University of Wisconsin - Extension

Spending a November afternoon on some basic garden clean-up and winter protection chores can increase the chances that your perennials will survive a long, cold Wisconsin winter, according to Dr. Robert Tomesh, a horticulture specialist at University of Wisconsin-Extension.

Perennial gardens have become increasingly popular because they don't require planting every year. But, many perennial plants need a little help getting ready for winter. Horticulture specialists at UW-Extension recommend that you start by selecting winter hardy perennials and planting them in well-drained locations.

In November, when the ground is getting "crunchy" but is not yet frozen, cover perennials with mulch. After leaves and stems have frozen, cut stems back to about six inches. Then place a four- to six-inch layer of loose materials like straw, marsh hay, compost or pine needles over the plants.

This protects the "crowns," or below ground growing points of the plants, and helps keep the soil frozen all winter. Without mulch, the soil may thaw and refreeze during late winter. This alternate thawing and freezing damages many perennials, especially those with shallow buds and roots.

Some more tender perennials, like chrysanthemums, need even more protection. After most of the leaves have turned brown, mound soil about eight inches over the base of the plants. Cut stems back to 10 inches above the soil line. After the soil mound begins to freeze, cover it with four to six inches of straw, marsh hay, compost, pine needles, or evergreen boughs. Do not use whole leaves, especially maple leaves. They tend to mat down and freeze together. This can smother the plant.

For more information about perennial gardens, ask for UW-Extension publication Growing Perennials (E1984) at your county UW-Extension Office. The publication can also be viewed on the Cooperative Extension Web site at http://www1.uwex.edu/ces/pubs/index.cfm.