Seed viability testing, often called a germination test, determines the percentage of seeds in a batch capable of sprouting. This process is particularly useful for assessing older seed stock or seeds stored under less-than-ideal conditions. Confirming seed quality before sowing saves the home gardener time and resources by avoiding the frustration of empty garden rows.
Selecting a Sample and Gathering Materials
Before beginning the test, it is important to select a representative cross-section of the seeds from the entire packet or container. For a small-scale home test, a sample size of 10 to 20 seeds is typically sufficient to provide a statistically relevant result for the overall batch. It is important to randomly pick seeds without culling any that appear damaged or discolored, as this would bias the final germination rate.
The materials required are easily found in most homes, making the test highly accessible. You will need a few paper towels or coffee filters, a sealable plastic bag, a plant mister or small cup of water, and a permanent marker for labeling. The paper towel or filter will serve as the germination medium, providing the necessary moisture and oxygen for the seeds to sprout.
Accessible Germination Testing Methods
The most common method for testing seed viability is the Paper Towel/Plastic Bag Test. To start, lightly moisten a single paper towel with water until it is damp but not dripping wet; excessive water can promote rot. Lay the towel flat and evenly space the chosen sample of seeds across one half of the paper, ensuring they are not touching.
Carefully fold the other half of the paper towel over the seeds, creating a moist, dark environment. Slide the folded towel into a clear plastic zipper-top bag, which maintains high humidity. Leave the bag slightly open or unsealed to allow for air circulation, which prevents mold buildup and ensures the seeds receive oxygen.
Place the bag in a warm location, such as on a heat mat or refrigerator top, ideally between 70–85°F (21–29°C). Check the bag every couple of days to ensure the paper towel remains moist, misting it lightly if needed. Germination time varies by species, ranging from a few days to up to two weeks, at which point the test is concluded.
Soil/Tray Test
A secondary method is the Soil/Tray Test, which evaluates seeds under actual planting conditions. This involves sowing a small, counted sample of seeds into a tray of sterile potting mix at the correct depth. While this method provides a better prediction of field emergence, it requires more space and more closely monitored conditions than the paper towel method.
Calculating and Applying Germination Rate
Once the specified germination period has passed, the test is complete, and it is time to count the successful seeds. A seed is considered successfully germinated when it has developed a visible root, called the radicle, which is often accompanied by the emergence of the shoot. Disregard any seeds that have rotted or show only stunted, weak growth.
To determine the final germination rate, use a simple percentage calculation: divide the number of successfully germinated seeds by the total number tested, then multiply the result by 100. For example, if 16 out of 20 tested seeds sprouted, the calculation (16 / 20) x 100 results in an 80% germination rate.
A germination rate of 80% or higher is considered excellent and means the seeds can be sown normally in the garden. If the test reveals a lower percentage, such as 50%, the gardener must adjust their planting strategy to compensate for the weaker batch. To achieve the desired number of plants, one would need to sow twice as many seeds as originally planned to account for those expected not to sprout.