Seed viability refers to a seed’s capacity to germinate and grow into a healthy, productive plant under suitable conditions. This potential determines the success of any planting effort, making viability testing a practical step for gardeners. Testing older seed packets saves time and resources that would be wasted on non-sprouting seeds. Understanding the likelihood of a seed sprouting allows for an informed decision about whether to plant the existing supply or purchase new stock.
Quick Assessment: The Float Test
The water float test provides a quick, preliminary screen for larger seeds like beans, peas, or corn. This method relies on the principle that non-viable seeds often lose internal mass as their food reserves degrade, causing them to float. A seed that is hollow or very dry will have a lower density than water.
To perform this test, place the seeds in a container of water and wait for about 15 minutes. Seeds that sink suggest a dense internal structure and are more likely to be viable, while those that float are often discarded. This is not a definitive test for all varieties, as some viable seeds may float, so it is best used only as a rapid initial screening tool.
The Standard At-Home Germination Test
The most accurate way to assess a seed batch’s potential is by conducting a controlled germination test, often called the “paper towel test.” This method simulates ideal growing conditions and directly measures the percentage of seeds that are metabolically active and capable of sprouting. Select a representative sample of seeds from the packet; a minimum of 10 or 20 is recommended for home testing, as this simplifies the final calculation.
Begin by moistening a paper towel, coffee filter, or blotter paper until it is damp but not dripping wet. Spread the counted seeds evenly on one half of the damp material, then fold the other half over them or roll it up like a jelly roll. Place the rolled or folded paper towel inside a plastic bag or a covered container to maintain high humidity. Label the container with the seed type and the date the test was started.
Place the sealed container in a warm environment, ideally maintaining a temperature between 68 and 77 degrees Fahrenheit. This range is suitable for many common vegetable and flower seeds; a spot on top of a refrigerator often provides this gentle warmth. Check the seeds every couple of days to ensure the paper towel remains moist and to monitor for initial signs of growth.
Successful germination is confirmed by the emergence of a small root, known as the radicle, which indicates the embryo is alive. The time required varies significantly; some seeds sprout in a few days, while others may take a week or more. The test is complete once the expected germination period has passed, or when no new sprouts have appeared for a few days.
Interpreting Viability Rates
After the test period, carefully unroll the paper towel and count the number of seeds that have successfully sprouted. To determine the germination rate, divide the number of germinated seeds by the total number tested, then multiply by 100 to get a percentage. For instance, if you tested 10 seeds and 7 sprouted, the viability rate is 70%.
A viability rate above 80% is considered excellent for most vegetable seeds, allowing you to sow them at the normal recommended density. If the rate falls between 50% and 80%, the seeds are usable, but increase the planting density to compensate for lower expected germination. If the test reveals a rate below 50%, the seed lot is poor quality, and it is usually more efficient to purchase a fresh packet. This percentage allows gardeners to accurately adjust their sowing quantity.