Will the Cold Harm My Plants?
Most of central NC lies within USDA hardiness zone 7b, which has an expected average minimum temperature of 5 degrees. While it is rare, temperatures can fall below this expected minimum and cause damage to some landscape and garden plants.
When Is Damage Most Likely To Occur?
Many factors impact whether or not a specific plant is damaged by cold temperatures, including snow cover. Extremely cold temperatures often follow a winter storm. If the storm left behind a blanket of snow, plants are less likely to be damaged – especially low growing plants, bulbs, and dormant perennials covered by snow.
Time of the year also makes a difference. When extreme cold occurs in the early part of winter (Jan – Feb), most landscape trees and shrubs, fruit trees, and berry plants are fully dormant and unlikely to be damaged.
Later in the season (March – April), many plant parts are more susceptible to temperatures below freezing, especially flower buds. Late freezes are particularly damaging if they are preceded by a warm spell.
Plants Most Likely To Be Damaged
Plants growing in containers are exposed to colder temperatures than those rooted in the ground. Containers that can be moved should be brought into a garage or shed, or, at a minimum, pushed up against the eaves of the house. Containers too large or heavy to move can be completely surrounded and covered with several layers of insulating materials.
Trees and shrubs that are marginally hardy in our region are more at risk of cold injury, especially non-native varieties rated as hardy to zone 7b or 8. Figs and gardenias are the plants most frequently damaged by single digit temperatures in NC Piedmont landscapes.
Protecting Prized Plants
While figs and gardenias are not likely to be completely killed by cold temperatures experienced in central NC, their stems may freeze – causing all above ground parts of the plant to die back.
When this happens, new sprouts should emerge from the base of damaged plants in spring. Figs that freeze back in winter typically regrow vigorously but are not likely to ripen fruit for a season or two, while freezing back to ground level will delay flowering in gardenias.
For a prized plant, such as an heirloom fig bush or specimen gardenia, it may be worth the effort to provide extra protection.
If you wish protect an entire fig or gardenia bush, one option is to surround each bush with a cage made of chicken wire and fill it with loose, dry mulch or straw before temperatures plunge. Remove the cage as soon as temperatures rise above freezing.
Another option is to build a frame around the plant and completely cover the frame with double layers of plastic or frost protection cloth, then place a heat source underneath. Ensure the frame’s covering reaches all the way to the ground and is well secured.
Old-fashion incandescent bulbs or Christmas lights are often used as the heat source, but they have to be the older, less energy efficient types to be effective. Newer LED bulbs give off little heat – that’s part of what makes them so energy efficient.
A local gardener shared that she uses a slow cooker filled with water as a heat source to keep her covered plants just above freezing. No matter what you use, take extreme care to prevent fire and electrical malfunctions.
When spring does arrive, don’t be too quick to give up on cold damaged plants. Even if the entire top is frozen, gardenias, figs and several other woody plants will recover by sprouting from the base or roots, though it may be May or even June before new growth emerges.
Not sure of your landscape plants’ hardiness? Find out the USDA hardiness rating and much more from the N.C. Cooperative Extension Plants Database
Additional Extension Resources:
- Protecting Plants from Cold Damage, NC State Extension
- Cold Damage, Clemson Extension
- Winter Damage on Landscape Plants, Maryland Extension
- Protecting Plants from Cold Temperatures, MSU Extension
- Protect Plants from Winter Frosts, Freezes, LSU Extension
Use Extension Search to find research based information from Cooperative Extension systems across the U.S.
Visit your local Cooperative Extension center to learn more about gardening and landscape care. Find your county Extension center or post your questions to be answered online via Extension’s ‘Ask an Expert’ widget.
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