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Like preparing our homes and automobiles, so should we ready our outdoor plants to withstand the winter months. Applying certain principles and practices beginning in the fall can help reduce the damages of cold, brutal days.
Winter damage to plants can basically be divided into three categories: desiccation, freezing, and breakage. Becoming familiar with these ways will greatly increase the chance that the home gardener will be successful.
Desiccation is a common cause of winter damage
Desiccation simply means drying out, and is a common cause of winter damage, especially for evergreens. This drying out happens when the water leaves plants at a greater rate than that of water being taken in by the roots.
The leaves or needles of evergreens transpire a little moisture even during the winter. On severely cold days the ground may freeze so deep down that the roots cannot take in a supply of water. Factor in a dry fall followed by sunny, windy winter days, and the problem is exacerbated. The warmth of the sun may cause stomates on lower leaves to open which will increase transpiration.
Frost heaving is a phenomenon that occurs when the alternating thawing and freezing of soil pushes shallow-rooted plants out of the ground where the roots can’t get enough water to prevent desiccation.
Freeze can badly damage many plants
There are several ways freezing can damage plants. First, new growth from early fall or late summer pruning or fertilizing may not have time to develop and harden enough to survive sudden drops in temperatures of freezing or below. Ice crystals can form that will rupture cells walls, showing up as dead tips and branches.
Trees can be damaged when a significant temperature change between day and night causes the water within the trunk to freeze. Called frost cracking, the trunk explodes or splits open. Unless severe, the cracks appear to close when warm weather arrives, but the wood fiber inside may not grow back together. This type of injury is common on the southwest side of shade trees as the afternoon creates, even more, extremes between day and night temperatures.
A late freeze in the early spring can badly damage many plants. The flowers or leaf buds are stimulated by the sun and maybe killed by freezing night temperatures. Injury from cold temperatures also occurs on tender trees and shrubs during their dormant period. Flowering shrubs leaves will likely survive but they will probably lose their flower buds.
Plants left outdoors in containers can suffer root injury from cold temperatures. Generally, 28 degrees Fahrenheit is the lethal temperature.
Breakage, the third cause of winter damage in plants usually occurs because of the weight of snow and ice or by careless snow removal. High winds can exacerbate the problem. Damage takes place in the way of miss-shapen plants, split tree trunks, and broken branches.
Preventing Winter Damage in Plants
Planning ahead can help prevent much of the damage caused by winter weather. Begin by selecting plants that are winter hardy in your area. Buying plants from local nurseries is the easiest way to ensure this. Choose an appropriate site for planting. The plant easily injured broadleaf evergreens such as rhododendron, azaleas, and holly on the north or eastern side of a building or barrier so that they have some shelter from winds and winter sun.
Avoid roof overhangs and low spots that can create frost pockets. Place plants away from eaves and areas where snow or ice is likely to accumulate and fall on the plants.
If the fall weather has been dry, give plants a good, deep soaking before the ground freezes. This will help ensure water supply to the root system. Additionally, water on any unseasonably warm days during January, February, and March.
Mulching is a good way to avoid erosion. Apply a 2-inch layer of good mulch to help reduce water loss and increase soil moisture around the roots. To prevent frost heaving, use mulch as a buffer.
Small trees and shrubs can be protected by windbreaks made from burlap or canvas attached to a frame around the plant. Sometimes they may be wrapped in burlap or straw, but avoid using black plastic for wrappings or windbreaks. During the day, heat can build up inside the black plastic causing extreme fluctuations in day and night temperatures. This can speed up the growth of buds that will be susceptible to a late frost.
Put container plants in a protected area or sink them into the ground. They can also be grouped together, or heavily mulched to avoid injury to the roots.
Remove snow collected on shrubs with a broom, sweeping upward. Avoid disturbing frozen brittle branches and wait until a warmer day after some of the ice has melted.
Remove snow to decrease the weight of snow to plants
Repairing Winter Plant Damage
Take care not to confuse a plant’s protective mechanisms with winter damage. Some plants naturally shed or reposition leaves during the cold weather. Others will have wilted-looking leaves all winter. Some evergreens may take on a red, purple, brown or bronze winter color. Look instead for dead branches and tips, broken branches heaved root systems, or discolored evergreen needles.
After new spring growth is the best time to assess winter damage. Scrape branches and look for a green layer underneath. Only remove branches that are obviously dead. Prune dead branches or twigs to one-quarter of an inch above a live bud or to the nearest live branch.
Remember that proper pruning at the appropriate time throughout the year is the best way to prevent winter damage. Consult growing guides to determine these times. Always avoid late summer pruning because doing so will stimulate tender new growth and reduce the plant’s winter nutrient supply.
Discolored narrow-leafed evergreens needles may regain their green color or produce new foliage if not too severely damaged. Broad-leafed evergreens can often produce new leaves. Remove damaged leaves that do not drop. Prune away badly damaged or broken branches. This will reshape the plant and stimulate new growth. To compensate for winter injuries and stimulate new growth, apply a high-quality fertilizer to the soil around the plant.
These measures, along with adequate watering, will usually result in new growth to compensate for winter injuries. Continue giving special care to these plants during the growing season, and remember that just as healthy homes and people best survive the winter weather, so do healthy plants.