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'Wait-and-see' before assessing cold damage
MISSISSIPPI STATE -- Homeowners and growers should not overreact to potential damage to plants in home landscapes caused by extreme cold snaps, such as the one that hit Mississippi the last week of February.
"Although our temperatures dipped into the teens, plants that are hardy to zone 7 and 8 should not be affected by those temperatures," said Sonja Skelly, ornamental horticulture specialist with Mississippi State University's Extension Service. "Plants that are hardy in zone 7 can withstand temperatures of zero to 10 degrees, and those hardy for zone 8 can withstand temperatures as low as 10 to 20 degrees."
Skelly said plants still may have suffered some damage because factors other than temperature also influence plant survival. Some of those factors include plant characteristics, plant health, soil, water availability and microclimates.
"Waiting and watching is the key to assessing the damage, especially since damage may not show up immediately," she said. "Examine plants over the next few days for leaves or flowers becoming brown, black and/or mushy. Remove these as soon as you notice them to help prevent diseases from attacking the plant."
Assessing the damage to wood on trees and shrubs is a little more involved.
"Watch the plant during the spring. If leaves are not sprouting and the wood appears dead, check the layer of wood directly under the bark for discoloration. If that layer is black or brown, prune back behind the discoloration, but wait until late spring for any pruning," Skelly said. "The median date for the last freeze ranges from March 1 to 11 for the coast to April 1 to 10 in north Mississippi. Since pruning stimulates new growth, that growth would be more susceptible to cold in the next few weeks."
Fruits and roots are the least tolerant of cold injury because they have little ability to adjust or build up tolerance to colder temperatures. The horticulturist said special efforts could protect some plants from similar cold snaps in the coming weeks.
Skelly said windbreaks, such as temporary coverings, can help protect plants from injury when sudden cold fronts pass through an area. Covers that reach the ground and do not come in contact with foliage help reduce the amount of radiant heat loss.
When extremely cold temperatures are eminent, place a light bulb or other heat source (60 watts is sufficient) under the cover to provide heat. Be extremely careful when doing this as it create is a potential fire hazard. Do not let the bulb or heat source come in contact with the plant or cover. Remove the covers and/or provide ventilation during the day to allow for the release of heat trapped by solar radiation.
Soil that is well-watered will absorb more heat and will then radiate heat again from the ground helping to increase the elevated temperature around the plants. However, poorly drained soils will result in weak and shallow root systems, which are more susceptible to cold injury.
"Mulching the soil is very important. Mulch helps reduce heat loss, thus minimizing temperature fluctuations and protecting the roots of plants," Skelly said.