Wrapping trees for winter protection is not an attempt to keep them ‘warm’ but has the objective to prevent or minimize three sources of winter damage: from desiccating winds, sunscald, and gnawing rodents. Even if the trees in the landscape have survived previous winters unscathed, I would not try to stretch this luck too far. Winters in Minnesota are so unpredictable and variable that even well-established plantings can get hit hard when least expected.
Don’t wrap evergreen trees like a Christmas present with burlap. That has the potential to create more problems than it solves by eliminating too much light and packing the branches too closely together, which often breeds disease problems before the covering gets taken off in the spring. Instead opt for a buffer against the wind and direct sunshine on newly planted or smaller evergreens in the following fashion.
Construct a burlap barrier that is oriented to buffer the winds and direct sunshine from the west or southwest, yet still allow the top to get sufficient sunlight and air. Using anti-desiccants have not proven to be effective in this, in spite of the fact they are still promoted and used by homeowners and professionals alike. The anti-desiccants simply do not have the staying power needed to see them through the long winter months.
Rabbits and voles can cause major damage to trees in the winter. Rabbits can walk across the top of snow cover and nibble branches and girdle the trunk. Voles will work on the trunks of trees under the snow. The tree should be wrapped with commercial tree wrap, plastic tree guards or hardware cloth up to the first branch, and from that point up, the branches sprayed with a repellant like Liquid Fence or Plantskydd. Both will also protect against deer damage in rural areas. Wrapping in this manner will also protect the trees from sunscald.
Sunscald doesn’t actually ‘scald’ the trunk or bark of the tree. Common on newly or recently planted trees, it shows up on the west or southwest side of the thin-barked trees in the spring following the winter months. On cold winter days, the sun can heat up bark to the point where cambial activity is stimulated. When the sun is blocked by a cloud, hill, or building, bark temperature drops rapidly, killing the active tissue and causing a crack in the truck bark.
Newly planted trees should be wrapped for at least two winters and thin-barked species up to five winters or more. Any tree wrapping you’ve applied must be removed in the spring after the last frost. Leaving it on longer creates a moist environment that can attract insects and diseases.
Donna Tatting is a Chisago County Master Gardener