I always leave some of my perennials standing through the winter for several reasons. Various stems of taller plants poking up through the snow provide great winter interest along with other ornamental trees and shrubs. More importantly, leaving plants up provides a number of benefits to birds during our long and chilly Minnesota winters. Seed heads can make a great food source for birds and stems can providing additional hiding places out of the wind or away from predators.
Grasses are great for providing both food and winter coverage with their long sturdy stems and flower heads. Many other perennials such as coneflowers, liatris, and black-eyed Susan also produce seeds for the birds to enjoy. Cosmos, zinnias and coreopsis are also some annual favorites of the birds in winter. So go ahead and put your garden to bed for the winter, but leave a few treats for our feathered friends.