Nightmare on Elm Street

The recent freeze that followed a warm spell has gardeners living with fear for their trees, roses and shrubs.

Carol O'Meara, Colorado State University Extension

Carol O’Meara, Colorado State University Extension

LONGMONT – Whenever there’s a remake of a Hollywood classic thriller, I get a bit nervous. Will it be as good as the original, or fall short of the mark? Can the remake become a hit on its own, or will it be an empty imitation of great work? And if the original was really bad, can the modern one surpass it?

The recent freeze that followed a warm spell has gardeners living with fear for their trees, roses and shrubs. We’re gathering in groups, unable to do more than whisper our worry that the boogeyman we encountered in the sudden freeze will come back, in our very own version of Nightmare on Elm Street.

Only in our case, it’s the Nightmare on Elm, Willow, Juniper and Fruit Tree Street.  Unusual autumn warmth was back, giving us temperatures better suited to August. And like the doomed victims in horror movies, those darned plants didn’t pay attention to our warnings and harden off for winter. Instead, trees and shrubs held onto green leaves and shoots, eager to keep summer going.

The polar vortex in November, 2014, was a plummeting of temperatures from near 60 degrees to 16 degrees in 15 hours, flash freezing plants. This year, temperatures dropped from a balmy 63 degrees to 16 degrees in 36 hours. There is little we can do to stop the damage of extreme temperature drop, but gardeners do have a few things they can do to help the plants afterwards.

To get ready for winter, plants undergo a two-stage process of dormancy and chilling. Called “cold hardening,” it enables woody plants to withstand winter weather. As days shorten, deciduous woody plants undergo resorbing, which converts leaf starch, proteins and other complex molecules into soluble molecules, such as sugars and amino acids, moving them into storage cells in the inner bark of twigs, the outer sapwood of the main stem, and in roots.

In spring, the stored nutrients are used for the flush of new leaves and burst of growth in shoots and roots. In fall, once resorption is complete, woody plants form a layer between the branch and the leaf petiole to close off pathways from stem to leaf, allowing the leaf to fall.

Gradually freezing temperatures ensure the plant is cold hardy for the remainder of winter. This fall, we’ve had some gradual cooling and light freezes. This triggered trees to form the barrier between leaf and stem, a precursor to allowing the leaf to drop. The hard freeze and heavy snow stripped the leaves from the tree in one swoop, causing the entire tree to denude itself in one day.

Although it means I’ll power through raking, the tree should be fine. But thin barked trees should be watched for signs of bark splitting from the freeze, and wrapping for winter to prevent any further damage.  Sun hitting trunks on south and west sides warms the bark and cells underneath, causing them to lose their cold protection. As nighttime temperatures plunge, these cells freeze and burst, resulting in sunscald on the trunk, an area that will be prone to disease in summer.

Sapling fruit trees are vulnerable to sunscald, as well as lindens, honeylocusts, ashes, oaks, maples, and willows. Protect them for the first two to three years they’re in your landscape by wrapping them with tree wrap in early in November.

Wrap from the ground upward, overlapping each layer over the lower one by one-half-inch until you reach the lowest branch. Use tape to hold the wrap in place, making sure the tape doesn’t stick to the trunk.

Researchers at Colorado State University recommend that all landscape areas should be watered thoroughly in late fall, then once monthly until spring if we have little snow. This monthly watering is important to tree health.

By Carol O’Meara. Colorado State University Extension, together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and 4-H youth development. For more information contact Colorado State University Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, e-mail comeara@bouldercounty.org or
visit ext.colostate.edu/boulder.