Trouble With The Spreader

I will place this experience into the "live and learn" category.  In early summer I placed fertilizer on my yard and I somehow had a lot leftover in my spreader when I was finished.  I didn't think much of it and left it sitting in my spreader all summer.  Thursday I tried to clean it out in order to use the spreader for fall fertilizing and weed killer.  To my surprise, the fertilizer from the summer was rock solid, jamming up my spreader.  This is odd to me because I have the exact same fertilizer sitting in my garage in a non-sealed bag and it didn't get hard at all.  I tried to get it out with a mini-shovel and when that didn't work I decided to spray it with water to soften it up.  This worked, except that it made the fertilizer quite sticky, jamming up the spreader again.  I didn't realize this until I had already poured the fall fertilizer into the bin.  So I had to remove it and place it in a trash bag so that I could manually move the fertilizer from the spreader that was getting stuck.  I finally got the fall fertilizer on the yard.  It just took me about 30 minutes longer than expected.