Very few gardeners have such large gardens that they use up all the seeds from a single packet of a particular annual, perennial, or vegetable.
Most gardening books indicate that it is possible to save seed for next year or even for several years. Consequently, it is tempting to save those extra seeds for next year.In our opinion seeds can be successfully stored for a year or more, ONLY IF conditions are absolutely correct to be sure the germination levels don't drop to 50 percent or below. Our advice is to throw away any extra seed that you can’t give to a neighbor or friend. For the saving of a few dollars you may have a lousy germination next year. It is not worth the risk to us.
However, for the obsessed out there here is what you can do to try to save some excess seed.
Seeds must be stored in a dark, cool, dry place. The best place is the freezer. Put seeds in a glass jar that also contains a dehumidifying packet of dried milk. The dried milk will absorb moisture. To make this dehumidifier, spread several layers of facial tissue and place 1 tablespoon of dried milk in the middle. Wrap up the milk and secure the packet with a rubber band. This is an effective dehumidifier for several months, but it should be replaced at least once during the winter. If the freezer is full, place the seeds in the refrigerator with the dried milk humidifier.
If you store your seeds anywhere else, such as a closet, cabinet, or basement, make sure they are kept as cool and as dry as possible. If you have any doubts about the viability of the seeds, it is best to purchase fresh seeds.