A viable seed contains a living embryo capable of germinating and developing into a healthy plant under favorable conditions. A seed is non-viable if it is dead, too damaged, or too old to sprout. Using non-viable seeds wastes valuable time and resources, delaying the growing season unnecessarily. Growers who use saved seeds or older packets benefit from testing their supply before planting.
Initial Assessment Through Visual and Physical Cues
The first step in evaluating seed quality is a non-destructive physical examination for immediate signs of decay or pest infestation. Look closely for mold or fungus, which appears as a fuzzy growth and indicates excessive moisture during storage. Seeds should exhibit a uniform color typical for their variety; discoloration, such as dark spots or a chalky appearance, suggests degradation.
Inspect the seeds for physical damage, such as tiny pinholes or chew marks, evidence of insect pests. Perform a simple “smell test,” as a rancid or sour odor indicates that the seed’s internal oils have degraded or that bacterial/fungal rot is present. A good seed should feel firm and solid to the touch, not brittle, dusty, or hollow, which suggests the loss of internal food reserves.
Practical Viability Testing Methods
For a more definitive assessment, specific testing methods measure the percentage of seeds that are still alive and capable of sprouting. The Water Float Test is the quickest method, though it is not entirely conclusive, and works best for larger seeds such as beans, peas, or corn. Place a sample of seeds into a glass of water for about 15 to 20 minutes; seeds that sink are typically denser, indicating a solid, intact embryo and a higher likelihood of viability. Seeds that float often contain a hollow interior due to age or damage, though floating is not always a definitive bad sign.
The Paper Towel Germination Test, sometimes called the Ragdoll Test, is the most reliable method for determining viability. To perform this, count out 10 seeds so that the resulting math easily yields a germination percentage. Place the seeds onto a paper towel that has been moistened until damp but not dripping, ensuring the seeds are not touching one another. Roll the towel loosely, place it inside a sealed plastic bag or container to maintain humidity, and keep it in a warm environment, ideally around 70°F.
After 7 to 10 days, carefully unroll the towel and count the number of seeds that have sprouted a root (radicle). If the test reveals a germination rate below 70%, the remaining seeds should be planted much thicker to compensate for anticipated failures or replaced entirely. For very large seeds, a destructive Cut Test can be performed by slicing the seed open to visually confirm the presence of a firm, white, healthy embryo and endosperm.
Understanding Seed Lifespan and Storage Impact
A seed’s ability to germinate declines over time because the living embryo inside slowly consumes its stored energy reserves through respiration. This aging process is accelerated by poor environmental conditions: excessive moisture, high temperature, and light exposure. Moisture is particularly detrimental because it can trigger premature germination or encourage mold growth. The general rule for maximizing longevity is to store seeds in a cool, dark, and dry environment, as every 10°F increase in storage temperature can significantly reduce a seed’s shelf life.
Optimal storage involves maintaining temperatures below 50°F and keeping the relative humidity below 20%. This is often achieved by storing seeds in hermetically sealed containers, like glass jars, sometimes with a desiccant packet. Longevity varies widely by species; onion and parsnip seeds typically retain viability for only about one year. Conversely, tomato and pepper seeds can remain viable for four years or more under the same conditions.