How to Test Seed Viability and Plant Old Seeds
You found a packet from two years ago at the back of the drawer. Maybe three years. The label says “Best By 2023” and you’re wondering if it’s worth sowing or just wishful thinking. Ten seeds, a damp paper towel, and three days will give you a real answer.
This is the test. It takes five minutes to set up, costs nothing, and tells you exactly how to adjust your planting plan before you waste a cell tray or a row. If you want a broader refresher on seed life and storage before you start, Park Seed’s guide to seed longevity and proper storage is a useful companion read.
What Seed Viability Means
Viability is simple: it tells you what percentage of seeds in a packet are still alive and capable of germinating. That’s the number that determines whether you plant at normal rates, sow more heavily, or order fresh seed.
Storage conditions and species drive how long that number stays useful. Most vegetables hold well for 2 to 3 years. Onions and parsnips are the short-lived ones, so plan on replacing them annually. Tomatoes, cucumbers, and squash are the long haulers, often still strong at 4 to 5 years. If you’re unsure, test before you commit.
If you want a quick benchmark before you start sorting packets, this chart gives you the general lifespan ranges gardeners usually work from.
| Seed Type | Typical Lifespan |
|---|---|
| Onion, parsnip | ~1 year |
| Most vegetables | ~2 to 3 years |
| Tomato, cucumber, squash | ~4 to 5 years |
These are averages. A well-stored tomato seed can outperform a poorly stored one that is only a year old. The test tells you more than the calendar.
What You Need
You don’t need anything fancy. A paper towel or coffee filter, a zip-lock bag, a spray bottle, and a marker are enough. Coffee filters are worth using if you have them because they hold together better and are easier to unroll without tearing roots.
How to Run the Test
The paper towel test works best when the seeds stay evenly damp, warm, and labeled from day one.
Mist the towel until it’s evenly damp. Not dripping. Think wrung-out sponge. Count out 10 seeds and space them across half the towel. Fold the other half over them, label it with the crop and date, and slide it into the bag. Leave the bag loosely open. Seeds need oxygen, and a sealed bag invites mold.
Keep it somewhere warm. 65° to 75° F covers most vegetables. Tomatoes and peppers prefer the higher end, around 75° to 80° F. The top of a refrigerator works well if your house runs cool.
Check daily. You’re looking for a root tip emerging from the seed coat.
Typical windows vary by crop, so it helps to know what “slow” means before you assume a packet has failed.
Count sprouts as they appear so late germinators don’t tangle with earlier ones. Stop when nothing new has emerged for two or three days in a row. If you want more help troubleshooting weak germination before you sow trays, Park Seed’s germination guide is worth keeping open beside you.
Reading the Results
With a 10-seed test, the math is easy because each sprout equals 10%.
- 8 or more sprouts (80%+): Plant at normal rates. This seed is performing well.
- 5 to 7 sprouts (50% to 80%): Still usable. Increase your sowing density to compensate. Divide your target plant count by the germination rate as a decimal. If you want 50 plants and your rate is 60%, sow about 84 seeds. For trays, drop two seeds per cell and thin to the stronger seedling.
- Fewer than 5 sprouts (below 50%): Replace it. A stand this uneven usually isn’t worth the space, especially in a short season.
If Seeds Sprout During the Test
Yes, you can plant them. Hold the seed coat, not the root, and set them root-down into pre-moistened seed-starting mix. Keep them warm and under light. Handle gently because those roots are more fragile than they look.
If you want a steadier setup for transplanting those early sprouters, Park Seed’s One-Step Bio Dome and the how-to article on starting seeds successfully make the handoff from test to tray easier.
See Park’s One-Step Bio Dome
Storing What Passes
Cool and dry conditions extend seed life dramatically. For every 10° F drop in temperature, seed longevity roughly doubles. The same goes for moisture. Short-term, a refrigerator at 35° to 40° F with a desiccant packet in an airtight jar is enough. For seeds you want to keep for years, dry them to low moisture and freeze them sealed.
Label everything before it goes in: variety, crop, year. Future-you will be grateful. If you’re building out next season’s plan at the same time, Park Seed’s guide on what to start indoors and what to direct sow pairs well with a viability check.
FAQs
Can I Just Use the Float Test to Check if Seeds Are Still Good?
No. Seeds float or sink based on density, not viability. A healthy seed can float, and a dead one can sink. The paper towel test is the most reliable method most home gardeners can do without special equipment.
What if None of My Seeds Sprout in the Towel?
Don’t throw them out yet. Some seeds, especially parsley, can take two to three weeks. Others need cold, moist stratification before they’ll germinate at all, so it helps to check the packet and compare your crop with Park Seed’s broader seed-starting guidance before you write off a slow germinator.
What’s the Difference Between Viability and Vigor?
Viability tells you whether a seed can germinate. Vigor tells you how well the resulting seedling will perform under stress. A seed can be viable but low-vigor, meaning it sprouts slowly, unevenly, and weakly. High-vigor seed is what you want in the ground.
How Do I Keep Seeds Moist but Not Moldy During the Test?
Keep the towel damp, not wet. If it’s dripping or the bag is sealed tight, mold risk goes up fast. Squeeze out excess moisture before placing seeds, and keep the bag cracked open for airflow.
What Seeds Need Special Treatment Before I Test Them?
Large or hard-coated seeds, including many squash, beans, and morning glories, benefit from a short soak in room-temperature water before they go on the towel. Some seeds also need light to germinate and should sit on a plate in bright conditions instead of inside a folded towel. Know your crop before you set up the test.
How Old Is Too Old? Is There a Point Where Testing Isn’t Worth It?
For onions and parsnips past two years, it usually makes more sense to order fresh. For most everything else, a quick test takes less time than wasting a seed tray. Park Seed’s vegetable seed packets and current crop pages make it easier to keep your stash organized by season and year.
A short testing session before you place your spring order can reshape the whole planting list and save you the frustration of gaps where a row should have been.