Store grass seed in a cool, dry place in a tightly closed container, such as a Mason jar or plastic zipper bag. If it gets wet, it is likely to sprout in storage, making it unsuitable for later planting. If you purchased your grass seed in a paper bag, transfer the seeds into another container that will not permit humidity to enter.
Most types of turfgrass remain good and won't depreciate for about 18 to 24 months if you store it correctly. Different types of grass have different depreciation rates: For example, Kentucky bluegrass, tall fescue, annual ryegrass and perennial bluegrass can keep their viability for up to five years.
If you are unsure whether your stored grass seeds are still good, plant a few in a small pot. Count the number of seeds before you plant them, and then count the number of shoots that germinate. If the percentage is less than half, any seeding effort you undertake will be disappointing. Discard the seed, and begin with newly purchased seed for best results.
Companies that produce and sell grass seed attempt to sell it within several months of harvest. Studies have been conducted on different types of seeds and their depreciation times. Manufacturers know how long their seeds will remain good, based on the variety of grass they are selling, and they attempt to store and sell those seeds in the shortest amount of time possible. They conduct tests to determine the viability of their seeds before they send them to markets.