How long does leftover grass seed last in storage?
By My Yard Editorial Team · 7/28/2026
The Quick Answer
Grass seed loses roughly 10% germination per year. Stored cool, dry, and sealed, year-old seed is fine; 3+ year old seed germinates poorly enough that you should increase the rate by 30–50% or replace it.
The Witty Breakdown
Heat and humidity kill viability far faster than time. A bag in a hot shed loses more in one summer than three winters in a basement.
Test before you commit: 20 seeds on a damp paper towel in a bag tells you everything in 10 days.
Step-by-Step Fix
- 1
Store in a sealed container in a cool, dry place, not a hot garage.
- 2
Do a paper-towel germination test before seeding with old stock.
- 3
Bump the seeding rate proportional to your test failure rate.
- 4
Note the purchase date on the bag with a marker.
Pro-Tip / Do Not Do This
Don't store seed in the garage in an open bag. Mice consider that a delivery service.
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