(Credit: University of New Hampshire)

Many of our perennial garden flowers and ornamental plants have been selected for flower color, size, form, and other attributes rather than for their ability to endure severe winter conditions. While nature is concerned with the survival of the fittest, we are not pleased when we find that nature has not chosen our favorite plants for survival. Therefore, winter protection of some sort becomes important to ensure that certain plants will survive our midwestern winters.

Since many of our ornamental plants can suffer winter damage at our latitude, protection of some type is advisable. (credit: University of New Hampshire)

Plants that have been located in sites not well adapted to their needs also are more susceptible to winter damage. Too much shade for some, too little shade for others, poor soil drainage, or other environmental problems can lead to winter damage.

If these plants were growing in the wild without any human intervention, many would disappear. In other cases, nature would cover them with a layer of leaves or other plants would be growing close to them that might provide winter protection. In our gardens and landscapes, a cleaner look is desired so fallen leaves normally are removed since they often will not say where we want them and will scatter throughout the yard. Additionally, some plants cannot endure the competition of other plants near them, so we keep them more isolated.

Mulches provide the best winter protection for many species of perennial plants. As soon as growth has ceased and temperatures are cold enough for slight soil freezing, mulches should be applied. However, not all plants need to be covered. Durable, hardy perennials such as peonies, iris, and daylilies will survive without it. Nevertheless, covers are still beneficial for moisture retention and weed control.

The main purpose of a winter covering on sensitive perennial flowers or marginal woody plants is not to conserve warmth. Rather, covers prevent abrupt wild temperature fluctuations at the base of the plant and in the upper root zone. For smaller plants that may not yet be well established, an important function of covers comes in late winter and early spring. During those times, unprotected soil alternately freezes and thaws, often in rapid succession. As soil freezes it expands and, conversely, as it thaws it contracts. This results in the possibility of the roots of small plants being "heaved" up, exposed to the environment, and drying out. This is very common on shallow rooted plant such as chrysanthemum, Shasta daisy, or small bulbs such as crocus. This problem is most common in heavy clay soils which have not been improved via the addition of organic matter. It generally is not a problem in light, sandy soils.

In many cases, the objective of winter protection is not to keep plants warm, but to prevent alternate freezing and thawing. (Caption: Pixabay)

Pine needles, wood chips, straw, and compost are all useful materials for mulching. Most of these items are too dense to put directly over the crowns of herbaceous perennials that maintain green growth during the winter such as chrysanthemum, oriental poppy or tritoma. Straw or evergreen branches placed directly over the plants provide some protection yet allow light and air to penetrate. Other materials might be placed on the soil around plants. Stiff oak leaves make a useful mulch, but often need some means for holding them in place or they may blow away and expose plants during cold, windy weather. Soft leaves, such as maple or ash, become too soft and soggy during the winter and can suffocate small plants or tender shoots.

Pine needles (sold as pine straw) make a very useful mulch for winter plant protection. (Caption: Free Pik)

Coverings of loose materials for winter protection should be at least two inches in depth. Check both the mulch and the condition of the plants below on mild winter days. Even after the holidays, it is not too late to add additional covering of leftover holiday greenery, should your plants need them.

Coverings of loose materials such as straw should be about two inches in depth for optimal winter protection. (Caption: Pixabay)