Gardeners often wonder if forgotten packets of seeds from a previous season are still viable. Viability is the ability of a seed to sprout and produce a healthy plant. Seeds do not suddenly expire; instead, their viability slowly decreases over time, making successful germination less likely. Whether last year’s seeds are worth planting depends on how they were stored and the specific variety’s natural lifespan.
Factors That Determine Seed Lifespan
High temperature and high moisture are the two greatest enemies of stored seeds, as they accelerate metabolic processes. Every seed holds a finite amount of stored energy. Exposure to warmth and dampness causes the seed to respire faster, burning through the internal food reserves needed for germination. This loss of internal energy reserves is the primary cause of viability decline over time.
The moisture content within the seed is the most significant factor influencing its longevity. If moisture content is too high, the seed becomes susceptible to mold and fungal growth, which rapidly destroys the embryo. Conversely, overly dry conditions can cause physical damage or induce hard-seededness, making germination difficult. Since higher temperatures increase the adverse effects of moisture, a cool, dry environment is always preferable for long-term storage.
Categorizing Seed Longevity by Type
Different plant families have varying natural longevities, even when stored under optimal conditions. Seeds are broadly grouped based on their inherent shelf life, providing a general guide for gardeners. Short-lived seeds should ideally be replaced every one to two years. These include members of the onion family (chives and leeks), parsnips, and corn. These varieties lose viability quickly and should be prioritized for testing or fresh purchase.
Seeds with a medium lifespan typically remain highly viable for three to four years after packaging. This group includes common garden vegetables like beans, carrots, peppers, and peas. A slight decrease in germination rate is expected each year, making it wise to sow them a little more densely as they age. Long-lived seeds are the most resilient, often maintaining strong viability for five years or more. Examples include tomatoes, cucumbers, squash, and many brassicas like cabbage and broccoli.
How to Test for Seed Viability
The paper towel or “ragdoll” method is a simple home test that can accurately determine the germination rate of older seeds before planting. Select a sample of at least ten seeds from the packet to ensure the test is representative. Lightly moisten a paper towel until it is damp but not soaking wet, which prevents fungal growth while providing necessary hydration.
Space the ten seeds on one half of the damp towel, then fold the other half over them to create a seed sandwich. Place the folded towel inside a plastic bag or container, leaving it slightly open for air circulation. Put the setup in a warm, dark location, such as the top of a refrigerator, and check daily to ensure the towel remains moist. After the expected germination period, count the number of sprouted seeds. If seven out of ten seeds sprout, the germination rate is 70 percent, meaning the remaining seeds are generally acceptable to use, though they should be planted more thickly than usual to compensate for the anticipated lower yield.
Improving Seed Storage for Next Season
To maximize seed longevity, gardeners should focus on maintaining a consistently cool, dark, and dry environment. The goal is to minimize the metabolic activity within the seed that leads to deterioration. A common strategy is storing seeds in an airtight container, such as a glass jar or metal tin, which prevents the exchange of moisture with the surrounding air.
To actively reduce the moisture inside the container, a desiccant material can be included before sealing the lid. Powdered milk or a small packet of silica gel will absorb any residual humidity trapped within the container. Storing these sealed containers in a stable, cool place, like a dedicated mini-fridge or a basement, further slows the aging process, helping to preserve the seeds for multiple years.