Q: How long can fertilizer be stored before it loses its effectiveness?
A: One of my jobs as a child was to put chunks of old fertilizer on a sheet of roofing tin so my father could run over it with his truck. He knew that if it is kept dry, fertilizer remains effective for years, maybe decades. The problem with aged fertilizer is when it gets lumpy or slimy from high humidity. You can beat it to pieces with a hammer in a bucket and use it as you normally would. Slimy fertilizer can be thrown lightly under shrubs and trees this spring. They will be delighted by the unexpected treat.