That's a good question! Generally, the seeds in a seed kit will remain viable for two to three years from the date of assembly. As seeds get older, their germination rate falls and the average number of days to germination will rise - so if you have had a seed kit for a couple of years, give it a little more time to germinate.
Critical to seed life is proper storage. Store seed kits where it's cool and dry, for example inside a baggie in the refrigerator, and they will keep longer than at room temperature. Don't store them where its warm and humid; they may want to start germinating inside the seed kit box and then be spent by the time you plant them.
The nutrients have a long shelf life and need no special care. Over time they may crystallize due to evaporation, but that's OK - all of the nutrients still remain inside the packet. After you cut open the packet, add a half teaspoon of water and shake well to return the nutrients to a liquid state. Or just cut the packet open lengthwise and swish it in the AeroGarden water bowl to dissolve out the nutrients.
