By: Teo Spengler
Are you seeing dead needles appear on the outer edges of your cedars? This could be symptomatic of winter damage to cedars. Winter cold and ice can result in winter damage to trees and shrubs, including Blue Atlas cedar, deodar cedar, and Lebanon cedar. But you may not see the evidence of freeze damage until after temperatures warm and growth starts up again. Read on for information about cedar trees and winter damage.
Cedars are evergreen conifers with needle-like leaves that stay on the tree all winter long. The trees go through “hardening off” in the autumn to prepare them for winter’s worst. The trees close down growth and slow transpiration and consumption of nutrients.
You need to think about cedar trees and winter damage after you experience a few warm days in winter. Winter damage to cedars occurs when cedars are warmed all day by winter sun. Cedar trees damaged in winter are those that receive enough sunshine to make the needle cells thaw.
Winter damage to trees and shrubs happens the same day the foliage thaws. The temperature drops at night and the needle cells freeze again. They burst as they refreeze and, in time, die off.
This results in the winter damage to cedars you see in spring, like dead foliage. Read on for information about the steps you should take to begin repairing winter damage on cedar.
You won’t be able to tell right away if the weather has caused winter damage to trees and shrubs, since all cedars lose some needles in fall. Don’t take any action to start repairing winter damage on cedar trees until you can inspect the new spring growth.
Instead of pruning in spring, fertilize the trees with landscape tree food, then apply liquid feeder to the foliage daily during April and May. At some point in June, evaluate any winter damage that may be present.
You can do this by scratching the stems of the cedars to see if the tissue beneath is green. Prune back any branches where the tissue is brown. Cut back each branch to healthy stems with green tissue.
Once you have removed winter damage in trees and shrubs, prune the cedars to shape them. Cedars usually grow in an uneven pyramid shape and, as you cut, you should follow that shape. Leave the low branches long, then shorten the branch length as you move toward the top of the tree.
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Many plants can use some protection from the winter elements to come back healthy and strong in the spring. Winter winds can be especially damaging to plants. They can snap stems and branches, as well as target the plants with frigid cold air and be extremely drying. But there are several methods available for winter plant protection—including shelters, wraps, and mulch—that you can implement as you go about your fall garden care.
The ravages of a Maine winter play havoc with the garden’s trees and shrubs. Winter sun, wind and cold can bleach and desiccate evergreen foliage, damage bark and injure or kill branches, flower buds and roots. Hungry mice burrow beneath the snow to feed on bark and twigs while deer and rabbits nosh on flower buds and foliage.
What can the gardener do to mitigate this damage?
On cold, sunny days, the bark exposed to direct sunlight (usually the south and southwestern sides of the tree) heats up to the point where living cells beneath the bark become active. These cells, called cambial cells, are responsible for producing new water and food conduction tissues within the trunk. When the sun becomes blocked by a cloud or building, the bark temperature drops precipitously, killing the cambial cells. The resulting damage is called sunscald.
Sunscald is characterized by sunken, dried or cracked areas of dead bark. Young trees and newly planted trees are highly susceptible, as are thin-barked trees such as cherries, crab apples, maples, birches and mountain ash. Also, pruning evergreen trees or shrubs in late summer or fall to remove lower branches may expose previously shaded trunk tissue to direct winter sun, resulting in potential sunscald injury.
Protect sensitive trees by wrapping the trunk with light-colored material that will reflect sunlight, keeping the bark temperature more constant. Commercial tree wrap, a polyurethane spiral wrap that expands as the tree grows, or any light-colored material will work. Wrap the tree in early November and remove the wrap in April.
Newly planted trees should be wrapped each winter for at least the first two years, thin-barked species for five years or more.
There is no remedy for sunscald after it has occurred, other than to carefully cut away the damaged bark with a sharp pruning knife and hope for the tree’s natural wound-healing capacity to work. Do make damaged trees a priority for wrapping in subsequent winters.
Whenever the winter sun warms conifer needles, transpiration occurs. Water is lost from the needles while the roots are frozen, and this results in desiccation of the needles and destruction of chlorophyll, followed by needle browning or bleaching. Browning or bleaching of broad-leaved evergreens, such as rhododendrons, occurs in the same manner.
