Seed Germination Testing

Not sure if you can plant last year’s seed this coming season? The best way to find out is by doing a simple germination test. The test should be done in the winter, before purchasing your new seed. You can also use this method to pre-germinate seeds that are difficult to get started in the garden.

Materials:
• a few sheets of paper towels
• small plastic bag
• water
• seeds to test, 5-10 of each variety. I have plenty of each, so I’m using 10. The bean seeds will be discarded after the test as it would be a challenge to grow them indoors until their late May planting time.

For this article I’m testing three varieties of vegetable seed:
• Edamame soy bean ‘BeSweet’: Last summer I left some pods to dry on the plants so I’d have seed for this year. Some were still drying when the plants were killed by an early frost 9/21/2020. I don’t know if the seeds collected post-frost were completely mature. Also, some of the seeds have visible damage from stink bug feeding. Will they grow?
• Kale ‘All Star Mix’: I harvested this seed the summer of 2019 from plants that had overwintered from my 2018 garden. Commercially this would be considered 1 years old seed and it should be fine.
• Pole bean ‘Monte Cristo’: purchased for the 2019 season. Germinated well in 2019 and 2020, but beans have 3 year viability and my storage is not particularly good so I’ll test it.
Procedure:
• Write the seed name on a paper towel with a ball point pen or pencil. Record the seed count and the date the test started.
• Select seeds to test. I’m testing the smaller or more damaged seeds as they are less likely to grow so provide a tougher test, plus I want to save the bigger/better seeds for the garden.
• Moisten the paper towel with tap water. It should be damp, not soggy. Big seeds will require more water than tiny seeds.
• Place the seeds on the paper towel and roll or fold.
• Place the towels in a plastic bag. Close loosely. Place in a warm spot, where you won’t forget it.
• Check for germination after 2 days and every day thereafter. If the paper towel has dried, spritz on a bit more water.
• Stop testing after 7 days. Count the number of seeds that sprouted then divide by the number tested. This gives the germination percentage.
• Decide if the germination rate is acceptable. I’d use anything with a rate of 80% or higher. If the rate is less than 50% I’d get new seed. Between 50%-80% I’d probably sow more thickly then thin out or move overcrowded plants.

Test preparation. towels are labeled, seeds counted out and spritzed with water.

Test preparation: seeds are rolled up in the towels and ready to go into the baggie.

Day 2, first check: all 10 kale seeds sprouted for a 100% germination rate.

Day 2 first check on the beans.The Monte Cristo bean seeds from 2019 are absorbing water slowly. The soy bean seeds are absorbing water much more quickly, probably because the seed is newer. The stink bug feeding damage on the soy has turned into depressed black spots on the seeds. The paper towels containing the beans are a bit dry so I spritzed on more water.

Day 4: All 10 of the Monte Cristo seeds have sprouted for a 100% germination rate. I will plant from the packet in May. Seven of 10 soy beans sprouted and the other three might sprout soon. Even though the germination rate is 70% I would not plant these seeds unless I had no alternative. The stink-bug feeding damage is causing the plants to start slower and weaker than a plant from undamaged seed.

Using Old Vegetable Seeds

Got leftover seeds?

Often a seed packet contains far more seeds than is needed for a single garden season. Don’t throw out those leftovers! You may be able to use them the following year.

Spring of 2020 seed was difficult to buy. Increased demand caused retail stores to sell out by early May. Reduced staffing and Covid distancing requirements caused online vendors to focus on farm orders. Orders from individual gardeners placed after April 1, 2020 were often delayed until late May.

I just checked the web sites of three online seed vendors for a couple vegetables customarily direct sown. All were “Out of stock” for some varieties of pole bean and carrot seed. In times like these, you should consider using using last year’s seed leftovers. Will that work?

A viable seed is one that is capable of growing under suitable conditions. Factors affecting seed viability include the seed’s age and the temperature and humidity during storage.

Some seed, particularly onion, parsley, and parsnip seed, are notoriously short lived even if stored in the best of conditions. Their seed should be planted within one year. Once, as a test, I planted 3 varieties of the previous year’s onion seed. About half of one variety germinated, and only a couple seeds of the other onion varieties grew.

Other seeds are viable for extended periods. This list is taken from: https://hortnews.extension.iastate.edu/1999/4-2-1999/veggielife.html

Approximate life expectancy of vegetable seeds stored under favorable conditions:
• 1 year: onion, parsley, parsnip and salsify
• 2 years: sweet corn, leek, okra and pepper
• 3 years: bean, broccoli, carrot, celeriac, celery, Chinese cabbage, kohlrabi, peas, spinach
• 4 years: beets, Brussels sprouts, cabbage, cauliflower, Swiss chard, eggplant, kale, mustard, pumpkin, squash, tomato, turnip, and watermelon
• >4 years: collards, cucumber, endive, lettuce, muskmelon, radish and basil

For longer seed viability seeds should be stored in a cool, dry location. Ideal storage is less than 40° F. with a relative humidity less than 20%. Placing the seeds in a sealed jar in the refrigerator or freezer, possibly including some desiccant, could extend seed lifetime beyond what is shown in the table.

What if you store your seed as I do? Many years I’ve left my seed box on a table in the living room, where the summer temperature can reach 85° F and the humidity hits 85% (no AC). In this case, subtract a year from the expected seed life-time. Typically I will plant a packet of carrot seed for two years, though I’ve used the same packets of Chinese cabbage and celeriac for 4 years. Last year I got careful and moved my seed box to the basement where the temperature never gets above 75° F and a dehumidifier keeps the relative humidity around 50%.

When you plant your seed, take note of the germination rate. Lets say you planted your peas with seeds 2” apart in the row. If there are gaps in the row of sprouted plants, figure out what portion of your seeds did not sprout and write it on your seed packet. Mediocre germination this year means the remaining seed should not be saved for next year.

Still nervous about planting last year’s seeds? Perform a seed germination test, explained in the next post.

For more information see:
https://www.motherearthnews.com/organic-gardening/viability-of-seeds-zmaz00onzgoe
It is tougher to find viability information for flowers, but a web search for ‘flower seed viability’ will yield results.