How can you tell if a seed is still viable? Here are three reliable seed germination tests you can take to see if there is life left in your old seed packets.
If you are like me, you have several old packets of seeds left over from gardening years past. If they are from last year, there probably will not be an issue with seed germination rates, and you are safe to plant.
But it the seeds are more than a two years old, you should consider doing one of these three reliable seed germination tests before you plant your garden.
Objective of seed germination test
Let’s say you found a package of your favorite bean seed, which is usually good to use for up to three years. Its four years past the plant by date, but you hate to throw them away if it’s not necessary.
The object of the germination test is to know the maximum germination possibility of your old seed packets. This information can be used to compare the quality of different seed based on their age and also estimate the planting value of a seed packet.
A germination test is often the only test a gardener can conduct on the seed to determine if it is suitable for planting. When you store seed in a traditional home setting, the germination rates deteriorate rapidly because of moisture in the home. By knowing the germination rate, you can adjust your planting rates to get the desired crop in the garden.
How to calculate seed germination rate
To calculate germination percentage, divide the number of healthy seedlings by the total number of seeds in the test and multiply by 100.
For example, if you started with 15 seeds and had 12 healthy sprouts, your germination rate would be 80%. The lower the germination rate, the sooner the seed should be grown. If your germination rate is less than 60%, consider buying new seeds or sowing your seeds extra thickly to compensate for the low germination rate.
You can perform this test with as little as 10 seeds, but the fewer number if seeds used the less accurate the germ rate.
Related searches: Types of germination test, Seed germination test paper towel, How to tell if seeds are good or bad
Some seeds will germinate best after a period of moist cold which mimics the effects of winter for the seed. It’s called stratification. For these seeds, you can set a test up and put the seed in your refrigerator before putting it in a warm place. The best length of the period of moist cold depends on the species. You can find this on the back of a seed packet or in any reliable gardening book.
Use the same length of time for stratification whether you are planting or doing a germination test.
Some seeds need to be slightly rubbed with a rough material before they will germinate. Thickly walled seeds like Nasturtium, Sweet Pea, and Lupine will often refuse to germinate without treatment. This process is called scarification.
It’s best accomplished by lining a small jar with sandpaper, then placing the seed in the jar with a lid. Shake for a minute and then proceeds with your germination test.
You can also nick the seed coat with a pair of nail clippers. Scarify the surface opposite the seed hilum, or point of pod attachment, where you are least likely to damage important tissue. Obviously, this method works best with large seeds that are easy to handle.
According to Southern Exposure Seed Company some seeds, like tomatoes, peppers, and certain flowers, need access to potassium nitrate (saltpeter) to germinate. This substance is naturally found in soil, but not when testing these seeds in paper towels. To overcome it, soak the towels in a solution of 2 grams of potassium nitrate, (Saltpeter) (Amazon) per quart of water. Use this same solution instead of plain water when we water these tests.
How long should your germination test last? Read your seed packet for a hint about sprouting days or find seed germination guideline tables with temp and germination days at The University of Alaska Fairbanks.
The Paper Towel Test
Duration: 3-14 days
This is the time-tested method for proofing old seed. It can take as little as three days and as long as two weeks, depending on which seed you are trying to germinate.
You will need: 10 or more seeds, paper towels or other moisture holding material, plastic zip-top bag or Mason jar, water
- Thoroughly wet the paper towel and fold it in fourths. It should not be dripping, but moist.
- Put your seeds inside the paper towel; make sure the seeds are not touching.
- Place the wet paper towel inside a plastic zip-top bag or Mason jar, to hold in moisture during the test.
- Cool weather crops should be kept between 50 and 70 degrees. Warm weather crops need to be kept between 70 and 85 degrees. Light is not necessary unless the seed packet says the plant needs light to germinate.
- Check the package every few days, make a note of sprout times, and measure germination percentages.
Sand Germination Test
Duration: Typically 7-10 days
You will need: Clean Sand, a short walled tray or container, water for spritzing the sand and keeping it wet
A sand germination test is done the same as a paper towel germination test, except that a layer of moist sand is placed over and under the seeds, and the sand it kept moist during the test. Sprouting this way useful in suppressing some fungi and may be the better option if you want to plant the germinated seeds in your garden.
Watch this video to see how.
Testing Seed Viability in Water – The Float Test
Duration 15-20 minutes
For those impatient gardener types, the water method is also the quickest.
Take your seeds and put them in a glass or jar of warm water. Let them sit for 15 to 20 minutes. Then if the seeds sink, they are still viable for planting; if they float, they most likely will not sprout.
The float test works well for large seeds the size of corn, peas, tomatoes, or peppers, but does not work if the seeds are very tiny, like carrots or lettuce. These will want to float no matter what you do, so use the water float test for larger sized seeds and use the paper towel germination method for mini size seeds.
Can you Plant Germinated Seeds?
Germination testing may require that you sacrifice a few seeds. If your seed quantity is very low or you have few seeds, skip the germination test altogether and carefully plant what you have.
If you would like to save your seedlings after the test, consider the sand test, but know that many species just can’t handle transplanting at such an early stage. Stems and roots are fragile, and a sudden change in environment can trigger shock.
If you’re determined to save the seedlings from the paper towels, leave the roots attached and cut around them on the towels, then transplant it all. Grow these indoors in a clean, loose seed starting mix until they are ready to be moved outside.
With a little planning, you can try one of these 3 reliable seed germination tests, save money and feel good about using the old seeds you have in your home.