Does Grass Seed Go Bad? What You Need to Know About Planting Old Seeds

When you're going through your spring lawn care checklist, reseeding and repairing those thin, bare, or brown patches will probably be at the top of the list. After all, everyone wants their lawn to look its best for summer barbecues or garden parties. But does grass seed go bad? 

If you’ve found a big box of grass seed tucked away at the back of your garage, there’s no sense in letting it go to waste, right? Well, that’s complicated. The crop quality, growing conditions, species, and storage environment all play a part in how long grass seed lasts. Learn when grass seed goes bad and how to tell below. 

How Long Does Grass Seed Last Before It Goes Bad?

If you’re planning to revitalize your lawn this season, you should opt for fresh, high-quality seed varieties to give yourself the best chance of having a lush, green yard. Viability drops the longer seeds linger, meaning you’ll have to plant more grass seed to cover those bald patches after a while, and your lawn might not be as robust.

But with the right storage, grass seed life spans can range from 18 months to over five years, depending on the species you select and whether or not the pack is open. 

• Properly stored unopened grass seed can last up to five years. 

• Properly stored open grass seed can last up to 18 months.

You’ll usually see a germination test date and germination rate on a box of store-bought grass seeds. Germination rates are typically over 80% when new, and if you store your grass carefully and use it within 18 months of purchase, this should be pretty spot on. 

How to Know if Grass Seed Went Bad

Can grass seed go bad? The short answer is yes. If you spot excess moisture, mildew, or fungi, toss the seed. But, if you’re not sure, test the grass seed before you get rid of it. 

Here’s how to tell if your grass seed is bad: 

1. Moisten a paper towel and lay it on a clean countertop.

2. Place 10 grass seeds on the paper towel, well-spaced in a row.

3. Fold or roll up the paper towel.

4. Put the damp, rolled paper towel in a ziplock bag.

5. Leave the bag somewhere warm for 7–10 days.

6. Remove the towel from the bag and count the germinated seeds.

For example, if nine seeds germinate, you have a 90% success rate. If only five seeds sprout, you have a 50% success rate. 

Even if the germination rate is 50% or less, you can compensate by sprinkling more seeds. You might want to keep older grass seeds for overseeding projects where it’s not a disaster if some seeds don’t sprout.

Will Expired Grass Seeds Still Germinate?

Just because your box of seeds has passed its expiration date doesn’t mean you have to toss it. Unless you’ve been keeping it in a soggy spot for years, it’s still worth giving it a whirl. 

Germination rates drop 10% to 20% per year. So, you might want to do a quick germination rate test after a couple of years. But if you’d rather not deal with testing the germination rate of your seeds, a local lawn seeding company can get your yard in shape for you. 

How to Store Grass Seed to Make It Last Longer

Humidity, vermin, storage weevils, sunlight, and extreme temperature fluctuations can affect how long grass seed lasts before it goes bad. By storing your seeds properly, you can save on the overall cost to seed a lawn or reseed it down the road. 

If you need to store grass seeds, keep these tips in mind to increase their life span:

• Store the grass seed in a sealed, rigid, air-tight container.

• Label the container with the date you opened it or purchased it.

• Pop desiccant packs inside the container before sealing to keep moisture at bay.

• Keep the seeds in a consistently dark, dry, cool spot.

• Store seeds at their ideal temperature, usually around 40 to 50 degrees Fahrenheit.

• Steer clear of unheated sheds or garages.

• Keep the container off the floor.

• Ensure there’s ample airflow around the storage container.

Choose a Longer-Lasting Grass Species

The type of grass you select for your yard affects how long the seeds will last. According to Oregon State University, studies show that 50% of seeds from Kentucky bluegrass, perennial ryegrass, and tall fescue can germinate after three to five years of storage. Creeping bentgrass can germinate at a 50% rate after five years. 

In comparison, orchardgrass seeds may only offer these germination rates after one to two years of storage.

Select Superior Grass Seeds for a Longer Life Span

Environmental conditions and production techniques can affect crop quality and grass seed life spans. Pick a superior seed stored in boxes (rather than bags) from a reputable supplier. A bonus is finding a manufacturer that seals their seeds right after harvesting and before transport. Buying an unlabeled bag off the clearance rack isn’t a recipe for success. 

If you need help selecting the right grass seeds for your lawn, contact a lawn care company near you. 

Gemma Johnstone contributed to this piece.