How to Test Leftover Seeds

Test seeds that you’ve saved from last season to see if they are worth planting.

Reader Contribution by The Natural Gardening Company
article image
by Adobe Stock/

Those of us who plant our gardens from seed nearly always have a stockpile of seeds from previous seasons. About this time each year we ask ourselves, “Should I use the seeds I have on hand, or buy new ones?” Tempting as it may be to use last year’s seeds, they are not free. There is a cost in time and effort that comes with planting seeds that fail. At the very least, last year’s seeds can throw you off schedule if they aren’t viable. The simple reality is that you don’t know if your seeds will perform at an acceptable level unless you test them. You can’t tell by looking at them, and you can’t tell by the date on the packet. There are too many variables in the way seeds respond to storage conditions and how long certain varieties remain viable. You need to test.

Testing seeds is easy and inexpensive. All you need are some petri dishes, filter paper, a pair of tweezers and your seeds. A medicine dropper also comes in handy. If you can’t find them locally, petri dishes and filter paper can be ordered online from Indigo Instruments.

In order to get an accurate test you need a sufficient sample of seeds. 25 will do. If you have fewer than 25 seeds, you need to test enough of whatever you have to get a meaningful result, at least 10. You simply put the filter paper in the petri dish, and then place the seeds one by one on the dry paper with your tweezers so they are separated from one another (this makes counting easier later on). Once your seeds are distributed over the paper, carefully drop water in different spots until the moisture spreads throughout the filter paper. You want it moist but not saturated. Too much water will make the seeds rot. Start with a few drops to see how they spread. Add more if the paper is dry.

When you finish these steps, put the lid on the petri dish and affix a label that includes the seed type, number of seeds, and today’s date. When you’ve done this with all the seeds you wish to test, put them in a low traffic location out of direct light where the air temperature is comfortable. A shelf in your kitchen, pantry or office will do.

Generally seeds begin to germinate in 7-10 days, although certain varieties can respond more quickly. Typically, if the seeds are going to germinate, they will do so more or less together, within 2-3 days of each other. After this flush has finished you will have an idea of what to expect when the seeds are planted in soil. If 20 seeds out of 25 germinate you have an 80 percent germination rate. If 15 out of 25 germinate you have a 60 percent germination rate. To get an idea of where to draw the line, take a look at the numbers below which specifies the minimum federal germination requirements for various vegetable varieties:

  • Artichoke: 60
  • Asparagus: 70
  • Asparagus bean: 75
  • Bean, garden:70
  • Bean, lima: 70
  • Bean, runner: 75
  • Beet: 65
  • Broadbean: 75
  • Broccoli: 75
  • Brussels sprouts: 70
  • Burdock, great: 60
  • Cabbage:75
  • Cardoon: 60
  • Carrot: 55
  • Cauliflower: 75
  • Celeriac: 55
  • Celery: 55
  • Chard, Swiss: 65
  • Chicory: 65
  • Chinese cabbage: 75
  • Chives: 50
  • Citron: 65
  • Collards: 80
  • Corn, sweet: 75
  • Corn salad: 70
  • Cowpea: 75
  • Cress, garden: 75
  • Cress, upland: 60
  • Cress, water: 40
  • Cucumber: 80
  • Dandelion:60
  • Dill: 60
  • Eggplant: 60
  • Endive: 70
  • Kale: 75
  • Kale, Chinese: 75
  • Kale, Siberian: 75
  • Kohlrabi: 75
  • Leek: 60
  • Lettuce: 80
  • Melon: 75
  • Mustard, India: 75
  • Mustard, spinach: 75
  • Okra: 50
  • Onion: 70
  • Onion, Welsh: 70
  • Pak-choi: 75
  • Parsley: 60
  • Parsnip: 60
  • Pea: 80
  • Pepper: 55
  • Pumpkin: 75
  • Radish: 75
  • Rhubarb: 60
  • Rutabaga: 75
  • Sage: 60
  • Salsify: 75
  • Savory, summer: 55
  • Sorrel: 65
  • Soybean: 75
  • Spinach: 60
  • Spinach, New Zealand: 40
  • Squash: 75
  • Tomato: 75
  • Tomato, husk: 50
  • Turnip: 80
  • Watermelon: 70

If the seeds you are testing germinate below these standards you should strongly consider buying new seeds.

Certain seed varieties tend to rot when they are tested in this manner. These include pumpkins, melons, beans and peas. The latter two are highly absorbent and will need additional water as they dry out, and this encourages rot. There is no easy way around this. All I can suggest is giving them a try and judging from the results. Also, you may find that beets, chard and spinach are difficult to test. Give them a try to see if you are successful.

Now you know how to do this – it’s time to get started! It may be freezing today but planting season is soon upon us.

Next time we’ll take a look at solarizing your soil, a project which can yield miraculous results.

All MOTHER EARTH NEWS community bloggers have agreed to follow our Blogging Best Practices, and they are responsible for the accuracy of their posts. To learn more about the author of this post, click on the byline link at the top of the page.

Need Help? Call 1-800-234-3368