Check the Germination Rate on the Package Label

The fastest way to know if grass seed will grow is to read the label on the bag or box. Every bag of grass seed sold in the United States must show a germination percentage — the portion of seeds expected to sprout under ideal conditions. A fresh bag typically shows 85 to 95 percent germination. If the label shows below 70 percent, the seed has aged enough that you should replace it.

The label also lists a test date, usually printed as "tested on" or "germination date." This tells you when the germination rate was measured. Seed loses viability over time, especially in heat and humidity. If the test date is more than a year old and the seed has been stored in a warm garage or shed, germination has likely dropped further since that test.

If you have lost the original bag or label, you can still run a straightforward test at home before spreading seed across your lawn.

Key Takeaways

  • A germination percentage below 70 percent on the label means the seed is too old to count on, and you should buy fresh seed.
  • Grass seed stored in a cool, dry place (below 50°F and under 40 percent humidity) stays viable for two to three years; seed in a warm garage loses viability in months.
  • A home germination test using a paper towel takes five to ten days and shows you exactly how many seeds will sprout before you spread them on your lawn.
  • Seed that has been exposed to moisture, mold, or insects should be discarded even if the label looks good.

Run a Paper Towel Germination Test at Home

If you want to know whether old seed will actually sprout, a paper towel test takes about a week and costs nothing. Wet two paper towels, wring out the excess water so they are damp but not dripping, and lay them flat on a plate. Scatter 10 to 20 seeds from your bag across one towel, fold the other towel over the top, and cover the plate loosely with plastic wrap or a plastic bag to hold in moisture.

Place the plate in a warm spot — a windowsill, kitchen counter, or shelf indoors works well. Check it every day or two and keep the towels damp (not soggy). After five to ten days, count how many seeds have sprouted a small white root. If 7 out of 10 seeds sprout, your germination rate is 70 percent. If only 2 or 3 sprout, the seed is too old to use.

This test mimics the warm, moist conditions seeds need to germinate, so it gives you a realistic picture of what will happen when you water your lawn after spreading seed.

How Storage Conditions Affect Seed Life

Grass seed lasts longest in cool, dry conditions. Seed stored in an unheated basement, garage, or shed where temperatures stay below 50°F and humidity stays below 40 percent can remain viable for two to three years. The same seed stored in a hot garage, garden shed, or outdoor storage box loses viability much faster — often within six months to a year.

Heat and moisture are the enemies of seed longevity. A garage that reaches 80°F in summer or a shed exposed to humidity from rain or watering will degrade seed quickly. If you store seed in a plastic bag or cardboard box without protection, condensation and temperature swings will shorten its life. A sealed container in a cool closet or basement is ideal.

If you bought seed last spring and stored it in a warm place all summer, assume germination has dropped significantly. A paper towel test will tell you whether it is worth using.

Signs That Seed Has Gone Bad

Beyond a low germination percentage, look for physical signs of damage. If the seed bag has been wet or shows water stains, mold, or a musty smell, discard it. Moisture causes mold to grow on seeds, and moldy seed will not sprout and may introduce disease to your soil.

Inspect the seeds themselves if you can. Grass seed should be small, hard, and uniform in color — usually tan, brown, or gray depending on the variety. If seeds are discolored, soft, or stuck together in clumps, they have absorbed moisture and are no longer viable. Insects or rodent droppings in the bag are also a sign to throw it out.

Seed that smells sour, fermented, or musty has been exposed to moisture and should not be used, regardless of what the label says.

When to Buy Fresh Seed Instead

If your germination test shows below 60 percent, or if the seed shows any signs of mold or moisture damage, buy a fresh bag. The cost of new seed is small compared to the cost of spreading dead seed across your lawn and waiting weeks to find out nothing grew.

Fresh seed is also worth buying if you are overseeding a large area or if you are seeding in fall, when you have only one window to get it right before winter. A bag with 90 percent germination will give you much better coverage and faster results than aged seed with 50 percent germination.

Check the bag label for the variety name and make sure you are buying the same type you used before, or a blend suited to your climate and sun exposure. Seed loses viability, but variety matters just as much for success.

Frequently Asked Questions

Can I use grass seed that is five years old?

Only if it has been stored in a cool, dry place and a germination test shows at least 60 percent of seeds sprouting. Most seed stored in a garage or shed for five years will have germination below 50 percent and is not worth spreading. A paper towel test takes a week and will tell you for certain.

Does the expiration date on the bag mean the seed is dead after that date?

No. The expiration date is when the seller guarantees the germination percentage on the label. After that date, germination has likely dropped, but the seed may still grow. A germination test will show you the actual rate rather than guessing.

What if I mix old seed with new seed?

Mixing works if you know the germination rate of both. If old seed is at 50 percent and new seed is at 90 percent, you are spreading a blend at roughly 70 percent germination, which is acceptable. If you do not know the old seed's rate, a paper towel test on a sample will tell you what you are working with.

Is seed that has been frozen still good?

Yes. Freezing does not harm grass seed and actually slows aging. Seed stored in a freezer or unheated garage that drops below freezing in winter will last longer than seed kept at room temperature. Thaw it slowly at room temperature before use.

How do I store seed so it lasts as long as possible?

Keep it in a sealed container in a cool, dry place — an unheated basement, garage, or closet works well. Avoid heat, sunlight, and humidity. A sealed plastic tub or glass jar in a cool corner will keep seed viable for two to three years. Label the container with the variety and purchase date so you know what you have.