Does Grass Seed Go Bad?

Reseeding your lawn always ends up with half a bag of unused grass seed. What can you do with leftover grass seed? Will it go bad? Can you still use it next year?

Grass seed can go bad if it’s not properly stored in a dry, cool, and dark place. When grass seed is kept in a humid and warm place, it’s vulnerable to mold, rot, and germinating early. Properly stored in a dry, cool, and dark place, grass seed will last up to ten years, although the germination rate will decrease approximately 10% each year after harvest.

Does Grass Seed Have an Expiry Date?

Grass seed does not have an “expiry date”, per se, but the germination rate (the percentage of seeds that will grow) decreases each year.. For example, if in Year 1, 10 seeds germinated, Year 2 might be 8 – 9 seeds, Year 3 might be 6 – 7 seeds, and so on. The initial germination rate (80% or above for quality seed) and the date tested will be printed on the package. Grass seed can last up to 10 years when stored properly.

How To Properly Store Grass Seed

The key to properly storing grass seed (or any kind of seed) is to avoid mimicking the seed’s ideal growing conditions:

  1. Keep dry and avoid moisture and humidity. Excess moisture increases the likelihood of fungus, mold, and premature sprouting. Store your seed in a cool, dark, and dry space. A cool place is better than a warm place, but a dry place is most important. You have a few options for this:
    1. A plastic container, or better yet a glass one, stored in a dry area will prevent moisture from reaching the seeds.
    2. If you need to store the seed in bulk storage bags, then try to place in an area with airflow to counteract the humidity that can seep through the bag.
    3. Place an opened box of baking soda in the area to lower moisture levels.
  2. Store away from rodents and other pests. It’s tempting to just leave the plastic seed bag in the garage’s corner, but it’s an easy target for mice. If rodents get into the bag, they can eat the seed but leave the husk, which can look like a whole seed to the untrained eye. Rodents can chew through plastic containers, but they can’t get through glass ones.
  3. Date and label leftover seeds. This happens to every gardener. You store away the seeds without labelling, believing that you’ll remember what they are and what year you got them. Then come next spring, you’re staring at seeds wondering when the heck you got these. You can avoid this trouble by labelling the container with the harvest date and seed variety.

The best places to store seed include:

  • Air-tight containers in the basement. A basement is a humid place, but storing seed in air-tight containers will keep seed dry. Glass jars are your best bet. If you have too much seed left, then choose somewhere else to store it.
  • Main-floor closet. This is your best bet for seed storage, as the main floor will have better ventilation than a basement. It’ll be warmer, but dry is more important than cold.
  • Unheated garage or shed. If your seed is completely dry, you can put them in an air-tight container in your unheated garage or shed. Rodents can chew through plastic, so use glass if you can. Seeds will endure freezing temperatures.

Avoid storing seed in:

  • In the basement, unless in air-tight containers. Basements are humid, and even when they’re finished, they don’t have the same ventilation as other places in your house. Avoid root cellars, as they’re designed to keep humidity levels at 80-95%.
  • In the fridge or freezer. Fridges may be cold, but they are too humid for grass seed storage. Dry is more important than cold.
  • In a heated garage. Whenever you open a door in the winter, you let in cold air, which leaves condensation on surfaces and raises the humidity.

Before using stored grass seed, always check for mold and mildew on the seeds. Even the best laid storage plans aren’t foolproof.

How Do You Know If Grass Seed is Still Good?

To find out if grass seed is still good, do a germination test. (It’s super easy.)

You will need:

  • A sealed plastic bag
  • A paper towel
  • A hand mister/spray bottle
  • 10 seeds

To test germination rates:

  1. Dampen the paper towel with the spray bottle spritz by spritz, waiting in between to see how far the current water soaks through. Use just enough water that the capillary action dampens the edges of the towel. If there’s too much water, the seeds will rot.
  2. Put the damp paper towel inside the plastic bag.
  3. Place 10 seeds on top of the paper towel.
  4. Seal the plastic bag.
  5. Set the plastic bag in a warm place for 10 days.
  6. Watch for germination. The number of seeds that germinate out of the 10 is your germination rate. (So if 5 seeds germinate, then the germination rate is 50%.)
  7. Apply grass seed according to the germination rate. For example, if it’s 50%, apply twice as much as recommended.

Does Grass Seed Go Bad If Frozen?

Grass seed will not go bad if it freezes, so long as the grass seed is dormant and dry. If the seeds aren’t completely dry when frozen, then the moisture inside the seeds will freeze and damage the seeds.

Annual grass seed goes to seed in the autumn, lie on the soil throughout the winter, and germinate in the spring. Dormant seeding takes advantage of this process by sowing grass seed in the late fall or early winter to germinate once spring arrives, but it’s risky. If temperatures temporarily warm up mid-winter and the seed has access to moisture, it will germinate. Freezing temperatures kill off germinating seeds.

Freezers and refrigerators are too humid for storing seed.

Can Grass Seed Be Stored Below Freezing?

Grass seed can be stored below freezing, but it’s riskier than storing it in a place between 32F (0C) and 60F (15C). Fridges and freezers are too humid for seed storage. An unheated garage or shed is better if it’s dry, but the grass seed must be completely dried out to avoid freezing temperatures damaging the seed.

It’s better to store seeds in a dry place than a cold one.

Will Grass Seed Grow After it Freezes?

If the grass seed was completely dry and dormant when it froze, then it should still be able to grow. A germination test will quickly tell you whether this is the case.

Final Thoughts

With some preparation, grass seed can last several years with high germination rates. You’ll save money in the long run by not having to buy more for touchups.



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