Packets of seed for vegetables and flowers often contain more than a gardener needs in a single season, and gardeners end up saving the rest of the packet for the next year. Then these open seed packets get misplaced or forgotten about and may end up being held over for multiple years. Late winter is a good time to dig out the old seeds and check their viability to ensure they are worth planting.

In relation to seeds, viability simply means the ability to grow. Seeds lose viability over time because of age, exposure to extreme temperatures or too much or too little humidity. There is considerable variation among species, but generally seeds with hard coats, like beans, last longer than seeds that are tender, like those of peppers.

Seed viability tests are conducted the same way regardless of the seed type. Gather a paper towel (or a few for multiple lots of seed) and a sealable bag or container.

Wet the paper towel, wring any excess water from it and lay it out flat. If the towel is very thin or tears, place a second one on top of it. Place 10 seeds in a row near the top of the towel, leaving space between them. Then, roll the towel from the right or left side so that the seeds are wrapped into the towel but separated from each other. Place the rolled towel in the bag or container and seal it.

Label the bag or container with the date. If you’re testing multiple lots or types of seed, rolled paper towels can share bags or containers. Just be sure to label them in some way.

Place the sealed bag or container in a warm place such as a sunny window or on top of the refrigerator. Put a reminder on the calendar to check them in seven to 10 days. Most seeds will germinate in this amount of time if they are still viable. Check the seed packet or other resources for specific germination times if unsure.

After 10 days (or less if the sprouts are evident through the towel), unroll the paper towel and see how many seeds sprouted. If all of them sprouted, you can expect the remainder of the seeds in the packet to do so also. If only five seeds sprouted, probably half of the seeds in the packet have lost viability. You can still plant what you have, but expect only half of them to grow.

If you wish to save the seeds used in the germination test, plant them in a seedling tray or other small containers to grow until it is time to transplant them outdoors. If roots have grown through the paper towel, cut it and plant it with the seedling rather than trying to separate them and damaging the roots.

Another option to test viability is a float test. It works best with large seeds such as beans, corn and peas. Simply place 10 seeds in a container of water and wait about 15 minutes. If the seeds float, they are not viable. This gives a percentage of viable seed in the same manner as the sprout test.

For seed lots with low viability rates, you may wish to start the seeds in trays prior to the season and transplant the plants that grow into the garden later. This saves space in the garden and ensures an even stand once transplanted.

— Jennifer Smith works in regulatory horticulture and has worked as a horticulturist for various government entities. She has experience in landscape design and maintenance and as an educator.