Germination Testing

Germination testing is an extremely simple, and important, thing to do for all home gardeners who are saving their own seed. It’s easy, quick, and will let you know how well your seeds will germinate, eliminating the need for over- or re-sowing your seeds when it comes time to start them in the spring.

The whole purpose of germination testing is to see how viable your seed is. This is especially necessary if you rotate your plants every year – saving seeds for planting two or even three years in advance. Rather then frustrating yourself by planting only a few seeds, to find in a few weeks they haven’t come up (thus setting your whole process of seed starting back a few weeks), by germination testing your can prepare yourself by learning how many seeds you should plant in order to keep on your seed starting schedule.


  • Seeds for testing
  • Paper towel
  • Zipper bag (ie. Ziploc)
  • Spray bottle

Fortunately, germination testing takes very limited space and effort. First thing’s first: gather your seed. The larger number you can devote to testing is best, but as an absolute minimum, test 10 seeds of each variety. Any less and your estimation of viability won’t be very accurate. The higher number of seeds you can test (20, 30, etc.), the better your estimation will be.

Remember, if there is any special process your seed must go through to germinate in the first place (cold stratification, for example) to do that first, so your germination numbers are not skewed.

  1. Wet your paper towel. It should be evenly damp, but not dripping wet. The higher quality you can get the better, because you will be lifting it open several times in order to see if your seeds have germinated. It’s frustrating to have it completely falling apart on you by the second or third day.
  2. Gather your seeds and place them in the paper towel, not touching, so you can clearly see which have germinated.
  3. Fold the paper towel in half, over you seeds, to allow them to be completely covered.
  4. Place the seeds in one of your zipper bags and seal completely. This is to keep moisture in. Be sure to write with permanent marker on the bag what plant and variety you’re testing, as well as when you started the test.
  5. Place the bag somewhere warm, as germination is usually hampered by cool temperatures. On top of a fridge or microwave is good area, or anywhere in the house where it’s warm.
  6. After the first day (and every day following) you’ll be checking your seeds. Open the zipper bag, and first check the moisture level of your paper towel to ensure it hasn’t dried out. If it’s feeling dry, spritz with the water bottle. The next thing you’re checking is to see if any of the seeds are germinating. You’ll notice a radicle (the small embryonic root) emerging from the seed coat. Generally this will occur anywhere between 2-14 days, depending upon your temperature and moisture levels. For each little radicle you see, that’s one seed germinated.

The test will be done either when all the seeds have germinated (100% germination rate) or when the maximum amount of time has lapsed for your seeds normally to germinate (it will say this on the back of your seed packet – for example, tomatoes generally germinate in 7-14 days, so after two weeks the test would be done, even if some seeds haven’t germinated).

Understanding the Numbers
To obtain the percentage of seed that is viable, simply divide the number of seed that actually germinated by the number of seed you tested. 10 ÷ 30 = 0.33 (or 33%). 10 is your number of seeds that germinated, and 30 is the number that you originally started out with in the test.

If your germination rate is at or above 70% – that’s a healthy number, and the seed can be stored for another year (cool storage would be suggested to avoid any more further degradation of the seed).

If the germination rate is below 70% but above 50% think about planting those seeds this year so you can replenish your seed supply. If you absolutely cannot plant them this year, store in cool storage until next year.

If your germination rate is below 50% plant them right away, because with another year you’re looking at not having any more seed be viable, as seed viability degrades exponentially. Be sure to over plant if you can, sowing more seed then you think you’ll need, to make up for the lower germination rates.

Is it necessary to test fresh seed?
For fresh store-bought seed, generally not unless you suspect a problem (perhaps none have germinated for you in your typical seed-starting methods). If you have self-saved seed from the previous year, even if it is only a year old, I would suggest testing your germination rates. It’s better to know if your seed-saving methods were successful (and in some cases, they might not have been – it happens to us all at some point) then to potentially waste time on seed that has very low or no germination at all.

What if you only have ten (or less) of a given seed?
You can pre-germinate them with the above method and transfer them to your growing medium after they have germinated, or you can plant them all and hope at least one comes up if the seed is particularly old. Worse comes to worse, you have to purchase new seed for the next year.

Please refer to the table on standard storage times for different seed types here.

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