When to apply crabgrass killer. How often do trees need to be watered? When plants are okay to be left uncovered. Will tulips grow back after animal damage? When will hummingbirds arrive? Protecting pollinators during spring yard cleanup. When grass seed can be planted after applying crabgrass killer. How to best prune peonies. Repotting a Christmas Cactus. Signs of Emerald Ash Borer damage. Learn more from horticulturalist Mary Meyer at extension.umn.edu.