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Last year was the perfect storm for evergreen trees. Drought-like conditions in the summer and fall shifted into a particularly cold and windy winter, and many arborvitaes, spruce and yews got a stiff beating.
Even Steve Thompson, a veteran arborist for Rainbow Treecare in Minnetonka, had two scorched arborvitaes last winter, although he babies his evergreens with weekly waterings, diligent mulching and delicate pruning. Despite his best efforts, there they were: big patches of rust-brown foliage where he once had lush, green needles.
In the tree care industry this browning, called "winter burn" or "winter scorch," occurs when evergreens start to photosynthesize on warm, sunny days, but then lose too much moisture and dry out.
So this winter, Thompson is going to wrap four of his arborvitaes -- the two that got scorched last year, and another two that are looking puny -- in burlap.
"Burlap, to me, is the last measure of protection," he said. "When all else fails, there's burlap."
The burlap solution seems to be big this season. John Lloyd, science director at Rainbow Treecare in Minnetonka, said the company has gotten a large volume of calls from people inquiring about burlap wrapping services for their trees, perhaps spurred by last year's brutal conditions. "People tend to get motivated when something happens, and last year was a very extreme year," he said.
On warm, sunny days, when light is reflecting off snow and light-colored buildings, a shielding of burlap can keep wimpy evergreens from photosynthesizing, said Jeff Gillman, associate professor of horticulture at the University of Minnesota. "Burlap essentially acts as a sun umbrella, because once your tree heats up, its pores will begin to lose moisture, and then you're on your way to winter scorch."
Obviously, no one likes a tall tent of brown fabric in the yard. "You definitely wouldn't mistake it for a new kind of Christmas decoration," Lloyd said. But under the right circumstances, it's the smart thing to do to keep those boughs green.
Alyssa Ford is a Minneapolis-based freelance writer.
• Your evergreen trees and shrubs appear to be weaker than in past years.
• You have young or recently planted evergreens.
• Your evergreens were pruned hard, especially late in summer or fall.
• You watered inconsistently (or not at all) in the fall.
• Your evergreens are fully exposed to wind from the west.
• Your shrubs are planted so close to the street they could get sloshed with deicing salt.
• Your evergreens are on the south side of a light-colored building, where harsh light can reflect onto them.
• You have delicate varieties, such as hemlock or Northern white cedar.
• Your evergreens are well established and seem to be fine.
• You watered at least once a week during the late summer and fall.
• Your evergreens are fairly well protected from sunlight and wind.
• Your evergreens are planted in good-draining soil with 2 to 4 inches of mulch around the base.