I've never been able to keep from shooting it up, so I have no idea
I would guess that as long as its sealed its probably good for many years.
Posted: 9/16/2010 9:03:01 AM EDT
[#3]
Un-mixed, in climate controlled environment: indefinately
If you store the fertilizer in a garage or high humidity environment, it will draw water from the air, expand, and harden into a single clump. Ask me how I know.