Garden Column for the Salisbury Post

Darrell Blackwelder

January 5, 2005

I was asked a number of horticultural questions over the past few days pertaining to our unseasonable warm weather. Normally ice and snow would be a major topic of discussion, however, unseasonable weather has some concerned about the negative effect on plant growth.

One of the most prevalent inquiries is will the warm weather affect the fruit crops.  A cautious answer is maybe. Unseasonably warm temperatures in the winter can cause problems with certain tree fruit cultivars. Fruit trees, especially peach and apple, need a certain number of cold hours to initiate bloom set. Peach cultivars, such as Elberta, need between 700-800 hours of temperatures below to properly break dormancy. The leaf buds need even more chilling hours, closer to 1000 hours. Unseasonably warm weather can cause the tree to bloom but have few leaves. This is a typical a problem with unseasonable warm winters.        Unseasonably warm weather during winter or early spring is also a major problem to landscape plant material. Landscape plant material is often damaged when unseasonably warm weather during winter stimulates the production of new growth. It’s inevitable that Rowan County will experience more cold weather in a few weeks.  Variable weather patterns do more than confuse plants; sudden cold snaps can be very damaging to tender foliage, especially on newly planted trees and shrubs.

Cold injury symptoms on plant materials usually show up as a blackening or browning of certain areas of the plant. Damage is not always immediate and it typically doesn’t appear until a week or more after the cold weather has occurred. In some instances, such as cold damage on azaleas, damage may not be evident until late spring or early summer.                                       

What do we do to protect our plants from cold damage?  Irrigating trees and shrubs is very important to the survival when freezing weather returns. Make sure that plants are irrigated deeply just before the ground freezes.       Irrigation is especially vital for evergreen trees and shrubs because they transpire moisture all winter long. Adequate soil moisture also serves as a buffer against very low soil temperatures by holding more heat in the soil.  .          Trees and shrubs can also be protected from winter damage with an application of organic mulch. Now is a good time to apply mulch. Six to eight inches of coarse wood chips, bark or pine straw over the root zone helps retain soil moisture also maintains a constant soil temperature around the root system.

Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener web site at www.rowanmastergardener.com , e-mail Darrell_Blackwelder@ncsu.edu