NPK fertilizer=No Plants Killed— When you stroll the shelves of your local garden center, your 5th-grade science class might come back to haunt you. You might be left standing at the fertilizer aisle wishing you had paid more attention to Charlie Brown’s teacher when she was rattling off those elements and their letter symbols. Now for the life of you, you can’t remember what they all mean. All you want is a ‘green thumb’ to prove to the guy next door that you’re a ‘real gardener.’ So what’s with all the mumbo…