Be Kind to Your Evergreens

Filed in Gardening by on March 26, 2014

evergreensI live in Minnesota year round because the winters are so beautiful. I love driving through the countryside after a new-fallen snow or walking through my neighborhood before dogs and cars and plows have gone about their business. I look forward to the time when the hot yellows, reds and oranges of autumn at a last give way to the quiet repose of winter’s white and green; when boughs of spruce, cedar, pine, fir and juniper droop under gentle burdens of white, glistening snow.

But wait… what’s with those evergreen boughs? They’re not all green; some are tan or reddish-brown. What has happened to spoil my perfect winter scene?

When evergreen needles and branches turn brown in late winter and early spring, it’s a sure sign of injury. The winter damage occurs because more moisture is lost through the tree’s needles (transpiration) that is taken up through its roots. The resulting dehydration kills the foliage, which looks as if it has been burned – hence the term “winter burn.”

Several winter conditions can dehydrate evergreens. A warm dry wind during winter months can increase the amount of water lost from leaves and needles. During severely cold weather, the ground may freeze to a depth beyond the extent of the root system, thereby cutting off the supply of water. Temperatures that drop rapidly or oscillate frequently can do even more damage than cold. Above average temperatures may cause damage by breaking the dormancy of plants.

Sounds hopeless, doesn’t it? After all, we can’t control the weather. But there are things we can do to help prevent winter injury to evergreens. For one, we can make good choices when planting. Selecting plants that are in the appropriate hardiness zone is a start. Evergreen species such as black spruce and jack pine are hardier and less vulnerable to winter injury than conifers such as red and white pine and Colorado blue spruce. And we can choose the right planting location. Plants on the south- or west-facing sides of buildings and fences or in exposed areas are more prone to injury.

Even well-chosen and well-placed evergreens, however, benefit from tender loving care in the autumn. Avoid late summer or early fall fertilization while plants are still active, as this stimulates growth which is easily killed by cold. Proper watering is important so roots will have sufficient moisture to offset water loss through transpiration. Reduce the amount of watering in late summer so proper hardening off can occur, and then water when just before freeze-up; evergreens will go into winter better prepared to withstand dehydration.

Mulch plants to increase moisture retention and prevent alternate freezing and thawing of soil In windy locations, put up a physical barrier to break the force of the wind to reduce the risk of dehydration. One can even wrap smaller trees and shrubs in burlap to protect them from winter winds. This practice results in shrubs that look like little brown mummies, but it eliminates winter burn. (Ever notice the wrapped evergreens along the stretch of road that runs along Lake Superior on the north end of Duluth?)

During winter months, cover evergreen or tender shrubs with fresh snow and add more snow whenever shoveling walks. (Do not use hard snow or snow that contains de-icing salt.) Snow provides moisture and acts as insulation to prevent damage caused by freezing and thawing during and after winter warm spells. Heavy snow or ice on  evergreens, however, can result in breakage. So after a wet, heavy snowfall, remove snow from branches that appear to heavy laden.

But spring is coming, you say, and you evergreens didn’t get any preventative maintenance. What now? If you’re lucky, winter conditions didn’t conspire to break evergreen boughs or dehydrate your plants. Even if numerous needles were lost, the buds are usually protected and will emerge in the spring.

And you can take steps to repair damage that has occurred. As soon as the ground thaws, water evergreens well if they are showing signs of winter injury. Injured trees are slow to begin growth, so wait to prune until you’re sure which branches are dead. Once new growth appears, stimulate the plant with a light application of fertilizer. When buds break and you can clearly differentiate damaged from healthy branches, prune out damage portions of the evergreen. Be kind to your evergreens and they will do you proud.

by Reba Gilliand, a Master Gardener in West Otter Tail County.


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