Seed viability refers to the ability of a seed to germinate and grow into a healthy plant, a property that naturally declines over time, even with proper storage. Testing the viability of stored seeds is a simple, proactive step that saves significant time and effort in the garden. Utilizing a small sample determines the potential of an entire batch, helping you avoid the frustration of planting non-viable seeds and waiting for sprouts that will never appear. This preventative measure ensures a successful planting season.
Physical Signs of Deterioration
A gardener’s first check for seed quality involves a quick, non-destructive sensory evaluation before any water is introduced. Visually inspect the seeds for any signs of mold, which often appears as a fuzzy or dusty growth, indicating high moisture exposure during storage. Look closely for discoloration that deviates from the seed’s normal hue, like a darkening or a pale, bleached appearance, which can suggest degradation or poor handling.
Seeds that are shriveled, cracked, or excessively wrinkled may have been improperly dried or suffered mechanical damage, compromising the protective seed coat and internal embryo. Check for tiny holes or tunnels that reveal pest infestation, which means the internal food reserves have been consumed. A strong, rancid, or musty smell upon opening a storage container is a clear indicator of lipid degradation or fungal contamination, suggesting the batch is no longer viable.
The Simple Float Test
The float test is a quick preliminary measure based on the density of the seed’s interior tissue. Seeds with a plump, healthy embryo and intact food reserves are typically dense and will sink when placed in water. Seeds that are hollow, damaged, or degraded will lack this density and remain floating on the surface.
To perform the test, drop a small sample of seeds into water and wait for about 15 minutes. While sinking seeds are generally considered viable, the test is not definitive for all species. Some healthy seeds may float due to trapped air, and some non-viable seeds may still sink, meaning the float test serves only as a screening tool.
Conducting a Viability Test
The most reliable method for determining a seed lot’s potential is a germination test, which mimics ideal planting conditions to force the seeds into growth. This test, commonly performed using the paper towel method, requires counting a small, representative sample, such as 10 to 20 seeds, from the batch. Lightly dampen a paper towel so it is moist but not dripping, and space the counted seeds evenly on one half of the towel.
Fold the other half over the seeds, creating a moist “sandwich,” and place the entire packet into a sealed plastic bag or container to maintain humidity. Place the container in a warm location, typically between 68 and 77 degrees Fahrenheit, which promotes germination in most common vegetable and flower seeds. Check the seeds every few days, spritzing the towel lightly if it begins to dry out, and look for the emergence of a root or shoot, which confirms viability.
Allow the test to run for the average germination period of the specific seed variety, which can range from a few days to two weeks. Once the test is complete, count the number of seeds that have successfully sprouted to calculate the germination rate. The formula for this calculation is: divide the number of sprouted seeds by the total number of seeds tested, and multiply the result by 100 to get a percentage. This percentage provides a highly accurate prediction of how the entire seed batch will perform when planted.
Planting Strategies for Older Seeds
The calculated germination rate provides actionable data to guide your planting decisions for the remainder of the seed batch. If the test reveals a high viability rate (80% or greater), plant the seeds at the normal density recommended on the packet. A moderate rate (50% to 75%) indicates that you should sow more seeds per planting hole to compensate for expected failures.
For example, if seeds show a 50% viability rate, plant two seeds for every one plant desired. If the germination rate falls below 30% to 40%, the seeds have insufficient vigor and should be discarded. Adjusting the planting density based on test results ensures you achieve your target number of seedlings.