Two men are walking on a treadmill at a leisurely pace. Both men are using little energy to keep up with the machine, and look refreshed. Which man is in better athletic condition?

The answer is….there’s no real way to tell at the pace they are going.

Speed up the treadmill and place some stress on the athletes, and you should quickly see which man holds up to the stress and is in better shape.

You can say the same for seed. Under ideal conditions in the lab, with little or no stress, you may not be able to see which seed lot is actually the strongest. Comparing different seed lots under stress conditions, like cool or hot or minimal moisture, or even too much moisture will quickly separate the strongest seed lots from the weaker seed lots. And by measuring the speed at which the seed germinates under the stress conditions, you can get an even clearer picture of the strongest or most vigorous seed lots.

You get the most vigor information when comparing seed lots under a stress that makes germination difficult, but doesn’t kill the seed. Here are a couple of tests that use stress to separate the weak from the strong.

Accelerated Aging

Seeds are placed into a high humidity, high temperature box for several days, stressing the seeds before the actual germination test. After the aging treatment, the seeds are planted to see which lot held up the best against the damaging storage conditions.

Cold tests

Seeds are planted and placed into a cold environment for several days and then moved into a warmer condition. Germination characteristics are measured to see how the seed held up against the cold stress treatment.

Here’s a common test that relies mainly on speed of growth to determine seed lot strength. The fastest germinating and growing seed lot is said to be the most vigorous.

Slant Test

Seed is placed on wet blotter paper in a box. The box is set up at a slant so roots will grow straight down toward the bottom of the box. Root length is measured. The seed with the fastest growing root, is the seed with the most vigor.