If you save seed from year to year, whether it be leftover bought seed or you are gathering and saving seed from your plantings, you should make a habit of testing the germination rate of any saved seed before you plant. Testing can save a lot of frustration and angst further down the timeline.
It isn’t hard to perform germination testing. Testing germination doesn’t take a huge amount of seed or space and no special equipment. Germination testing will also give you a lot of feedback about your seed saving strategies and methods.
The Paper Towel Test
Soak a couple of sheets of paper towel or coffee filter in water. I like to use 20 seeds to do my tests. Spread the seeds over one half the damp paper towel or coffee filter and then fold the other half of the damp paper over the seeds. Now, roll it up. Don’t make it to tight, but it should hold the seeds firmly in place. Put the rolled-up paper towel and seeds into a clear plastic bag or airtight container. You don’t want the paper to dry out. Keep the airtight container where the temperature will be a constant 55 to 75 degrees F. You don’t need to worry about light.
Open the paper towel in 3 to 5 days and look at the seeds. Count the number that have germinated and record the number in your garden journal. Remove the seeds that have sprouted. Only count those seeds that have sprouted a healthy root and shoot. Leave the unsprouted seed. Spray the seeds and paper towel with water and roll it back up and place it back in your airtight container. Repeat the time sequence until you are satisfied that the remaining seeds are not going to germinate.
Total the number of seeds that germinated and calculate the percentage. For first-year seeds, I consider anything over 80% a total success. As seeds get older, the percentage that germinates will drop. When I can’t get 50% of the seeds to germinate, I generally toss the seeds.
Some seeds won’t sprout in wet paper towels. Malabar spinach is one that comes to mind. For these, I like to use a small seed tray and wet potting soil. Doing this test may present some challenges as the potting mix must remain consistently damp but not soaked and the temperature must be in the range that the seed requires to germinate.
In some cases, you may need a warming mat to accomplish this test. Every few days, check the tray. Count the number of seeds that have sprouted, note that number in your garden journal and then clip the sprouts off at ground level. When no more new sprouts appear within a few days of the last count, total the number of seeds that germinated and calculate your germination rate.
Plastic Container Testing
There are a few seeds that require light to germinate. To test these seeds, use a clear plastic container. Line the bottom of the container with a paper towel. Wet the paper towel but do not leave any standing water. Spread your seed evenly over the paper towel and then close the lid tightly. The container should be placed where it will stay warm, but not get direct sunlight. You don’t want to cook the seeds. Again, check it after a few days and count the number of seeds that germinate, remove the seeds leaving the ungerminated ones. When nothing new is sprouting, calculate your germination rate.
Some seeds need a period of moist cold (called stratification) to germinate. Set up your test of these seeds and place the container in the refrigerator and leave it according to the variety of seed you are testing, then put it in a warm place.
Some seeds, particularly tree seeds or gourd seeds, need to be scarified before planting. You can do this by nicking the hard outer shell of some tree seeds, lightly sanding the seed covering of others. Some success has been reported by placing a quantity of seed in a jar and shaking it vigorously.
Tomatoes, peppers, and some flowering species require potassium nitrate to germinate. Add two grams of potassium nitrate to a quart of water and use this to moisten your test seeds.
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