Berks County Cooperative Extension -

TREES AND SHRUBS

Adapting to temperature change.

Fall is the time to consider how winter weather may affect trees and shrubs. In the fall, trees and shrubs begin a natural process to adapt to cooler temperatures. This process allows trees and shrubs to ultimately withstand harsh winter conditions. Trees and shrubs do not adapt to cold temperatures overnight, so that a prolonged period of mild temperatures in the fall, followed by the abrupt onset of very cold temperatures may cause tissue damage. It should be noted that even ideal conditions for adapting to cold temperatures do not guarantee survival; an unusually frigid winter will result in the demise of some trees and shrubs. In late winter and early spring, trees and shrubs undergo a reverse process to prepare for milder temperatures. During these periods, wide, sudden temperature fluctuations may interfere with the adaptation process, resulting in injury or death.

Moisture loss from evaporation.

When winter weather turns temporarily mild, water evaporates from the leaves and stems of trees and shrubs. If the ground is cold or frozen, roots may be unable to take up water to replace the moisture lost to evaporation. The moisture deficit causes browning of needles on evergreens and may cause significant damage to recently transplanted trees and shrubs, which have not had sufficient time to develop strong root systems.

Winter sun damage.

While most people appreciate seeing the sun in winter, trees and shrubs, especially those facing the south or southwest, do not. Sudden swings in winter temperatures and the sun may damage trees and shrubs. During the day, the sun may cause needles or branches to thaw. After the sun withdraws, the needles and branches may freeze quickly and suffer tissue damage. Results of this rapid thaw-freeze cycle (referred to as "sunscald") include browning of evergreen needles and splitting of bark on vulnerable trees such as ash, crabapple and maple.

Winter survival tips for trees and shrubs.

Aside from talking about the weather, what can one do to help trees and shrubs survive the harsh winters experienced in Berks County? Some suggestions:

Don't neglect to provide water to trees and shrubs if precipitation has been insufficient. During dry periods, continue to water young trees and shrubs until the ground freezes. When the ground thaws in the spring, resume watering if dry conditions prevail.
A layer of mulch around trees and shrubs will afford some protection against damage caused by freeze-thaw cycles. When applying mulch for this purpose, put aside some mulch during the warm months, and apply it after the ground has frozen. To prevent fungal or other damage, take care to avoid placing the mulch in contact with the trunk.
Exercise restraint in fall and spring pruning. Pruning branches with brown needles in the fall may cause buds to develop. These buds may not have enough time to harden before winter sets in. In the spring, branches may be in the process of setting new buds.

Source: Home Gardener Headlines (Berks County), Fall 1998
Document created: 15 December 1999, Revised: 18 February 2001