Does Grass Seed Go Bad?

Many homeowners keep a large bag of grass seed in the garage or shed to have on hand whenever a patch of bare lawn needs to be reseeded. But you may well wonder if that old grass seed is still viable, or if it has gone bad with age. If you store high-quality grass seed in ideal conditions that are dry and cool, you can count on the germination rates dropping 10% each year. Read on to learn how to tell if your grass seed is expired, tips to store it to make it last the longest, and the best way to use older grass seed. 

The Viability of Grass Seeds

Germination rates vary considerably by plant, and it also depends on how the seeds are stored. To check your specific grass variety, the germination rate is stated on the grass seed package. New grass seeds starting with an 80% germination rate—declining 10% yearly when stored in cool, dry conditions—will have a 50% germination rate after three years.

Factors Affecting Seed Viability

The viability of stored seeds of any kind are greatly influenced by storage conditions, and unfortunately, the ideal conditions for seed storage are very often exactly the opposite of how homeowners store grass seed. In general, seeds will maintain their viability longest if stored in cool, dry conditions—which is not the condition typical in most garages and sheds. The factors influencing seed viability include: 

• Seed moisture. An internal seed moisture level of 10 to 20% is ideal for most seeds. Seeds that lose moisture and fall below this level, or absorb humidity to higher levels, are likely to die.
• Storage temperature. Ideal storage temperatures for most seeds are above freezing but under 60 degrees Fahrenheit. Temperature above 100 degrees can badly affect seed viability. 
• Storage humidity. If seeds are stored in cloth sacks or open containers, their moisture levels are subject to change. In humid climates, they may absorb humidity. 

Recommendations 

There is no harm in trying to use some old grass seed for top seeding or reseeding, but you should expect there to be a lower germination rate than you would enjoy with fresh turfgrass seed. To compensate for the lower germination rate, use more grass seed than recommended to make up the difference. A box or bag of grass seed that has been stored in very warm conditions, or open to humid summer air, will not hold its viability very well. 

For the future, your new grass seed will keep best if you store it in a tightly sealed plastic bag or container so it cannot absorb moisture. You can extend its viability by keeping it out of a hot garage or shed and storing it indoors where it is cool. 

The cooler the storage temperature and the dryer the relative humidity (RH), the longer your seeds will remain viable. Seeds stored in a sealed container in a refrigerator usually enjoy the best longevity. If this isn't practical, seek out the coolest location in your home. Stored with this kind of care, your grass seed may remain viable for as long as five years.