Hi Michele –
How long seeds last will totally depend on the type of seed and how it is stored. Seeds must be stored completely dry, or you risk moldy seeds. Constant temperatures are best for seed storage, big fluctuations in temperature can stress seeds and cause them to not germinate.
Some seeds are viable longer than other, naturally. Some plants (often classified as noxious weeds) produce a seed that stays viable for 40+ years! Vegetables such as beets, broccoli, cucumbers have a shelf life of 3+ years if stored properly. Tomato seeds can be viable for 5 or more if stored properly. Other vegetables such as peas, celery, and corn are known to have short shelf lives, usually two years or less.
Check out our page on seed viability, the linked chart might give you an idea of how long your seed may be good for. You can see it here:
Hope this helps!
Garden seeds can last anywhere from one to five years on average (and sometimes even longer) depending on the type and variety. However, storing seeds in a cool, dark place with low humidity will further prolong their lives. As seeds begin to expire, their rate of germination decreases, so even if they are old, some seeds may still be viable. If seeds are stored properly, I think it’s safe to say that you can still expect to see them germinate on average, after up to three years.