In general, what is the shelf life of seeds? I know it differs by seed and under what conditions they are kept, but will most still be good in a year or two if they're kept cool and dry?

Typically, most seeds kept cool and dry will remain viable for 2 years- after that you'll see about a 50% decrease in viability each year- in other words, if you have seeds that are 3 years old, probably only 10 out of 20 will sprout, at 4 years, about 5 will grow- but some seeds will remain quite viable for as long as ten years- I had excellent sprouting rates with some herb and flower seeds my mother had packed away nearly ten years earlier- my off the cuff observation has been that the smaller the seed, the longer its shelf life.

Archaeologists found viable wheat seeds in the pyramids, thousands of years old. They think it was the combination of very dry, very dark, and not much oxygen. I've kept seeds in the back of the refrigerator and four years later when I got around to planting them, had about 30% germination.

Thank you both!!