Shelf life of fertilizer
Can anyone tell me how long fertilizer should last once the bag has been opened?
Welcome, Molly! I'm glad you found us! 
I think the answer to your question will vary tremendously, depending on the type of fertilizer and perhaps the form it's in, as well as the conditions under which it has been stored.
I think the answer to your question will vary tremendously, depending on the type of fertilizer and perhaps the form it's in, as well as the conditions under which it has been stored.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams