A humane backyard is a safe haven for wildlife—a space where animals can thrive free from pesticides, trapping and other threats.

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...