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Perennials: When to Cut Back for the Winter

Eli Sagor
Flickr - Creative Commons

Most perennials can be cut back in the fall, but some are better left uncut, depending on how active they are during the winter months.

Ornamental grasses, cone flower, Black-Eyed-Susan, and Black-berry Lilies have seed heads that provide bird food during the winter, so they are better left uncut until late winter or spring.

The snows this fall smashed some ornamental grasses, which can be cut back now. A power hedge trimmer cuts through most ornamental grasses. Cut the grass clump about four to six inches above the soil. Grasses that were not damaged by the snow, like Blue Oat Grass, can be left and cut back next spring.

Now that Hostas are frozen, they can be cut to the ground before the next wind blows away their freeze-dried leaves. Trim the ugly leaves off of other foliage plants like brunnera or bergenia. The remaining leaves can be left until spring. 

Trim other perennials back to their basal leaves. Because Asters had a lot of powdery mildew this fall they can be cut to the ground.    

Cut flowering shrubs back after they’ve bloomed. Autumn is a good time to prune the flowers off of blue mist spirea, Russian sage and summer blooming spirea. In the spring trim out any winter die back, but don’t prune spring blooming spirea or lilacs. 

Old pine and spruce need extra water going into our driest season, winter. Soak the entire root zone. The roots on a forty foot tall spruce grow more than forty feet in diameter around the tree. Be sure to water as much of the root zone as possible.

Take the tree leaves off of lawn areas. Over winter the molding leaves will leave dead spots in the grass; but leaves in perennial and shrub beds can be left as they are to provide mulch insulation unless the trees had leaf diseases during the summer. By next spring the leaves will need to be taken out of the landscape beds and composted. 

Tom has been offering garden advice on KUNC for almost two decades. During that time he has been the wholesale sales manager at Ft. Collins Nursery, Inc. Since January of 2005 he has been the owner and operator of Throgmorton Plant Management, LLC., a landscape installation and maintenance company as well as a horticultural consulting firm. He lives in northern Ft. Collins with his wife and two kids.
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