Q: One of my plants was killed by the cold weather. I thought it was hardy. May I take it back for a refund?
A: Cold hardiness is not an exact science, and there are numerous factors that come into play when considering how cold hardy a plant is. A plant may survive 0 degrees Fahrenheit for one night with no damage provided temperatures rise the next day. The same plant may be killed outright if exposed to only 15 degrees for three nights if daytime temperatures don’t rise above freezing.
Plants that are well-established are less likely to be damaged than those planted more recently. Cold snaps that follow extremely warm periods are more damaging than those that come after a gradual period of cooling. Plants that are flushed with new growth due to lots of water and nitrogen fertilizer are also more likely to be damaged than those grown under leaner conditions. Plants in pots and containers are much more susceptible to cold damage because their roots are more exposed than those of plants in the ground. Some plants will survive low temperatures provided their roots are not wet but will die during cold, damp periods.
Some evergreen shrubs in sunny areas will experience “leaf burn” if the ground remains frozen for extended periods. This is because the sunlight will raise the temperature of the leaf and cause it to transpire and lose water. The plant is unable to absorb water from the frozen ground which leads to the scorched appearance of the leaves. These plants often re-leaf in the spring with no major damage. When you see this kind of damage, don’t jump to a premature conclusion that the plant is dead.
Are your sure your plant was supposed to survive the winter? Also, don’t forget that many perennials die back to the ground but re-sprout in the spring. They are not dead but may look like it on the surface.
It is unfair to expect a nursery to predict every possible scenario and guarantee success in all situations and conditions. If we are that demanding, it may lead to nurseries carrying only weedy plants like Chinese privet and Japanese honeysuckle that will grow practically anywhere.
Q: It looks like the cold has killed or extremely damaged my trailing rosemary, pittosporum, creeping fig, sago palm and some other evergreen plants. When should I prune them back or pull them up? Why is there so much damage this year?
A: Have patience! Many evergreen plants such as the ones you mentioned may have dead or damaged leaves but will re-sprout from the stems. Wait until late spring before cutting them back. When the plants begin growing, you can better determine the extent of the damage and what you need to do.
Even though the fronds of sago palm may be completely dead, do not cut them off now. They may help protect the trunk from further damage during the rest of the winter. Also, a half-brown or half-damaged frond on any palm should be left until new fronds arise because the living half is continuing to manufacture food for the plant.
Having said that, sago palm, creeping fig and other plants that are truly only marginally hardy in north Georgia have been overwintering outdoors with few problems in recent years due to mild winters. It has been a while since we experienced the extremely low temperatures we had for extended periods this winter. Some of these marginally hardy plants will survive and some will not. However, we still need to wait and see before we pull out the pruners, handsaw or shovel.
Sunny conditions during or immediately following periods of extreme cold are especially damaging for evergreen plants. The low temperatures freeze the soil and the moisture in it; when the sun comes out it heats the surface of the leaves and causes them to begin losing water due to transpiration. That is why leaves damaged by the cold may look scorched as if they were burned in a summer drought. Many areas experienced this. Wind, in addition to the sunshine, will further exacerbate the water loss and subsequent damage.
Snow can be a plant’s best friend during cold weather. Snow can insulate the ground and the plants themselves against further dips in temperature and protect leaves and stems from the loss of water due to transpiration.
Q: It is five degrees outside. Some of my evergreens and other plants look so terrible I could cry. Has the cold killed them?
A: Many evergreens, especially broad-leaved evergreens such as camellias, English ivy, Algerian ivy, cast iron plant and rohdeas will turn a much darker color during extremely low temperatures and can look like they have been dipped in boiling water. The leaves on rhododendrons will even roll up like tubes. They will go back to their normal appearance when temperatures rise, probably with no damage.
That being said, plants that are marginally hardy in much of the state such as sago palm, spike dracaena and creeping fig may have done well during recent mild winters but can be damaged or killed by temperatures in the single digits. However, don’t start cutting them down or digging them up. Wait until spring to see if they sprout back. Even an evergreen plant that lost all its leaves may sprout back from the stem or base.
Milk-and-wine lilies and other crinums and amarcrinums usually keep a few green leaves at the top until a severe freeze. Now those leaves will look dead and mushy. Leave them alone. They will probably be fine and re-sprout in late spring.
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