When a bag of grass seed has been sitting unused, the primary concern is its viability, which is the seed’s capacity to sprout and grow. Like any dormant organism, grass seed gradually loses this ability over time, even under good conditions. Planting non-viable seed results in wasted time and effort, leading to patchy, thin results rather than a dense lawn. Checking the current state of old seed is a necessary first step to ensure planting efforts will be successful.
Quick Visual and Olfactory Assessment
Before attempting any tests, a simple visual and olfactory check can determine if the seed is compromised. Pour a handful of seed onto a clean surface to inspect it closely. Look for signs of mold, which often appears as white, gray, or greenish fuzz, or any evidence of mildew. These growths indicate the seed has been exposed to excessive moisture, which can destroy the embryo inside.
Inspect the seeds for clumping or a sticky texture, which suggests moisture absorption and viability decline. Healthy seeds should be dry, uniform in color, and feel firm to the touch. Small holes or dust-like material may signal insect activity that has consumed the internal contents. A musty, sour, or fermented scent is a clear indication the seed has degraded and should be discarded.
The DIY Germination Test
The most definitive way to assess the planting potential of older grass seed is by conducting a simple at-home germination test. This procedure creates the ideal environment for sprouting and reveals the percentage of viable seeds. Select a representative sample of 10 or 20 seeds, ensuring you do not pick only the best-looking ones, as this would skew the results.
Moisten a paper towel until it is damp but not dripping wet, then spread the selected seeds out on one half of the towel. Fold the other half over the seeds so they are sandwiched between the damp layers. Place the folded towel into a sealed container, such as a zip-top bag, to retain moisture.
Place the container in a consistently warm location, such as on top of a refrigerator, and check it daily to ensure the paper towel remains moist. Most grass seeds will begin to sprout within five to ten days, though the exact time varies by species. After the appropriate time has passed, gently unroll the towel and count the number of seeds that have successfully sprouted, showing a root and a shoot.
Calculate the estimated germination rate by dividing the number of sprouted seeds by the total tested, and multiplying by 100. For example, if you tested 20 seeds and 14 sprouted, the viability is 70%. While fresh seed typically boasts a germination rate of 80% to 90%, a rate above 50% means the seed is usable. If the rate is low (50% to 70%), compensate by increasing the amount of seed spread over the planting area.
How Storage Conditions Affect Longevity
The lifespan of grass seed is controlled by the environmental conditions during storage, primarily temperature, humidity, and light exposure. Grass seed is a living product that slowly respires, consuming stored energy, a process that accelerates with heat. Storing seed where the temperature frequently exceeds 80 degrees Fahrenheit can quickly degrade viability, sometimes halving the lifespan for every 10-degree increase.
Moisture is a significant factor; when seed absorbs humidity, its internal moisture content rises, speeding up metabolic processes and increasing the risk of mold growth. The ideal storage environment is cool, dry, and dark, with temperatures kept between 40 and 60 degrees Fahrenheit. Sealing the seed in an airtight container helps maintain a low moisture level and prevents humidity fluctuations.
Under these optimal conditions, most quality grass seed remains viable for one to three years, with a gradual decline of approximately 10% per year. Seed stored in a hot, humid garage or shed may lose most of its viability in less than a year. Protecting the seed from light is also important, as light can trigger a premature end to the seed’s natural dormancy.