This is the time of year when, with all but the hardiest plants sheltered for the winter, most gardeners kick back with their seed catalogs and start planning for the coming planting season. However, even the hardiest plants might need a little extra protection during the severe freezes these winter months can bring.
A severe freeze is defined as when the air temperature is 24 degrees Fahrenheit or lower. It’s at these frigid temperatures that any plant left outdoors can easily be damaged, particularly the more delicate ones that are either newly planted and not entirely established, as well as those that are not entirely cold-tolerant.
Thankfully, we are (mostly) eased into this bitter cold weather starting in the fall, with lighter freezes (28 to 32 degrees Fahrenheit) giving way to more moderate freezes (24 to 28 degrees Fahrenheit), as the seasons shift from the warmth of summer to the cooler autumn and finally, the cold of winter. This progression of weather allows plants to adjust to the cooler months, which helps prevent the damage done by a sudden drop in temperatures that take plants by surprise—although if it’s cold enough, almost nothing will escape damage. According to Tim Quillen, landscape manager of Waynesboro Nurseries, hollies will drop their leaves and evergreens their needles if it’s cold enough. Dan Gregg of Grelen Nursery, Inc. concurs, adding that broad-leaf evergreens are most susceptible to cold damage when the thermometer takes a sudden nose dive.
The most vulnerable plants are ones most recently planted—in particular, those planted the previous fall. Gregg recommends keeping those plants watered, taking care not to flood the frozen ground. Wet soil holds heat better than dry soil, keeping the air around the plant warmer, thus protecting the plant. In addition to keeping plants irrigated, giving them an added layer of protection during especially cold blasts can help protect them. This can be done in various ways, as there are different methods of winter weather protection for different plants. Quillen tells of gardeners who build structures out of plywood and wooden stakes over small bushes, to protect delicate boxwoods from becoming squashed by heavy snow and ice, the weight of which can snap branches. Other methods include wrapping plants in burlap or insulating them in a method known as “pine tags”—the practice of wrapping wire fencing around a plant, then stuffing the space with pine needles. Gregg warns about using pine tags for too long of a period, as the cozy coverage for plants can be irresistible to rodents looking for protection from the elements. Both Gregg and Quillen recommend covering susceptible plants with burlap when the thermometer heads to the deep south, then stuffing straw in the gaps between the plant and the burlap, taking care to not break the limbs of the plant. The straw acts as an insulator, while the burlap allows the plant to breathe, letting moisture escape, but preventing the cold air from touching the escaping moisture and damaging the plant. Take care to drape the burlap to the ground, which helps protect the entire plant. When the cold snap ends, remove the burlap and straw. While there are anti-transpirants that can be sprayed on plants to seal in moisture and protect them against cold, Gregg doesn’t recommend using these, as they also don’t allow plants to give off moisture, which can lead to other problems.
The most delicate plants in our area—in addition to anything planted recently this past fall—are camellias, gardenias, figs and crepe myrtles. All but the crepe myrtle tend to die back to the ground in severe freezes, while their roots, protected by the soil, stay alive. Come the warmth of spring, they’ll push out new growth at the ground level, essentially starting over for the plant—which can be heartbreaking to a gardener, particularly when the plant in question is established and of a good size. Because figs need to be able to grow on the previous year’s growth to produce fruit, Quillen recommends making the effort to save them, particularly when the temperature goes below 20 degrees Fahrenheit. Depending upon the height of the crepe myrtle, it might not die back to the ground but just experience some damage to the top. A good pruning in spring to remove the dead growth will help your trees bounce back.
What about those plants you keep in pots year round? While some plants might be able to weather the cold temperatures in pots, not all can. It depends on how much room the roots have in the pots: the larger the roots, the closer they will be to the walls of the pot and more susceptible to damage. When the roots are smaller, allowing for more soil to stand between them and the pot they call home, the better off the plants will be. The amount of moisture in the pot is also a factor; as the temperature drops, the moisture freezes and expands, which can crack or even break your pots, particularly clay ones. Making sure any pots you leave out all winter drain well is key to having them last another season. To be most cautious, move any potted plants into an area where they can be protected—a garage or basement—during severe cold blasts. This will ensure they stay in good health while your pots will remain in good repair.
Plants are incredibly resilient living beings. Quillen recommends that if you have a tree or bush planted in a prominent spot in your yard, you’ll want to take care to preserve it in extreme weather. Most plants will survive whatever Mother Nature throws at them, so even if they see some damage, they should be okay in the long run. In the case of damage, wait until the weather warms up before pruning or taking any other action. When you see new growth at the base of the plant, that’s the time to prune it back. If there are no signs of life, that is when you’ll know winter got the best of your plant. Thankfully, there’s always next year.