BOTTOM LINE Age alone does not determine whether seed is usable. Test a sample under the correct germination conditions, calculate the germination percentage, and sow more heavily when the percentage is low but seedlings are vigorous. |
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What Seed Viability Means
A viable seed is alive and capable of producing a normal seedling when dormancy is overcome and environmental conditions are suitable. A seed that does not germinate in a casual test may be dormant, improperly tested, infected, physically damaged, or dead.
- Viability is the capacity to germinate; vigor is the speed, uniformity, and strength of the resulting seedlings.
- A germination test usually measures both viability and the suitability of the test conditions.
- For wild, native, woody, and many perennial species, dormancy treatment may be essential before a test is meaningful.
Quick Home Germination Test
- Choose a sample: Use 10 seeds for a rough check, 25 for a useful home estimate, or 100 for an easy and more reliable percentage. Sample from different parts of the packet or container.
- Prepare: Place seeds on a damp—not dripping—plain paper towel, coffee filter, or germination paper. Fold it over the seeds and place it in a labeled, partly closed plastic bag or covered container.
- Use species-appropriate conditions: Provide the correct temperature, light or darkness, and any required scarification, soaking, warm stratification, or cold-moist stratification.
- Keep evenly moist: Do not allow drying or waterlogging. Check daily or at the normal interval for that species. Remove moldy seeds only after noting them.
- Count normal seedlings: At the end of the species' expected germination period, count seedlings with sound roots and shoots. Abnormal or severely decayed seedlings do not count as successful germination.
- Calculate: Germination percentage = (number of normal seedlings Ă· number tested) Ă— 100.
Example | Calculation | Result |
|---|---|---|
21 normal seedlings from 25 seeds | 21 Ă· 25 Ă— 100 | 84% germination |
6 normal seedlings from 10 seeds | 6 Ă· 10 Ă— 100 | 60% germination |
How to Interpret the Result
Germination | Practical decision |
|---|---|
85–100% | Good lot. Sow at the normal rate. |
70–84% | Usable. Divide the desired number of seedlings by the germination fraction; at 70–84%, approximately 19–43% extra seed is needed before allowing for later losses. |
50–69% | Marginal. Sow heavily; use for noncritical plantings; retest if the sample was small. |
Below 50% | Usually replace. Keep only if seed is scarce, valuable, or difficult to obtain; sow separately and densely. |
0% | Do not declare it dead until temperature, moisture, test duration, and dormancy requirements have been checked. |
SMALL-SAMPLE CAUTION With only 10 seeds, each seed changes the result by 10 percentage points. If the decision matters, retest with 25–100 seeds. |
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Adjusting the Sowing Rate
To compensate for reduced germination, divide the desired number of plants by the germination rate written as a decimal.
Desired seedlings | Test result | Minimum seed to sow |
|---|---|---|
20 | 80% (0.80) | 20 Ă· 0.80 = 25 seeds |
20 | 60% (0.60) | 20 Ă· 0.60 = 34 seeds (round up) |
Allow an additional margin for transplant losses, pests, damping-off, and field conditions. A laboratory or towel-test result is not a guarantee of establishment outdoors.
Typical Home-Garden Planning Ranges
These are rough expectations for reasonably dried seed kept cool, dry, dark, and stable. Seed may remain viable longer—or fail sooner. Test older seed instead of discarding it solely by age.
Approximate range | Examples and cautions |
|---|---|
About 1 year | Onion, leek, parsnip; often short-lived in ordinary home storage. |
About 2 years | Sweet corn, okra, parsley, spinach; storage quality strongly affects results. |
About 3 years | Bean, pea, carrot, celery, pepper; many remain useful beyond this under good storage. |
About 4 years | Tomato, eggplant, cabbage-family crops; commonly moderate to long lived. |
About 5+ years | Cucumber, melon, squash, lettuce; frequently long lived when kept dry and cool. |
Highly variable | Flowers, native plants, grasses, trees, and shrubs. Dormancy can mimic loss of viability; use species-specific protocols. |
Storage That Preserves Viability
- Dry: store only properly dried seed. Moisture is usually the greatest controllable cause of deterioration.
- Cool: use a consistently cool location. Refrigeration can help when seed is dry and sealed; avoid repeated temperature cycling.
- Dark: protect seed from direct light.
- Sealed and labeled: use airtight containers for dry seed; record species, cultivar, source, harvest or purchase year, and test date/result.
- Condensation control: let a sealed cold container warm to room temperature before opening it.
- Pest-free: keep rodents and insects out; discard seed with extensive feeding damage or contamination.
Important Exception: Recalcitrant Seed
Most common garden seeds are orthodox: they tolerate drying and cool storage. Some species—especially certain tropical trees and several moisture-sensitive woody plants—produce recalcitrant seed that is injured by drying or freezing and must be sown fresh or kept under species-specific moist conditions. Never assume every seed belongs in a dry refrigerator.
Why a Test Can Fail Even When Seed Is Alive
Possible cause | What to check |
|---|---|
Dormancy | Need for cold-moist or warm stratification, scarification, after-ripening, soaking, smoke treatment, or alternating temperatures. |
Wrong temperature | Species-specific minimum, optimum, and alternating day/night requirements. |
Wrong light condition | Some seeds require light and should remain on the surface; others germinate better in darkness. |
Too wet or too dry | Waterlogging blocks oxygen; drying can stop or kill emerging embryos. |
Test ended too soon | Some species germinate in days; others require weeks, months, or more than one seasonal cycle. |
Pathogens or damage | Mold, insects, cracked seed coats, heat injury, or poor development at harvest. |
Other Viability Methods
- Cut test: a firm, well-filled embryo is encouraging, but appearance alone does not prove life.
- Tetrazolium test: a trained laboratory stains living tissue and can estimate viability quickly, including dormant seed. Interpretation is species-specific.
- X-ray or float tests: useful for certain species or screening empty seed, but neither universally proves viability. The popular float test is unreliable as a general pass/fail test.
Record for Each Seed Lot
Record | Entry |
|---|---|
Species / cultivar | ________________________________________________ |
Source and lot number | ________________________________________________ |
Harvest or purchase year | ________________________________________________ |
Storage conditions | ________________________________________________ |
Test date and sample size | ________________________________________________ |
Pretreatment and test conditions | ________________________________________________ |
Normal seedlings / germination % | ________________________________________________ |
Decision | Normal sowing / sow heavily / retest / replace |
Keep or Discard?
- KEEP when germination is acceptable, seedlings are vigorous, and the seed is clean and correctly identified.
- RETEST when the sample was small, the method may have been wrong, or dormancy is likely.
- DISCARD when seed is moldy throughout, heavily insect-damaged, contaminated, mislabeled beyond useful identification, or repeatedly tests poorly under verified conditions.
- Never compost seed known or suspected to carry regulated pests, serious seed-borne disease, or invasive plants; follow local disposal guidance.
RULE OF THUMB Test ordinary garden seed; do not rely on the packet date. For native and perennial seed, check the dormancy protocol.