When you plant perennial flowers, you want them to grow and bloom year after year. The first step toward achieving this goal is to choose perennials that are rated winter hardy for the area where you live. The southern one-third of Minnesota is located in USDA Winter Hardiness Zone 4, while the northern two-thirds are located in Zone 3. Avoiding poorly drained sites, where water collects and stands after a rain, is also critical to winter survival for most perennials.

If you have chosen plants hardy for your region and planted them in well-drained soil, the best strategy to promote winter survival is the use of mulch. Apply a winter mulch in late fall, after there is some frost in the ground. Suitable mulch materials include four to six inches of straw, marsh hay, pine needles, compost or shredded leaves, or two to four inches of wood chips. Use only shredded leaves, as unshredded leaves tend to mat down over time, providing little insulation.

Mulch is important not only to protect perennials from cold, but also from warmer fluctuating temperatures. In years of little or no snow cover, bare soil may thaw during warm winter weather. This can lead to premature growth of some plants, or when the soil refreezes, cause heaving, which damages plants. Mulch protects the "crowns" or growing points of the plants and keeps the soil frozen all winter, even without adequate snow cover.

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