Tree Commission offers winter tips

The Wauseon Tree Commission is offering the public tips on winter injury to trees and shrubs and how to minimize problems.

• The frequency and severity of winter damage is determined by several factors including the plant species, the location and condition under which the plant is grown, and the exact timing of weather extremes during the dormant period. Plant damage isn’t caused by an unusually cold winter but by extreme temperature fluctuation.

• Dormant plants not fully acclimated to temperatures much below freezing can be stressed or injured by a sudden, hard freeze. Extended periods of mild winter weather can de-acclimate plants, making them vulnerable to injury. Rapid or extensive drops in temperature following a mild autumn causes injury to woody plants.

• Some species or cultivars of trees and shrubs are injured if temperatures fall below a minimum tolerance level. Plants most likely to suffer are marginally hardy for the area or already weakened by previous stress. Rhododendron, holly, and some magnolias are among species that may survive several mild winters before being injured by a more typical one. Flower buds are often the most susceptible.

• Frost cracks appear in tree trunks as shallow to deep longitudinal cracks, and are most evident at below 15 degree Fahrenheit. They often, but not always, appear on the south or southwest sides of trees. A sudden drop in causes the outer layer of wood to contract more than the inner layer, resulting long, vertical cracks. Trees most susceptible include London plane, oak, Norway and red maple, horsechestnut, crabapple, walnut, linden, and willow.

• Sunscald is an elongated canker found on the trunk of thin-barked trees, such as beech, maple, willow, white pine, and linden. It often develops on the south or southwest side of trees following sudden exposure to direct sun. The bark darkens, turns reddish brown, and becomes rough. Affected trees often have sparse foliage, stem dieback, and stunted growth.

• Winter burn on evergreens results in browning or scorched leaf tip from the needle tips downward in late winter and early spring. Symptoms are present on many narrow-leafed evergreens, such as hemlock, juniper, pine, and yew, and on broad-leafed evergreens such as boxwood and rhododendron. It’s often attributed to a loss of water through leaf transpiration.

• Repeated freezing and thawing of soil in the fall or spring causes soil to contract and expand, called frost heaving. It damages roots and heave shrubs and new plantings out of the ground. Heaving can be prevented with a four- to six-inch layer of mulch.

• Proper pruning can eliminate snow and ice damage caused by bent and breaking branches. Trees most subject to this are multiple leader, upright evergreens such as arborvitae and juniper, and multiple leader and clump trees such as birch.

• Salt used for deicing walks and roads can cause or aggravate winter injury and dieback by injuring roots and damaging foliage through absorption.

Minimize tree damage by selecting hardy species and cultivars, avoiding late season fertilization, watering during dry periods, and using mulch to retain water and insulate roots.

Reprinted from the Morton Arboretum