Unseasonably warm weather has gardeners on edge about negative effects

Published 12:00 am Friday, January 5, 2007

Normally ice and snow would be a major topic of discussion in January, however, unseasonable weather has many gardeners concerned about the negative effect on plant growth. Unseasonably warm weather has its benefits; however, in horticulture it may spell disaster.

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 40 degrees to properly break dormancy. The leaf buds need even more chilling hours, closer to 1,000 hours. Unseasonably warm weather can cause the tree to bloom but have few leaves.

Unseasonably warm weather during winter or early spring can also be a detriment to landscape plant material. Plant materials are often damaged when unseasonably warm weather stimulates the 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.

Ornamental plums and some magnolias were in full bloom over the Christmas holidays. My daphne odora is laden with swollen buds ready to open –about a month or so early.

Cold injury symptoms on plant materials are manifested as 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. Small limbs or twigs often have lateral splits causing the plant to have splotches of dead foliage.

What do we do to protect our plants from cold damage? Trees and shrubs can be protected from winter damage with an application of organic mulch. Now is a good time to apply mulch. Six to 8 inches of coarse wood chips, bark or pine straw over the root zone helps retain soil moisture and maintains a constant soil temperature around the root system.

The scenario for both homeowners and growers is a gradual cooling trend with a return to normal winter temperatures.


Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension in Rowan County. Visit the Cooperative Extension Web site at http://rowan.ces.state. nc.us.