Viability of Seed

The viability of seeds is a common concern of home gardeners. Most of us get a little carried away in spring with the sight of new plants in the stores and rows upon rows of seed packets. It’s too easy to pick up a packet of peas, and then carrots, and then corn, and then before we know it we have more seeds than we can plant. Some of them end up in a shoebox or forgotten drawer until they’re discovered the next spring or even years later. The first question that pops to mind when we find those packets is, “I wonder if these seeds are still good.”

Seed viability is all about how many of the seeds are alive and will grow into plants. It varies based on the type of seed and how it was stored. Most seeds are intended to be planted the year they’re packaged and you’ll see that date printed on the seed packet. You can expect close to 100 percent viability in that first year. This year, initial results show that just about every tomato seed I planted has sprouted.

My young tomato seedlings

Seed viability is usually identified as a percentage. Each year fewer and fewer seeds will germinate and there is less viability. The most accurate way to determine viability is with a germination test. This is something you can do and something I would recommend before you toss the seeds out.

In a laboratory setting you might start with 100 or 200 seeds for your test, but for a typical home test I suggest using 10 seeds. Randomly select 10 seeds from the packet of seeds you’re wondering about. Put a paper towel or coffee filter on a plate and place the seeds spaced apart on top. I use a paper towel.

Seeds laid out

Add another filter or paper towel on top or just fold over the same one. Wet the paper and seeds until well moistened. The seeds are now ready to begin germinating. You have a few options at this point. You can loosely roll up the paper towel or leave it flat.

Wetting the seeds

The seeds need to be labeled so you know what you’re germinating. I prefer to place each set of 10 seeds into a plastic food bag that is labeled. You can also place multiple rolls of seeds into a large bag; in that case make sure each roll is labeled.

The seeds will still need oxygen so poke a few holes in the top of the bag or leave the end slightly open. You don’t have to use plastic bags, but it’s important that the seeds remain moist and the plastic helps maintain that. It’s easy for the seeds to dry out and given our busy schedules we may not be able to add moisture when we need to.

Seeds in bag and labeled

Place the seeds in a warm spot out of direct sunlight. If the seed packet tells you how many days until germination, you can mark that on the label and come back to check within that time. If you’re not sure how long it will take, you’ll need to check the seeds after five or six days and again every few days after that. What you’re looking for are signs that the seeds are sprouting.

When you’re ready to determine the viability, after indication that germination has taken place, open the paper towel and count the seeds that have little white growths popping out. The math should be easy if you use 10 seeds for your test; the number of germinated seeds tells you the percentage. If eight seeds germinated then you have 80 percent viability, if you had five seeds sprout then you have 50 percent viability. In my test of 10 old squash seeds, three seeds had fully germinated with little roots and two more were showing signs of new white growth, for a 50 percent viability.

Seeds 10 days later

What this means for me is that I can still plant the seeds from this packet, but I need to plant twice as many as I need. The packet directions say to plant five seeds over a 12-inch tall hill and thin to the three strongest seedlings. To achieve the same result, I should sow about 10 seeds.

Old seeds may also be dormant or dead. When you do your viability test the dormant seeds should swell or remain hard once they get the boost of water. Dead seeds will flatten, soften, and may begin rotting. The dormant seeds can still germinate when all of the conditions are good, they may just need extra care. The five seeds in my test that didn’t germinate were plump and showed no signs of decay. Given warmer conditions and more time they may still germinate.

You will probably have leftover seeds each year after planting. Rather than throw them in a shoebox, save them to reuse. By doing it right you can increase viability. You want to store seeds in cool, dark, dry locations. Left in a shoebox on a shelf, vegetable seeds may only remain viable for one or two years; temperature and humidity fluctuations can spell doom for them. If you want to keep seeds for more than a year, put them in a sealed jar with a package of desiccant, those little packets that come with shoes, electronics, and many other products. Place the jar in the refrigerator or freezer.

When frozen, with humidity below eight percent, many seeds will remain viable for decades. The National Seed Storage Laboratory in Fort Collins, Colorado, was built in 1958 to store seeds and test for seed viability. The name was changed in 2002 to the National Center for Genetic Resources Preservation. Their collection includes more than 500,000 seed samples of nearly 7,000 species. The seeds are stored at a temperature of minus 18C degrees. They regularly test the seed viability and replace samples that fall below 60 percent.

Home gardeners certainly can’t match their expertise, but when properly stored you can extend the life of seeds by many years. When it comes time to plant, you can guess at their viability or conduct your own home test. It’s a great way to save money by not buying new seeds every spring.


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