As you may have noticed, there are a lot of dead shrubs, and trees out there this Spring. And others look just plain puny. What happened?! We here at Panorama like to call it the “Polar Vortex.” It happened on November 10, 2014, and the impact of this event could last for years. On November 10, 2014, we had a high temperature of 64 degrees recorded at the Denver, CO weather station. On the night of November 12, the record low temperature was -13 degrees. This represents a 77 degree change in temperature! This, by the way, is the 3rd largest temperature drop ever recorded in Denver since 1872. Compounding this freeze, the area was having one of its warmest falls on record, further catching landscapes off guard.
As days get shorter and temperatures cool landscapes prepare themselves for winter. A process called resorbing converts leaf starch, proteins, and other complex molecules into soluble molecules, such as sugars and amino acids. The soluble molecules are stored in cells of the inner bark of twigs and the outer sapwood of larger stems, trunk, and root tissues. Next, abscission layers are formed between the branch and the leaf petiole allowing the leaf to fall. The winter prep processes were not complete and the plant cells of trees and shrubs simply froze, and the vascular tissue burst.
Conifers showed immediate damage. Pine foliage flash froze and turned a silver color. Spruce defoliated, primarily on the south sides of the tree. Many deciduous trees and shrubs froze with their leaves still attached. This spring, Arborvitae and Boxwoods dessicated and turned brown. Burning bush, leaves still on their stems, remain lifeless. Buckthorns, always reliably hardy, froze and died. Weakened Austiran and Ponderosa pines showed little signs of new growth and older needles turned brown. Many ash, maple, and elm have severe dieback.
What can you expect going forward? Sadly, these weakened trees and shrubs are going to be more prone to pests and disease. Some trees and shrubs will make a full recovery, but that recovery may not be complete for several years. Hard pruning may help some varieties – such as dogwoods and Viburnums -this can be done now or in the fall. Enlisting the expertise of a knowledgeable landscape company and/or an arborist will give you individual property assessment and allow you to make the best decisions for your landscape. The information provided here was largely taken from an article in Rocky Mountain Arborist – the full text may be read here: https://gallery.mailchimp.com/60a9e4f49fbf28da9cd01000b/files/Rocky_Mountain_Arborist_July_2015.pdf