While much of our state sits in a deep freeze and I am sitting in a nice warm room, I started to think about snow cover and 15 degrees temperatures Wednesday night and I asked myself, "How do plants in this climate survive these conditions and make it until spring?"
Well, the most obvious answer is mulching around the plant. This does keep the roots warmer. But it is still pretty cold under that mulch and snow, so how do perennials live to see a warmer time?
Of course, planting plants that are hardy to our zone 7b will survive much better. The USDA has created climatic zones based on the average coldest temperature for certain regions of the U.S. Gardeners can choose plants that will perform well in our area. Check the tags of the plants when you purchase them. They will usually tell you what zones a particular plant will live in.
But all perennial plants have the mechanism that allows it to return in the spring after a winter of below freezing. Many perennials lose their plant parts that are exposed as the temperatures drop before it occurs. The remaining roots in the ground move as much water in their tissues cells as possible into the surrounding ground. With less moisture in the plant's cells, a certain amount of freezing and thawing can occur without disrupting the plant cells, which could cause them to rupture.
Also, sugars and salts in the roots act as a natural antifreeze. The freezing point of the water in plants actually lowers where they can survive lower temperatures. For example, when you salt a driveway from the ice and snow, the concept works the same way in plants. Plant cells survive sub freezing temperatures by adjusting their solutes, proteins and water moisture. Talk about the perfection of mother nature!
In temperate zones on Earth, that is what perennial plants must do to be able to survive. A complete life cycle!
If exposure to cold injury occurs on the fruit, stems, leaves or trunks of a plant, it may go unnoticed until the plant fails to come of out dormancy in the spring.
Three types of cold injury can occur. The first is called a "burn." This is characterized by parts of the plant that become mushy and may turn black or brown. The damaged parts will dry out and appear to be scorched.
The second is desiccation, which is caused by winter winds. Cold air has less moisture in it and will dehydrate plants if winds persist for a long time.
The third type of cold injury is "frost crack" on leaves and stems of a plant. Water in the cells of the plants freeze just beneath the bark on a cold night and when the sun hits the areas the next day, the water thaws, quickly killing the cells and splitting the wood.
Prevention is the only method and you can begin by planting native plants acclimated to our area and zones. Provide windbreaks to block frigid winds. Cover your plants with fabric on cold nights. When planting, pick a site that maximizes evening winter sun, like a southwest side of a home. Finally, occasional watering will keep a plant hydrated from the cold air and frozen soil.
In my next article, I will begin addressing gardeners with their many questions that I receive at the Extension office and through e-mail. The format will be different and I hope to give you some interesting tidbits about gardening and also provide a monthly gardening calendar to keep you up to date on seasonal gardening practices.
If you have some questions for me, please contact me at email@example.com. I will present a Q & A on various gardening questions and topics, so get in touch! I would love to hear from you. I might publish your questions in the next article.
Thanks to the Georgia Center for Urban Agriculture and County Extension Agent Stephen D. Pettis.
Wanda Cannon is a Master Gardener trained through the Hall County program and also serves as Master Gardener coordinator and horticulture assistant for the Hall County Extension office. Phone: 770-535-8293.