Dr. Grow: Remember evergreens when readying garden for winter

We have been blessed with some absolutely beautiful days this fall. The temperatures have been above normal and the sky has been mostly sunny. This weather lures every gardener out of the house into the yard ready to garden and landscape for winter.

There are a lot of things to do right now, such as winterizing the lawn and raking leaves. Then there are things to do later, like planting fall bulbs, cutting back roses, and mulching the landscape.

Unfortunately in the fall we often overlook the needs of some of the most common foundation plants in our landscape -- broadleaf evergreens. Included in this group of plants are boxwood, azalea, rhododendron, holly, and southern magnolias.

Because these plants are not deciduous (they don't lose their leaves in the winter), they have unique physiological characteristics that require knowledge and care on the part of the gardener in order for broadleaf evergreens to continually survive in the region.

Since broadleaf evergreens do not drop their leaves, they will continue to photosynthesize all winter long. The rate of photosynthesis depends upon daytime temperatures and light conditions. If temperatures reach into the 40s and 50s on sunny days during some mid-winter warming trends, then photosynthesis will occur.

In addition, broadleaf evergreens will transpire on sunny days. Leaves have small pores on their surface called stomata. These pores open and close depending upon sunlight and to some extent upon temperature. On sunny days, stomata tend to open and remain open.

The stomata are the openings through which oxygen, produced by the plant during photosynthesis, exits the plant. They are also the pores by which carbon dioxide enters the plant. Carbon dioxide is used by the plant during photosynthesis to produce sugars. Finally the stomata are also the openings through which water is lost, a process called transpiration.

The water lost through plant stomata is in the form of water vapor. This lost water vapor is replaced by water moving from the soil through plant roots into the plant stem and finally into the plant leaf. During most of the year, except during droughts, there is enough moisture in the soil to act as a reservoir and supply moisture to the transpiring leaves.

During a drought, water continues to be lost through the stomata. If there is no water in the soil reservoir to replenish the lost moisture, the dessication that results causes leaf burn.

An artificial drought can occur in broadleaf evergreens during a severe winter in Southeast Missouri. During cold, sunny days, the stomata in the leaves of broadleaf evergreens will open and some transpiration will occur. If the soils are frozen, water can not move from the soil into the plant and replenish the moisture lost in the leaf. Dessication will occur and leaves will burn. If the dessication is severe enough, the plant will die.

So, how do you protect your broadleaf evergreens during the winter? If the fall is dry, water your evergreen plants before temperatures really drop. If the winter remains dry, water your evergreen plants occasionally throughout the winter during warm spells.

Secondly, spray your evergreen shrubs one time in the late fall with an antitranspirant. The antitranspirant clogs the stomata and reduces the amount of moisture lost through transpiration. This reduces the possibility of winter burn. There are several antitranspirants on the market. Ask the clerk at your local garden center about the one that they carry. Be sure to follow label directions.

Be sure to spray the antitranspirant late in the fall after the temperatures have really gotten colder. I usually wait until late November or early December to make the application. Just a few minutes of effort in the late fall can help the broadleaf evergreens in your landscape make it through the winter.

Paul Schnare of Cape Girardeau has been in the lawn and garden business for more than 20 years. He's an adjunct professor in horticulture at Southeast Missouri State University.