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What is the crazy weather doing to perennials?

Welcome to the rollercoaster of our Minnesota winter!

This year we have had temperature extremes that can vary 50 degrees in 24 hours. Add to this the slim to none snow cover and we are looking at a long winter that may severely impact some of our most hardy herbaceous perennials, trees and shrubs.

Winter injury may be caused by a complex combination of circumstances rather than a single factor, and the extent of injury will also vary. These elements include deviation from normal minimum winter temperatures, dramatic fluctuations in winter temperatures, length of a severely cold period, time of year that the severe cold period occurs, bright sunny days with frozen soil, depth to which soil freezes, drying winds, low humidity, snow cover, plant hardiness and plant location.

The various symptoms you might see include:

• Bud and stem damage can occur when temperatures dip below their hardiness. Some floret buds or tips can be partially or completely killed. If this happens, there may not be a full complement of flowers on the plants.

• Wind and sun scald, occurs in periods of severe cold or extended cold weather combined with bright sunshine. Alone or in combination, can damage evergreens because they cause the plants to transpire or lose water through their leaves. The water is not replaced because the roots cannot pick up water in cold or frozen soil. Leaves turn brown, starting with brown edges or needle tips and progressing between the veins or down the needles. These maladies may be prevented by protecting the plant from the wind or shading the plant.

· Sun and wind scald of bark (maples are particularly susceptible) occurs on sunny days in winter when the bark of a tree is warmed by the sun, especially on the southwest side of the trunk. The bark often cracks open, or it may separate from the tree without splitting. Sunscald is more prevalent on stressed, recently transplanted, smooth- or thin-barked trees.

• Freeze-thaw cycles without adequate snow cover can damage the roots of even hardy herbaceous perennials.

The result of winter injury sometimes takes months or years to appear. Sometimes the leaves live on until their reserves are depleted. This can occur slowly in cool weather or rapidly when the weather suddenly becomes hot. Winter-damaged tissue may allow disease organisms and insects to enter. Root systems, especially shallow ones, may be injured by cold. The damaged root systems fail, and the top of the plant may thin and start to die.

Think ahead to alleviate the effects of brutal winters such as this.

Keep plants healthy by proper maintenance. Timely pruning, fertilizing, and watering will help your plants make it through the winters. Applying a heavy layer of mulch once the ground freezes, wrapping young trunks exposed to wind and sun, or providing shade or windbreaks to exposed plants, will go a long way to protecting your ornamentals from harsh winters.

Hang on tight; the rollercoaster ride isn't over yet. Looking on the bright side, our days are lengthening, and January seems to be racing by!

Until next time, happy gardening!

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