If vigor matters for your crop (transplants that need to be strong), lean toward fresh seed.
Available garden space: Over-sowing to compensate for low germination requires more thinning and takes up space that could go to reliable seed.
Season length: In short-season climates, failed germination means lost time you cannot get back. Fresh seed with high germination reduces that risk.

Tips for getting reliable test results

Test at least 10 seeds per variety. Fewer seeds gives unreliable percentages (one seed = 10% swing).
Keep the paper towel consistently moist. If it dries out, the test is void.
Maintain steady warmth. Cold temperatures slow or prevent germination and skew results.
Check every 2-3 days but do not open the bag constantly. Each opening lets moisture escape.
Use fresh paper towels, not recycled ones that may contain chemicals.
Run the test 3-4 weeks before your planned planting date so you have time to order replacements if needed.

Pair it with a tracking log

Seed Germination Rate Estimator Tool

Seed Germination Test Log Printable

Simple takeaway

A paper towel germination test takes 10 minutes to set up and gives you a clear answer within 1-2 weeks. Test every seed variety you plan to use, especially anything more than a year old. If the rate is below 50%, buy fresh. If it is 50-80%, oversow and thin. Above 80%, plant normally. Knowing your germination rate before planting prevents wasted space, wasted time, and last-minute trips to the garden center.

FAQ

When should I start germination testing before planting season?

Start 3-4 weeks before your planned planting or transplant date. This gives you enough time to run the test (7-14 days for most seeds) and still order replacement seeds online if needed. For spring planting in most zones, late February to mid-March is a good time to test.

Can I plant the seeds that sprouted in the paper towel test?

Yes. Carefully transfer sprouted seeds to soil, placing the root down and covering lightly. Handle them gently because the emerging root is fragile. This works best if you catch them right as the root tip emerges (1/4 inch or so). Longer roots are more likely to break during transfer.

Does the paper towel method work for all types of seeds?

It works for most vegetable, herb, and flower seeds. Some seeds with hard coats (morning glory, sweet pea, nasturtium) benefit from soaking or scarification before testing. Very tiny seeds (like chamomile or begonia) can be difficult to handle on a paper towel but the method still works if you are careful.

My seeds sprouted in the test but failed in the garden. What happened?

Paper towel tests provide ideal moisture and temperature. Garden soil can be colder, drier, or have pathogens that kill seedlings (damping off). If your test shows high germination but garden results are poor, the issue is likely soil temperature, moisture consistency, planting depth, or soil-borne disease rather than seed viability.

How long do common vegetable seeds stay viable in storage?

Under good conditions (cool, dry, dark): onion and leek seeds last about 1 year, corn and pepper 2 years, beans and peas 3 years, tomato and broccoli family 4 years, and cucumber, squash, and melon seeds 5-6 years. These are averages. Ideal storage (sealed, refrigerated) can extend these significantly.