Dramatic temperature changes last autumn likely are to blame for the winter injuries, said Del Barton, parks superintendent and arborist for the city of Powell.
“We had some really warm days, so a lot of the trees and shrubs were coming out of dormancy, and then we had an extreme drop in temperatures, well below freezing,” Barton said.
In Powell, the high temperature reached 57 degrees on Nov. 19. Just two days later, the overnight low plunged to 7 degrees below zero.
When the weather is warm, trees try to begin the photosynthesis process, which includes drawing nutrients and water from the ground, Barton said.
“But if the ground is frozen, because of the cold temperatures in winter, the water is not available,” he said. “So what begins to happen is the trees and shrubs start to die because they can’t get the nutrients and water that they need to survive.”
Winter winds didn’t help.
“When you get these cold, dry winds, they actually increase the dryness, and the needles tend to dry out quicker and turn brown,” Barton said. “When you get that combination effect of the dry winds, lack of moisture and nutrients, that tends to create an additional hardship on the plants.”
The winter damage to evergreens is widespread throughout the region.
“A lot of the arborvitae shrubs and Ponderosa pines and Austrian pines seemed to suffer the brunt of it,” Barton said. “I’ve seen a lot of homeowners where their arborvitae shrubs are just totally brown.”
It’s important to resist the urge to prune and remove the rust-colored areas right now.
“First of all, put away the pruners!” wrote Suzanne Larsen, a master gardener in Cody, in a recent gardening article. “All of the information I have been able to find on this subject says we have to wait and see how these plants recover from last fall’s drastic weather change and temperature drop.”
With spring’s arrival, folks are anxious to start yard work and gardening, Barton said.
“Sometimes these plants that have gone through the winter injuries take longer to recover, so rather than to rush out and cut everything down, usually if you wait until right after the last frost — that’s usually about May 15 — you’re going to know the extent of the damage on the plants,” Barton said. “You’ll have a better determination if the plant is beginning to green up or if it needs to be trimmed back — sometimes only parts of the plant will die off and some may survive.”
Look for signs of new growth this spring.
“If you want to assess the damage to your plants, you can gently bend a branch and see if it is still flexible. If this is the case, this means that new growth is possible, so just wait and see how it recovers,” Larsen wrote.
Barton suggested taking a small pocket knife and scraping lightly underneath the bark or surface of the twigs to see if there’s a green tinge to indicate new growth. If the plant is turning green and its branches are flexible, it’s probably going to be OK, but it will take time for the plant to recover, he said.
“If it’s hardened off and real fragile and breaks off, then it’s dead,” Barton said.
The plant may eventually shed the dry, brown needles.
“If the sight of all the rusty-looking foliage is too much to bear, you can take a broom and gently sweep over the shrubs to loosen some of the dead-looking growth,” Larsen wrote.
In some cases, only part of the plant died, and it can be pruned later this spring.
“Of course, people want it to look nice, so if you end up trimming out half of your shrubs because it’s half-dead, it might be better to remove the whole thing and start over,” Barton said. “It’s better to not just rush into removing everything until after the last frost.”
Until then, it’s important to continue watering the plants.
“In the near future, water the damaged shrubs and trees and try to not think about the fact that they look like they are dead or dying,” Larsen wrote. “With any luck at all, they will recover in time.” Unfortunately, full recovery may take several years, she said.
Barton said to water at the base of trees or shrubs. Mulch around the base also helps plants absorb water.
“As a general rule of thumb, when you get three or more days where it’s above 55 degrees, the plant is going to begin to come out of dormancy, so that’s an opportunity to go ahead and water around the base of that tree,” he said.
He said not to rely only on sprinkler systems to water trees, since they may not provide adequate water at the base.
Don’t put fertilizer on the plants at this time, Barton said.
“That’s the worst possible thing you could do,” he said. “Fertilizers will often accelerate the growth of plants, so if you apply a fertilizer right now, and then we get a real hard freeze, all of the new growth is going to freeze and die.”
It’s better to wait to fertilize until May or June, he said.
Larsen said if you cannot determine how much winter damage your trees or shrubs have, then get another opinion from an arborist or nursery in the area.
Barton encouraged residents to take their time and seek out information about their plants before determining the next course of action.
“If they ask the right questions of the right people, they can save themselves some money and time by helping the plants along,” he said.
When planting new trees and shrubs, it’s important to choose the right plants for Wyoming’s climate, which is hardiness zones 3 and 4, Barton added.
For more information about the winter damage and other tree issues, visit the Parks Department page on the city of Powell’s website at www.cityofpowell.com/assets/pages/city/parks.aspx.