It’s a peculiar rite of modern homeownership: Plant a tulip bulb in autumn, cage or spray it to deter nibblers, admire its fleeting blooms a few months later, let it rot in soil ill-suited to its needs and repeat the whole cycle again the following year.

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

Sitting on her porch in the desert one afternoon while recovering from surgery, Christine Hass closed her eyes. The operation to fix her detached retina had been difficult, and she sought respite from the lingering pain. “Suddenly I could hear all the birds singing. It was March—the migrants were...