Testing Seeds for Germination

Betty Jakum
Adams County Master Gardener

Although it is still a bit early, many of us are just itching to begin this yearís gardening season. Being able to safely plant seeds outdoors is still some time away, but now is a great time to order new supplies of seeds and to assess the ones left over from past seasons.

It is not unusual for gardeners to find themselves with half-used and undated packets of favorite flower and vegetable varieties. How to know if these seeds are still viable when they are planted in the garden?

Viability is the seedís capability to grow and develop. One way to test a seedís viability, and thus to avoid wasting time and garden space (if the seeds prove to be no good), is to run a germination test. A germination test is a simple gardening technique that involves nothing more than the seeds, some absorbent paper towels, a spray bottle, water, a zip lock bag and a warm spot.

To begin testing for germination, spread a paper towel on a water proof surface and wet down with warm water, using a spray bottle or some similar spraying device. Donít make the towel too wet. If water beads up around your fingertip when you press on the towel, it is too wet.

As few as ten seeds are usually sufficient to accurately test for germination, although you can use more if you have them. Evenly space the seeds on the paper towel keeping them about two inches from the edges. Carefully roll or fold them up in the towel so they are encased in a long, narrow strip of wet paper and slip the whole thing into the zip lock bag. Seal the bag and mark it carefully, especially if more than one kind of seed or variety is being tested at the same time.

Place the bag in a warm spot. The most rapid seed germination occurs when temperatures remain consistently between 70 and 80 degrees. Suitable places for seed germination in the average home include the top of a hot-water heater or refrigerator, near a wood stove or on a high shelf near a hot-air vent. Make sure the paper towel inside the plastic bag remains damp during the entire testing period, moistening it if it shows signs of drying out.

Make the first germination check after two or three days. Keep checking at regular intervals to note the rate of seed germination. Most viable seeds will germinate within two to three weeks, and some will sprout much sooner. For example, seeds of the cabbage family will often sprout in two days while carrot seeds can take up to three weeks. It has also been my observation that the seeds of cold weather plants like broccoli and cauliflower will sprout earlier than the seeds of more heat-loving plants like tomatoes and peppers if seed-tested in March or April.

The test is completed when the majority of the seeds have germinated and several days have passed since the last sprouting. A germination rate of 70% or more indicates that the seeds are viable and can be planted normally in the garden.

Any number below that should throw up a caution flag. This doesnít mean that the seeds cannot be planted, only that they need to be given some extra considerations.

For one thing, these seeds should be given high priority for planting in this yearís garden as they will only be less viable next year. Some experts say that seeds lose 30% of their viability each year. Another way these seeds can still be used successfully is to over plant them. Using this technique, more seeds are planted in a given space increasing the germination rate significantly.

Seeds with germination rates of 30% or lower should probably be discarded. Not only will the germination rate be low, but even the seeds that do manage to sprout will probably be less vigorous and more prone to pests and diseases.

In deciding whether to use older seeds, it is also a good idea to know the various longevity rates of different seeds. For example, seeds of the cabbage family, cucumber, eggplant, spinach, squash and watermelon can be used up to five years from packaging, while corn is best used within one or two years. Seeds of larkspur, Sweet William, and aster are relatively short-lived, too, and not usually viable after two years. Marigold seeds can last for three years, and zinnia and nasturtium seeds for up to seven years.

The unsettled weather of late March may keep gardeners from working outside, but nowís a great time to get a jump start on the gardening season and check the viability of seeds that will produce this yearís perfect garden.

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