How to Germination Test Your Seeds

IMG_0685-2Looking through the seed packs of seasons past, it’s not always easy to know which seeds will reliably germinate. And which seeds to buy for the coming season. Here are some tips on how to test your seeds so you know which will be most productive and abundant for you.

Count out an exact number of seeds. We usually count at least 100, making the math easy: if 89 sprout and 11 don’t, you have 89% percent germination. Make sure you test at least 10 seeds, but the more seeds you test the more accurate your results will be.

Wrap your freshly-counted seeds in a moist paper towel, tuck them in a plastic bag and seal the bag. Label the bag with variety, seed count and date the test began. Keep the bag in a consistently warm place in your house (60-70 degrees F).

After a week, open up the bag and count the seedlings. Some seeds take longer to germinate than others; some seeds require unusual conditions to germinate, as well. But most garden seeds will sprout with this simple test within a week. And by the second week you’ll certainly have a sense of whether or not they’ll be reliable once the snows melt.


A couple of the common pitfalls


Relatively consistent 60-70 degree temperatures will suit many seeds. If seed is too cool (below 55 degrees F), it may not germinate. There are exceptions: claytonia germinates even in the refrigerator!

If seed is too warm (above 80 degrees F) germination also decreases. Brassicas and spinach are especially hesitant to germinate in warm conditions. Some crops, like lettuce and kale, germinate best when they chill in a refrigerator for three days prior to becoming moist. Other varieties (like our Habanada pepper) germinate best in temperatures that fluctuate 15 degrees F with a day/night cycle.


If seed is too wet, or especially too dry, they will not germinate well. Fortunately, moisture issues are generally easier to diagnose than temperature issues. A spray bottle is handy to moisten any paper towels that are too dry. Some common crops have moisture preferences you might not expect! Cucumbers, for example, prefer to germinate on the dry side.

And one more idea if you’re struggling

Potassium Nitrate (KNO3)

Some seeds prefer to grow in soil rather than a moist paper towel, period. For these we spray with a dilute solution of KNO3 (also called saltpeter) to simulate the chemistry they experience in soil that inspires them to germinate. For some seeds, this softens the seed coat in a way water would not; for others it breaks their dormancy. Tomato, parsley, chard and pepper are all crops we germination test with KNO3. Important note: it is possible to get a good germination test off these crops without KNO3. But if you are struggling, you now have an idea of how to troubleshoot.

Categories: Home Garden, Seeds, Tips | 4 Comments

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4 thoughts on “How to Germination Test Your Seeds

  1. Marc

    This is a great post. I experiment with aquaponics and germination success in my seed starting attempts has varied widely. I appreciate very much the tips for success. I think I will start some tests on the huge collection of seeds I have from the past two years.

  2. Martin

    Can you be more specific about the KNO3…what strength of chemical how much is added to how much water?


  3. Dorothee

    One thing is rather funny to me: I don’t have a 100 seeds and if I would use 10 for the test, I probably would not have any or enough left to use the seeds in the spring. I think I’ll stick with what I usually do: I use old seeds early in the spring to see if the weather is warm enough for seeds to germinate. I start with the most cold resistant seeds and add the next ones week by week. This year, I got lucky and no late frost harmed my early starters. Actually, the kale seeds I threw out in April this year grew great plants that are still strong and healthy in my garden and – it is true – the kale is better than ever! However, I live in North Carolina and besides some frost at night, we have sunny warm days.

  4. martin

    how much kno3 do you add? what is the mix? thx..

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