Seed Viability

We’ve all ended up with packets of seeds from previous years. Are those seeds any good? Even if they sprout, will they grow into healthy, productive plants?

So many seeds! (Kate Russell)

How long do seeds last, anyway?

I am asked that question every spring. And every spring I tell people, “It depends.”

The answer comes down to viability and vigor.

Seed viability refers to a seed’s ability to germinate under normal conditions. Seed vigor is all about that seed’s ability to successfully grow into a mature plant. The likelihood of a seed being able to germinate coming out of storage depends on the type of plant and the way it was stored. But start by looking at the seed packet.

If you look at a seed packet, you may see a “packed for” date. You may also see a “sow by” date. The “packed for” date tells you the year the seeds were produced and packaged. The “sow by” date tells you the point at which seeds will be less likely to produce strong, vital plants.

Living seeds

Seeds may not look like anything exciting is going on, but they are alive. They are eating and breathing embryonic plants. They just do those things very slowly. Stored starches (endosperm) are consumed and gas exchanges still occur. It isn’t until the seed hull is softened by moisture and heat that the exciting business of germination begins. But how can you help your seeds survive being held in storage and how can you tell if they are any good?

A simple seed drawing (Kate Russell)

Seed food

As each seed is produced, it is given a certain amount of stored energy in the form of starches and sugars. There must be enough stored energy to sustain the seed, give it the resources it needs to germinate, and then grow big enough to start performing photosynthesis. Very often, older seeds will still germinate but they won’t have enough energy to grow into strong, healthy plants.

Sustainable seeds

In 2008, a 1,900-year-old Judean date seed germinated in a lab. That was an extremely unusual case. An ongoing 140-year-old study at Michigan State University has only found one seed (a weed) still viable since the study began. Some seeds last longer than others. Most of the time, seeds are at their best the first year, slightly less so the next year, and so on. After 4 or 5 years, most seeds have used too much of the stored energy to have enough left to grow.

There is a lot of debate about how long seeds will last, even with today’s modern scientific methods. This chart is a merging of data from several sources, with the most conservative numbers used. Your results may vary.

Seed storage

The best way to help your seeds last is to keep them dry and cool. Seed banks use liquid nitrogen, but that probably isn’t on your list of options.

Keeping your seeds dry helps the hull stay intact. Keeping temperatures low slows respiration rates. Optimally, your seeds are best stored at temperatures below 42°F with a relative humidity between 20 and 40%. This makes your refrigerator a good place to store seeds, as long as seeds are protected against moisture.

The downside of using the fridge, besides running out of room, is that refrigerator temperatures and humidity levels change frequently. Condensation happens. You can include one of those desiccating silica packets in your seed containers to reduce the humidity problem. Just remember, too much of a good thing can be a bad thing. Moisture levels below 5% can damage a seed’s vigor. Some people store seeds in the freezer. I don’t have that much room in my freezer and freezers have the same rapidly fluctuating temperature and humidity problems I just mentioned.

​​Personally, I like to believe that nature has already sorted most of this out. I keep my seeds in paper envelopes in a lidded wooden seed box, on a protected porch, exposed to the prevailing temperatures but protected from the rain. To me, this keeps my seeds in tune with the prevailing seasonal changes, ready to get to work as temperatures and humidity levels rise in spring. But that’s just me.

How to test your seeds

So, you’ve been hanging on to those favorite seeds, waiting for the Right Time. How do you know if they are any good? The easiest way is with a paper towel test:

1. Wet a paper towel or paper coffee filter and squeeze out as much water as you can.
2. Place up to 10 seeds on the paper towel.
3. Roll it up or fold it and put it in a sealable bag or plastic container.
4. Be sure to attach a note that includes the plant type, the date the test started, and the average days until germination from the seed packet.
5. Place the bag in a safe, warm spot, above 70F°.
6. Mist as needed to maintain humidity without getting soggy.
7. After one week, check the seeds every day for signs of germination.

Note that some seeds need light to germinate. This group includes chamomile, lemon balm, lettuce, and savory. You can conduct the same test with these seeds, simply leave the paper towel flat, exposing the seeds to light.

Sprouting cantaloupe seeds (Downtowngal) CC BY-SA 3.0

If you test 10 seeds and 7 of them germinate, you will know that they have a 70% germination rate. Generally speaking, germination rates below 70% are not worth planting. Also, this won’t tell you if those seeds have the energy they need to thrive, but you will at least know what to expect in the germination department. And those germinated seeds can be gently planted in soil. Don’t worry if some of the paper is attached. It’ll disappear on its own before you know it.

In fact, you can make planting easy by tearing paper towels into strips and putting drops of non-toxic glue at the proper intervals. Then pour seeds over the strips (in a big container so you don’t lose seeds), give the strips a shake, and lay them flat to dry. Be sure to write the seed type on the paper towel. This works especially well with tiny lettuce seeds that are scattered on the soil surface. The paper toweling holds them in place long enough to start growing, but the glue and paper towel decompose into the soil. This is a fun kids’ activity, too.

Not all seeds will sprout well in a damp paper towel. Peanuts and Malabar spinach, for example, need soil. For these seeds, use a tray filled with wet potting soil. Cover the seeds with vermiculite to help maintain moisture levels. Keep the soil warm and moist. Seeds should germinate in 7–10 days.

Instead of letting seeds die of old age and neglect, take some time to go through your seeds and plant them sooner, rather than later.

This year, I’ve decided to plant every seed I own. I have to stay home anyway, being low on the vaccine list, so it seems like the perfect time. Plus, two friends have given me all their canning equipment!

It’s going to be a busy summer…