They were like moths to a flame or, more accurately, butterflies to a native plant. No sooner had I unloaded two joe-pye weed perennials from my car last August than three tiger swallowtails dive-bombed the pots, as if to validate my purchase. If only my fellow shoppers knew what they were missing...

Of all the surprising twists and turns my venture into the world of wildlife gardening has taken, the one that stands out most is the day I learned about the dark side of my favorite symbol of hope and summer: the sunflower. It was in the early 2000s and the fledgling gardens at my new home were...