Many Front Range trees and shrubs are not leafing well, leafing slowly or appear to be dead. A number of these were injured by the severe cold snap last October 8-9, 2009. The damaged plants had not fully “hardened off” when temperatures took their sudden drop. (Hardening off is a natural, gradual process that prepares woody plants to survive cold winter temperatures.)
In some cases, affected plants were already stressed by environmental conditions and predisposed to further damage from the cold. Numerous ash were already struggling with “ash decline” or borers. Some catalpas had verticillium wilt, a fungal disease that attacks conductive tissue and weakens plants.
Trees and shrubs that received late summer or early fall irrigation and nitrogen fertilizer remained succulent rather than hardening off and were more prone to cold injury.
A significant amount of dieback has been observed on rose, spirea, blue mist spirea, honeylocust, crabapple, ash, Amur maple, red oak, catalpa, hackberry and others. Some trees with dead tops are just now pushing shoot growth from latent buds in the trunk. Any trees showing this type of growth will generally not develop into strong landscape trees and should probably be removed.
For more information, call the Jefferson County, CSU Extension at 303-271-6620.