Depending on what part of the country you live, will depend on the longevity of the unplanted seed. If you live in a very wet, rain, humid area, with bitter winters, the seed wont last as long. The seed companies only guanrantee the seed for 1 year at the germination rate thats stamped on the bag. Thats not to say all the seed in shot at 13 months. Best to keep bag sealed as best you can, in as dry a place as possible. When you go to use the seed even if its years latter, sow it at a heavier rate than the chart.