Q: Are there benefits to leaving some of my flower stems and ornamental grasses standing throughout the winter?
A: Yes there are. Plants that have been affected by disease should be removed, but healthy plants can be left all winter and well into spring. Aside from sparing yourself the last-minute frenzy of cleaning garden beds before the first lasting snowfall, flower stems and grasses provide critical habitat for many beneficial insects, such as butterflies and native bees, that nest in stems or seek protection and shelter under leaves or at the bases of plants.
Monarch butterflies migrate to warmer places for winter, but there are a variety of others that overwinter in Minnesota in chrysalis and even adult phases of their life cycle. They need leaf litter and crevices until the hours of daylight lengthen if they are to survive our long, cold winters. The same is true for lady bugs that will hunker down in groups of just a few to hundreds.
Standing garden beds provide food and cover for birds, as well. They offer a readily available source of protein when it is most critically needed, in the form of insects and their larvae, for chickadees, wrens, and nuthatches that are skilled foragers of the dried upright stems. Juncos and goldfinches will also feast on seeds and berries still clinging to a flower head or vine.
Once spring comes, cleaning up too early can kill the pollinators you’ve been harboring over the winter. Leaf piles may harbor butterflies and other beneficial insects that will not fly until warm nights return. If you’re trying to help some of our native bees that nest in hollow plant stems, experts recommend that you leave dead, broken stems for two whole years so the bees can complete their life cycle. They’ll nest in this year’s stems next summer, and the young bees will emerge the following summer.
If leaving the broken stems seems unsightly in your garden, you can make a pile or bundle of stems and leave them in an inconspicuous place in the yard, preferably a spot with part shade. For cavity-nesting bees, you can even put up a bee house. There’s more information about bee houses — and other information about pollinator-friendly landscapes — here: extension.umn.edu/lawns-and-landscapes/flowers-pollinators.