How Winter Affects Plants in Georgia

BY HEATHER N. KOLICH

This season, winter has tossed Georgia some unusual surprises – an October freeze and a number of balmy December days, followed by several consecutive days of subfreezing temperatures. These conditions can affect the development of fruit crops, including blueberries and peaches — crops that are economically important to our state.

From apples to strawberries, perennial fruits and nuts need a certain number of cold hours, called chill hours or chilling hours, during the winter to convince them to break dormancy for fruiting. The number of required chill hours varies by the type of fruit as well as by the different cultivars within a fruit species. For example, citrus fruits require 0-100 chill hours to produce fruit. An apple cultivar with a low chilling hours requirement, such as Anna, will begin budding with as little as 200 hours, but an apple variety requiring a high number of chilling hours, such as Honeycrisp, will remain dormant until it has accumulated 8001,000 hours of temperatures between 32 and 45 degrees.

If the planting area does not accumulate the requisite number of chilling hours between October and the end of February, fruit plants produce fewer blossoms, resulting in a lower yield. Alternatively, if the area receives too much chilling, the plants might break bud before winter ends. That is one reason oranges are grown in Florida, and apples and blueberries are grown from Georgia to Michigan.

Subfreezing temperatures, especially when prolonged, can injure or kill fruit buds. Although chill hours historically are counted at temperatures between 32 and 45 degrees, the deep-freeze weekend in December could be beneficial to Georgia’s peach and grape crops by adding chill hours, according to UGA Cooperative Extension fruit specialist Phil Brannen. Extreme cold also helps kill the bacteria that causes Pierce’s disease in grapes, as well as the pest insect that spreads the disease.

The killing cold also benefited south Georgia, where cotton, corn and peanuts are major economic crops. According to Bob Kemerait, UGA professor and extension specialist in plant pathology, the extreme cold contributed to the control of several crop pests, including rust fungi, root-feeding nematodes and kudzu.

On the home landscape front, many plants are showing signs of cold injury. Time and patience are the best treatment now, as temperatures return to normal for bedding plants, woody perennials and turfgrasses. Wait and see is the advice from UGA Extension horticulture and turfgrass specialists Bodie Pennisi and Clint Waltz.

Pansies and violas planted in beds have a good chance of recovering, but other seasonal color plants, including perennials like heuchera and dusty miller, might not prove as hardy. Plants in containers and raised beds might not recover either, as the roots were more exposed to freezing than those in the ground. Turfgrasses are likely to recover, according to Waltz. Recovery is evidence of green tissue, but don’t apply fertilizer until plants begin active growth.

Perennial shrubs and trees also were affected, especially young twigs at the edges of the canopy. Resist pruning until closer to spring, when the damage can be assessed. Pennisi said the damaged twigs could provide protection to the rest of the plant if we have another freeze event.

The Master Gardener Volunteers of Cobb County supports the University of Georgia Cooperative Extension Service and strives to improve the quality of life in our community by delivering research-based horticultural information, educational programs and projects.