Tuesday’s full moon shines on April Fool’s Day. As the first full moon after the vernal equinox, it determines the moveable holiday of Easter—always the first Sunday after the full moon closest to the spring equinox. This ancient holiday of rebirth, welcoming the new life of flowering plants and baby animals, also mingles with Christian traditions.

As more and more wildflowers brighten the landscape, many trees and shrubs are also in bloom. The dogwood along…