They start losing flavor as soon as you grind them. I dry them cut in half and store that way. I grind them as the need arises, you retain much more flavor that way. I do the same with the garlic I dry, I dry them as little chips, store and grind into powder as needed.
I freeze dry my ghosts, jalapeños and habaneros, powder them and store them in vacuum jars. I don't think that they will loose any potency for years!