Getting trees ready for the rigors of cold weather is a multifaceted undertaking, depending on factors such as the species, health and location of the tree, as well as the local climate. There are some general winterization tasks that tree care pros should keep in mind as they survey clients’ trees during the fall months.
“The two most important things to do, really, are winter watering and protecting against sunscald,” says Matthew Johnson with ArborScape, Inc., Morrison, Colo. “Winter watering is crucial to give trees a head start on the next growing season, and it’s also the thing that people least think about doing,” he explains. “People just don’t think about their trees in January, especially here in Colorado.”
January and September are historically the two driest months in the area and the arid climate can stress trees. “It may be different in other cold states, like Ohio or Massachusetts, but it’s so dry here in the winter that trees can get stressed. By the time people start thinking about their trees in April or May, they’re already behind the eight ball,” says Johnson. ArborScape suggests a winter watering schedule to its customers, typically once per month, or will provide the service. “The service is good because it takes away the ‘I’ll do it tomorrow’ factor. Plus, we have the right equipment to make it easy,” he says. “We just drive the truck up and typically inject about 30 gallons into the rootzone.”
Sun scald is another concern. “We can have days where it’s 5 degrees in the morning and gets up to 50 degrees. When the temperature drops again, it can create splits in the bark,” says Johnson. To stabilize bark temperatures, ArborScape recommends using a light-colored tape to protect young trees. The tape is wrapped around the tree as high as the first branch. “It’s crucial to take that tape off after winter. We advise doing it before Easter because it can also attract pests and create other problems,” he adds.
For trees, especially evergreens, near streets where magnesium chloride might be used as a road deicer, precautions should be taken to block road splash from coming near the tree. “It hurts the foliage, as well as getting into the rootzone, where it is taken up by the tree. It causes a distinct defoliation, and over time will damage a tree,” says Johnson.
Finally, says Johnson, now is the time to act to prevent damage from heavy snow loads on trees. “Keeping a tree trimmed is the best way to prevent snow damage, it keeps the snow from building up,” he explains. ArborScape Services advises that fall is a good time to deadwood and thin trees, in part because the structure of the tree is easily visible with the foliage gone. Getting rid of dead branches and taking weight off live branches can help the tree come through heavy winter snow and windstorms with fewer problems.
Olivia Lenahan, horticulturist with Iowa State University Extension, says that fall is also a time to consider the fertility needs of trees. “Most established trees don’t really need fertilization, they should be able to get what they need from the soil, but for newly planted trees and trees that are more susceptible, it may help to put down some balanced fertilizer,” she explains.
She cautions that this should only be done for trees that displayed signs of yellowing or limited growth during the growing season. “Early fall is an OK time to put the fertilizer down, but you have to be careful with fertilizing right before winter, because you don’t want the tree to be putting on new tender growth right before winter,” Lenahan adds.
In states like Iowa, she says, strong winter winds can lead to desiccation injuries. One way to offer protection is to put up barriers in the fall to protect susceptible species. “Broad-leafed evergreen species will continue to transpire during the winter, and if the ground is frozen, the roots aren’t replenishing that loss,” she explains. “It’s often overlooked, but watering is important. Even if it’s not a broad-leafed species, any tree that’s newly planted is stressed, and I think people underestimate how much those types of trees need water.” She recommends watering before the ground freezes, and not to apply too much water, which could lead to root rot and other problems.
Young trees are also particularly vulnerable to four-legged creatures eager for a meal. While there are a number of repellent sprays on the market, Lenahan says that good, old-fashioned chicken wire, or a similar product, can offer more reliable protection against rabbits and deer in the winter. “I’ve tried using the sprays, and they are effective if you’re consistent, but you need to keep spraying, and they’re not as effective in the cold, or if it rains or snows,” she says. “If you put a chicken wire fence up in the fall, then the only thing you have to watch out for is if the snow line gets too high and they can hop over or climb under it.”
Likewise, Pat Williams, a horticulturist with Johnson’s Nursery in Menomonee Falls, Wis., says that protecting trees against damage from animals is an important part of late-season tree prep. “For example, in the fall, deer can rub up against any young tree with smooth bark and rip the bark right off the tree,” she explains. “If the bark gets rubbed off all the way around the tree, it will die.” She adds that rabbits and voles can also damage trees by eating the bark. “They tend to prefer the bark of fruit trees, which would include all flowering crabapples,” she explains.
To help prevent this type of damage, Williams recommends all young trees be protected with a tree guard. “Those plastic spiral guards are so cheap and so easy to use that they just make sense,” she says. “You just wrap them on in the fall and then unwrap them in the spring.” She cautions against leaving the guards on year-round, because mold and fungus can grow beneath them during the summer. Two guards may be required to cover the tree high enough to prevent buck-rub damage.
Checking and topping off mulch in the fall can also prevent winter damage. “A 3 to 4-inch layer of mulch is good for trees year-round. In the summer months, it helps preserve soil moisture; in the winter, it helps to insulate against the freezing and thawing that happens in the top few inches of soil all winter long,” says Williams. Mulch helps keep soil temperature more constant once the ground freezes. She advises against piling mulch directly against the trunk of the tree, which in the winter allows rodents easy burrowing access to the bark. Rather, she says, place mulch around the tree and install a plastic tree guard to protect the bark.
Williams says that winter prep sometimes needs to start in the spring, during planting season. “Snow load is one factor to consider before planting. Arborvitae, for example, do not sustain snow load very well. Their branches are a little finer and break a little easier than, say, a yew or boxwood, when planted along a foundation where snow will fall off the roof,” she explains. The same caution goes for planting fragile species in areas where snow will be plowed or blown. Planning ahead for winter weather can give trees the best chance to survive the cold and thrive when spring finally comes.