Like homeowners who still hadn’t winterized their sprinklers during last fall’s mild weather, many eastern Colorado trees were unprepared for the record-breaking cold in early November. Temperatures in Denver plunged from the high 60s to minus 14 degrees over just four days, and as a result, many trees suffered needle and bud damage that will impact tree health this year.
“Foresters along the Front Range have been getting calls on damaged evergreens in particular, with homeowners suspecting mountain pine beetle or another tree pest,” said Keith Wood, community forestry program manager for the Colorado State Forest Service. “But we believe much of the damage people are seeing now is due to the fall cold snap, or simply to dryer, colder winter weather.”
Tree damage is visible from Fort Collins to south of Denver, and from Boulder to points much farther east. In some cases, the needles on entire conifer trees are fading, and the needles of many ponderosa pines are displaying a stark white color not typically seen – which foresters believe is solely due to the fall cold snap.
Red-to-brown needles also are present on many evergreen trees and shrubs, including Scotch, Austrian and limber pines; junipers; and spruce trees, mostly on the south-facing side. This likely is due to the November cold snap as well, but may also be related to winter scorch conditions observed each year.
Additionally, many deciduous tree species were slow going into dormancy last fall, with green leaves still attached to hardwoods like pear, oak, elm and linden when the freeze hit. And some broad-leafed evergreen shrubs have been damaged.
‘Wait and see’ approach
Although homeowners may be concerned about losing damaged trees, Wood recommends that they take a “wait and see” approach. Last year’s needle growth on pines likely will fall off of these trees during this growing season, and some buds of various tree species will be inviable, so homeowners may see sparser-looking trees going into summer. But for now, Wood says providing general tree care is the best option, which means winter watering on warmer days and ensuring that mulch is present around tree bases.
“We won’t know the full impact on these trees until late spring, when their buds come out of dormancy,” he said.
Extension tree tips
“The sudden, dramatic temperature drop in early November 2014 will have lingering impacts on trees along the Front Range of Colorado,” said CSU Extension Specialist Tamla Blunt. “Evergreens prepare for winter by withdrawing moisture from pine needles. On Nov. 10, the high was 58 degrees Fahrenheit at 8 a.m., by 11 p.m. that day the temperatures had dropped to 16 degrees Fahrenheit, and fell to below zero on subsequent days. Due to the warm, lengthy fall, trees and shrubs had not completed preparation for winter, and we are seeing the freeze damage now.”
Colorado State University Plant Diagnostic Clinic has prepared an advisory, “Landscape Health Update: Cold Snap Lingering Effects” which may be found at https://plantclinic.agsci.colostate.edu/files/2014/06/Polar-vortex-bulletin-Feb-2015.pdf
CSU Extension’s Winter Watering Fact Sheet can be found at www.ext.colostate.edu/pubs/garden/07211.html