The False Security of Seed Germination Tests

Gardeners have a reputation for being unable to toss vegetable seeds, probably because a great number of people who garden don’t just do it as an enjoyable hobby. We do it because our lives may depend on it.  As such, we can’t just throw away perfectly good seed that may be useful in an uncertain future. 

We store it carefully away until next season.  And that might get repeated once or twice, especially if the packet gets lost amongst all the other packets in the container.  We begin to wonder if that seed will even sprout and whether we should bother planting it.  And then we remember that we can perform a seed germination test. 

The seed germination test is so easy even a city slicker who has never dug a shovel into the dirt can do it.  Directions abound on the internet for how to perform this elementary test. 

Put 10 seeds on a slightly damp paper towel.  Fold or roll up the paper towel and place it in a plastic baggie.  Close the baggie, but don’t seal it entirely.  You don’t want the paper towel to dry out, but it would be nice if it could get a little air circulating.  Place the baggie in a warm place—on top of the refrigerator is ideal—and check the seeds every few days for signs of sprouting.  Bear in mind that some seeds, like peppers, can take a long time to germinate.  Count the number of seeds that germinate and multiply by 10.  That’s your germination rate. 

Keep in mind that the minimum acceptable germination rate standards vary by seed variety.  Fifty percent germination is perfectly acceptable for okra; it’s pretty low for corn.  The advice that naturally follows when people lament about a low germination rate is that you just need to plant the seeds a little thicker or closer together. 

And that might work, but it’s not necessarily true that you’ll get a harvest.  Here’s why:

As noted in the article last week on seed viability, within each seed is a dormant embryo that will become a plant, if all goes as planned.  In addition, there is the food supply that will feed the embryo while it is dormant as well as until the point it has produced the true leaves that will make its food from the sun.  How quickly that dormant embryo in the seed consumes its food supply, and the extent to which that food supply has become reduced over time is a function of the storage temperature and humidity. 

If that seed is near starvation, it may have enough food to germinate—to pass the germination test—but it may not have enough to get to the point of making true leaves that will make food from the sun and soil.  This is the case for plants that are dicots.  Dicots start out with a pair of leaves that do not look like the next leaves the plant makes, the true leaves.  The true leaf also grows from the food reserves of the seed.  The seedling may emerge from the seed, but if food reserves are inadequate, the seedling falls over and dies.  It passed the germination test but failed to grow.

So what varieties of seed are more likely to pass a germination test but still be susceptible to dying if they are too old?

Basically, almost all of the major crops are dicots.  All of these can pass a germination test but still die if they don’t have sufficient food reserves due either to age or poor storage conditions.

Legumes—beans, peas

Cucurbits—watermelon, cantaloupe, cucumber, squash, pumpkin

Nightshades—potato, tomato, pepper, eggplant

Leafy vegetables—lettuce, Swiss chard, spinach

Brassicas—cabbage, broccoli, cauliflower, rutabaga, turnip, radish

Other—beet, okra, carrots, parsnip, parsley, sweet potato

 

And what vegetable seeds are likely to be good to go if they pass the germination test?  These are the monocots, and there aren’t that many:

Corn

Onion

Leek

Garlic

Just because seeds germinate, doesn’t mean they will grow well.  Seed still needs to be fresh and stored well.  Let that corn sit in the sun for an hour, and you’re risking a much lower germination rate—even if it is super fresh.

References:

https://s3.wp.wsu.edu/uploads/sites/2061/2018/02/Growing-Vegetables-2.pdf