I just keep them in air tight packages in room temperature and they are fine for 3-5 years (maybe longer but I never have enough left over to try). The older they are the fewer germinate but most are still viable.
That date on the package is the date they were packed, not an expiration date. I definitely would not store them in the freezer. If you could store them in a freezer, you could also plant them in the fall, and they would come up in the spring despite the fact that the ground froze; but with very few exceptions, they don't.
Just avoid temperature extremes, and they will be fine. I put mine in freezer bags and try to get out as much air as possible.
| Pounds lost: 6.4