Among the conifers, the most susceptible types are yews, arborvitae (Mainers call it “cedar”) and hemlock. All conifers, however, can be affected.
Solutions to this problem begin with proper placement of conifers and broad-leaved evergreens in the landscape. They are best planted on the east side of buildings, certainly not on the south or southwest sides or in windy, sunny sites.
To protect low-growing conifers from winter wind and sun, prop pine boughs against or over the plants once the ground has frozen. The boughs will act as a windbreak and catch insulating snow.
For larger conifers and sensitive rhododendrons, burlap wind barriers can be constructed on the south, southwest and windward sides of plantings. These barriers, if tall enough, also may protect against salt-spray damage to plants near driveways and roads.
Stakes for the barriers should be installed in early November, before the ground freezes. Later in the month, attach the burlap sheets to the stakes with staples or sturdy twine. Make the enclosure as tall as feasible to block wind from hitting the uppermost branches. Leave the top of the enclosure open.
Water-stressed trees and shrubs are ill-prepared for winter winds and cold. Throughout the growing season, your trees should receive an inch of water a week from rain or irrigation. Beginning in late autumn until freeze-up, they should receive an inch of water per month by rain or irrigation. Waiting until October to begin watering as needed will not maximize stress resistance.
Some gardeners spray evergreens with anti-desiccants or anti-transpirants to reduce winter damage. Save your money. Most studies show these materials to be ineffective.
Most of our garden mice spend the winter in the woodpile below the porch sunflower feeders. In a really hard winter, however, we have experienced mice damage on the lower trunks of newly planted shrubs and trees, enough to start placing cylinders of quarter-inch hardware cloth around the bases of sensitive plants. To be effective, these wire cylinders must extend two to three inches below ground.
Cylinders made of the same wire will deter the garden’s rabbits from feeding on specific shrubs or trees, but they should extend at least 18-24 inches above the ground to deter nibbling of tender lower branches. In all cases, these wire barricades may be left in place all year, but be sure to enlarge them as the trunks grows larger.
As for the noshing deer, we built a fence to keep them away from the blueberries and raspberries. Beyond that solution, you’re on your own. In my mind, deer at the edges of the winter garden are part of the joy of gardening in Maine.
Broadleaf evergreens can dry out in winter
The main cause of winter damage to trees and shrubs is through dessication, or drying out. When the ground freezes, plant roots are unable to take up water from the soil, so they quickly begin to use up all the water stored in their leaves and stems. This is very damaging, particularly to evergreen trees and shrubs that don’t protect themselves by dropping their leaves in winter.
Anti-desiccants are products that can be applied to evergreen trees and shrubs to help hold in moisture through the winter. If you have problems with cold damage in your garden, you may want to give them a try.
Apply on a relatively warm day
Anti-desiccants, also called anti-transpirants, are sprays that provide a protective coating to evergreen foliage that reduces the amount of water that escapes. Anti-desiccants such as Moisturin are made of chemical polymers, and products such as Wilt Pruf are made from pine oil.
Anti-desiccants are gradually washed and worn away over several months, so by springtime they’re gone. While all anti-desiccants are marketed as biodegradable, the ones with the most natural ingredients will be safest for you and your plants.
In areas with harsh winters, anti-desiccants are applied twice, in November/December and again in February. In areas with more moderate winters, one application in December or January should see you through the coldest months.
Anti-dessicants are most often used on:
Caution: Don’t spray waxy-blue conifers such as blue spruce – they already have a natural coating that you don’t want to damage.
Follow all package instructions with your anti-desiccant, and also keep in mind these tips:
If you have spray left over, hang on to it. Anti-desiccants can also be used for:
Causes of cold damage on plants include:
Keep your hands off the pruners until you see green buds on your evergreen tree or shrub. Just because they aren't deciduous, doesn't mean that evergreens don't lose their leaves or needles. In cases where the foliage has browned but the branches didn't die off, new growth will cover or dislodge old, brown needles. Once buds break, branch tips -- or even whole branches -- that remain brown can be cut back to an outward facing bud or side branch below the dead material with pruning tools sterilized with household antiseptic cleaner.