Germination Testing

Germination Testing

By Thomas T. Watson

It seems most of us have a favorite quote from the writings of Thoreau - never has a single author been quoted by so many who understood so little about him. Mine is "Though I do not believe a plant will spring up where no seed has been, I have great faith in a seed. Convince me that you have a seed there, and I am prepared to expect wonders." He was not writing about gardening, but the words have for gardeners a certain truth. Planting seeds is an act of faith, as any gardener will tell you, and the true miracle of a seed is that you can pretty much count on your faith being rewarded (all things being equal from the seed's point of view). It isn't that success is guaranteed, far from it, and that is another thing you can hear from any gardener you meet. But most gardening failures, when you think about it, occur after the seed is up. Given the chance - the proper conditions of light, moisture, and temperature - the seed will at least try. More than that, it will give its all, since for a seed germination is a one-shot thing. Do or die, in the most literal sense.

Seeds are wonders of suspended animation, vehicles for the survival of embryonic plants, but their powers do not last forever. Stored seeds lose viability over time, and how long they last depends on both the type of seed and the storage conditions. A test of faith becomes necessary when you find that you have seed left from awhile back; two years, ten years, however long that packet has been stuck in the refrigerator behind that really old jar of mayonnaise (which is now altogether different from what it says on the label). You can have faith and just plant them, and odds are some will come up. But if you like a well-planned garden this sort of trust can bite you. A ten percent germination rate can leave a lot of bare soil in a flower bed, or lead to a disappointment of broccoli. (Well, some of us would be disappointed.) And aren't peppers sometimes enough of a challenge without taking a leap of faith?

A germination test is a simple gardening technique that can tell you when your faith in a seed is justified, and when it is not. If you are a seed-saver and do not replant the same varieties every single year, germination testing is a necessary part of your system for keeping track of what you have and deciding when to plant it. For example, if you have two varieties of heirloom corn, but only room for one in the garden this year, and one shows a significant drop in viability, you know you should plant that one - grow it out, as the professionals say - to provide yourself with fresh seed for the future.

The pro's use germination tests to insure the quality of the seed we buy. Batches of seed are sampled and checked for purity (is it all really of the same species and variety?), and sets of one hundred seeds at a time are tested under carefully controlled conditions of light, moisture, and temperature. A variety of containers and sprouting media are used, such as plastic trays or petri dishes lined with damp blotting paper or paper towels, or containers of vermiculite, perlite, or sand. Great care is taken to ensure a sterile environment, since fungal or bacterial rots can easily make a mess of things. Seed producers have large amounts of money riding on these tests; this is a big deal for them.

For the gardener a check of seed viability can also be a big deal, but it need not look like one. A common variant of the germination test is called the rolled towel test, often used to check the viability of cereal grains. This is the style of germination test best suited to the home garden, since all you need is a paper towel (or similarly absorbent paper product) and a zip-lock bag. And the seeds to be tested, of course. The paper towel needs to be wet, but not dripping; I use a spray bottle to mist it down until it is as wet as I need, since dipping the paper in water and wringing it out is rough on a paper towel. Believe me when I say that you really want an intact bit of paper for this project. If water beads up around your fingertip when you press on the paper towel, the towel is too wet.

Chose ten seeds from the packet or jar in question and rinse them in a mild solution of bleach (1 part in 10) to rid them of bacteria and fungus spores (otherwise you risk having them rot during the test). Rinse them again with clean water and line the seeds up on the towel about 2 inches from the edge. Roll or fold them up in the towel so that you have them encased in a long, narrow tube or strip of wet paper, and slip the whole thing into the zip lock bag. Seal the bag. Now place the bag in any spot where the temperatures are suitable for germinating that seed.

Wait a day, then start checking for germination. I count a seed as germinated when its radicle (the embryonic root) emerges fully from the seed. Count the number of seeds that have germinated each day and take note of that number, keeping track also of the day. The test is done when all the seeds have germinated, or the maximum time for normal germination has passed (as indicated by the seed packet information or your own experience). If a seed goes moldy, remove it and count it as dead. You should also remove the seeds that germinate as you count them; they are not growing under optimum conditions and might die, and being dead, rot and affect the rest of the seeds in the test.

Add up the number of seeds that germinated. If everything sprouted, congratulations! A 100% germination rate is the best possible news; these seeds have a long life ahead of them. If seven came to life, you have 70% (also not bad), and so on. Anything below 60% should give that seed a high priority for planting this coming season; lower than 40% should be cause for alarm.

The germination rate from the test not only tells you whether or not saved seed is usable, and what priority it should have in you gardening scheme, it guides you in how thickly to sow the seed and what to expect from them. If your favorite paste tomato comes up at 30%, then when it comes time to start the seeds for transplanting in the spring, plant a lot! There is no sense in using such seed sparingly, since at an average viability loss of 30% each year, even fewer of those seeds will come up next season. You should also keep in mind that test results this low mean the plants resulting from such seed will quite probably be less productive than plants grown from "stronger," fresh seed. You will likely see more malformed leaves in the early stages of growth and the plants will be less vigorous and more prone to pests and disease. If that happens, focus on saving seed, not on putting stuff on the table or in the vase. These are especially important considerations for corn, which is pollinated by wind; if the patch comes up sparsely, there will be less pollen sifting down between the plants, and the fertilization rate is likely to be poor. That means disappointing ears and not as much seed for future planting. If the germination rate for your corn is down around 50%, consider planting twice as much seed in a given area, spacing them at half the usual distance, to make up for the empty spots that are bound to develop.

There is, of course, little point to doing a germination test on brand new seed (either from a catalog or last year's crop) unless you suspect a problem. I start thinking of such a test, on average, when the seed is more than two years old. Seed that is stored in a refrigerator (you can freeze seeds, but I only do so if I plan on storing them for a long time) will remain better than 80% viable for at least that long, if kept dry. I've had 75% rates on tomato and pepper seeds after five years of such storage, and yes, I tested them before I planted them.

Is there ever a time when a germination test is not a good idea? Well, if you find you only have 10 seeds left to work with, would you waste them on a paper towel? When it comes down to really small numbers, just plant the things and cross your fingers (and don't let it happen again). And what do you do with those seeds from the test that did sprout? If the seeds are large enough to handle easily (your call!), remove them (forceps help) and plant them carefully into a nice, loose seed starting mix, then gently water them in. Some seeds will survive this treatment, others will not. I try to keep enough of any variety in the jar that I don't feel compelled to save the ten taken for the test, and I definitely don't bother with cutting the sprouts loose if they are from lettuce or carrots! (Makes me go cross-eyed just thinking about it.)

To say that gardening, especially the planting of seeds, can be like an act of faith is not the same thing as leaving such matters to chance. A simple germination test can go a long way toward reducing the element of chance, and gives you important garden planning information. The results of such a test make it much easier to say there is a seed there, and to expect wonders.

About the Author
Thomas Watson is graduate of the University of Arizona College of Agriculture, where he earned a BS in Agriculture, majoring in plant sciences. When he is not writing he is usually working in the garden, re-landscaping his Tucson home, studying botany and plant identification, or "out there" somewhere, studying the natural history of the Sonoran Desert. This is all, of course, based on the assumption that it isn't baseball season, in which case he'll get all of the stuff.

About this Author