Leftover grass seed is common after lawn care projects, leading many homeowners to wonder if the partial bag stored in the garage is still usable the following season. Discarding viable seed is unnecessary financial and environmental waste. While grass seed viability declines over time, the rate of decline depends entirely on storage conditions. Determining if your remaining seed is still capable of germination is a straightforward process that saves time and money before your next planting effort.
How to Test Seed Viability
The most reliable method for checking the quality of old grass seed is a simple home germination test, often called the paper towel test. This process involves creating ideal conditions to see how many seeds will sprout from a small sample. Start by counting out 10 seeds, which simplifies calculating the germination rate.
Place the seeds on a damp, but not soaking, paper towel, then roll or fold the towel over the seeds. Place the bundle inside a plastic sandwich bag, leaving it slightly open so the seeds receive oxygen. Keep the bag in a warm location, around 70°F, and check it daily to ensure the paper towel remains moist.
Grass seeds typically begin to sprout within 7 to 10 days, though some varieties may take longer. After the testing period, count the number of seeds that successfully germinated. If eight out of ten seeds sprouted, the 80% germination rate is considered excellent for planting. If the rate is 50% or lower, significantly increase the seeding rate when planting to compensate for the poor quality.
Visual inspection offers a quick preliminary assessment before running a full test. Look for signs of clumping, which indicates moisture exposure, or a rancid, musty smell, suggesting mold or fungus. These conditions strongly indicate the seed has been compromised and will likely fail to germinate effectively.
Factors That Reduce Seed Lifespan
Grass seeds are dormant living organisms, and their viability is affected by environmental stressors that deplete stored energy reserves. The three primary enemies of long-term seed storage are high heat, excessive moisture, and light exposure. Exposure to high temperatures, particularly those exceeding 100°F, significantly accelerates the seed’s metabolic rate.
This increased metabolism causes the seed to burn through its stored starches and oils faster than normal, exhausting the energy needed for germination. High heat also damages cellular structures, especially when combined with high humidity. An internal seed moisture content outside the ideal 10% to 20% range can be fatal to the embryo.
If the seed absorbs too much moisture, it can prematurely initiate germination. Since the seed is not in soil, this process fails, rendering the seed non-viable. Conversely, storage in extremely dry, hot conditions can desiccate the seed, leading to irreversible cellular damage.
Maximizing Shelf Life Through Proper Storage
Properly storing leftover seed centers on the “cool, dark, and dry” principle to minimize metabolic activity and prevent moisture absorption. The ideal storage temperature is consistently below 60°F but above freezing. This temperature range keeps the seed in a deep, stable dormancy, conserving its energy until planting.
Transferring remaining seed from its original paper bag to an airtight container is highly recommended. Glass jars, sealed plastic bins, or five-gallon buckets with tight-fitting lids provide a superior barrier against external humidity and pests. Placing a small desiccant packet inside the container can help absorb any residual moisture.
The container should be stored in a location that maintains a stable, low temperature and low humidity, such as a climate-controlled basement or a cool, interior closet. Avoid placing the seed in areas with large temperature swings, like an outdoor shed, attic, or a garage exposed to direct sun. Storing the container off the floor also prevents potential dampness from concrete surfaces.
Alternative Uses for Non-Viable Seed
If grass seed fails the germination test or the viability rate is too low for a uniform lawn, it can still be repurposed.
Overseeding and Patching
For seed that shows a low but measurable germination rate, use it for overseeding or patching small, bare spots. To compensate for the loss of viability, increase the seeding rate by about 10% for every year the seed has been stored.
Soil Amendment
Non-viable seed can be safely incorporated into a compost pile or mixed into topsoil as organic matter. The seed material will break down, adding carbon and bulk to the soil mixture. This is a beneficial disposal method, provided the seed is uncoated and free of any chemical treatments or fungicides.
Animal Feed Filler
Another alternative is to use the seed as a filler in bird seed mixes or chicken feed. It is important to verify that the grass seed is natural and has not been treated with any chemical coatings, colorants, or fungicides, as these additives can be harmful to animals. If the seed is pure and untreated, it provides a safe, economical source of added bulk for wild bird feeders.