Winter in the south can be harsh on plants. Fluctuating temperatures, sporadic frost and winter winds put a strain on the garden. Some plants need a little extra protection to survive cold snaps. Don't wait until the weather forecast predicts a frost. Learn how to keep plants warm in winter and take steps now to prepare your garden.
Why plants need protection
Winter is a resting time for the garden. Many plants go dormant, their tops die off and all their energy is safely stored underground. However, not all dormant plants are safe from cold damage. Some plants with very shallow roots, such as Plants such as Heuchera, Astilbe, Gaillardia and Strawberry can be damaged by heaving or lifting of the ground due to freeze-thaw cycles. Lifting can literally lift shallow-rooted plants out of the ground, exposing the delicate crowns to freezing temperatures.
Other plants survive the cold above ground. Evergreen deciduous trees, the staples of southern gardens, are particularly sensitive to water loss in winter, while young, thin-barked trees like maples are often damaged by alternating periods of freeze and thaw. Even well-adapted plants can suffer damage if they enter the winter stressed by drought. With a little planning, you can help your plants withstand all that winter damage.
Related: 15 Hardy Vegetables to Plant and Grow in Winter
Protect plant roots
Protecting winter gardens begins with caring for the life force of the plants – their roots. Provide the plant roots with a warm winter blanket of mulch. A 2- to 4-inch layer of mulch around trees, shrubs, and herbaceous beds will help reduce moisture loss and moderate soil temperatures during the winter months. Mulch also reduces disturbed soil problems. While wood chips are always a good choice for mulch, lightweight materials like chopped leaves, pine needles, and straw are ideal for winter because they don't compact. This is a great way to take advantage of all the fall leaves scattered across the lawn. Be sure to leave a 6-inch ring free of mulch around the trunks of trees and shrubs to prevent pest problems.
Irrigation and moisture management
Managing soil moisture is also an important part of protecting plant roots as well as broadleaf evergreens such as hollies, camellias and boxwoods. These plants can experience water stress in the winter when strong winds or warm weather periods cause evaporation from the foliage. If this water loss occurs during times when the ground is frozen, the roots cannot absorb moisture to replace the lost water. The result is browning or burning of the leaves.
To protect plant roots and provide adequate moisture to evergreens, monitor weather conditions and water during extended dry periods or about once or twice a month. Water only when the air temperature is above 40°F, and add the water at midday so it has time to soak before it potentially freezes at night. Water all plantings at least 24 hours before hard frost when the soil is dry. Make sure the plants enter the dormant phase in a healthy and vigorous state. Proper watering in the fall helps prepare landscape plants for the coming winter.
Choosing cold-tolerant plants
As they say in football: the best defense is a good attack. For plants, this means choosing plants that can tolerate cold temperatures and frost so you don't have to protect them. When purchasing plants, pay attention to the USDA hardiness zone classification on plant labels or catalog descriptions and avoid plants that are not hardy in your zone. For container plants, select species that are two zones colder than your region to ensure winter survival. You also want to make sure the plants can tolerate the summer heat typical of your region.
Insulation techniques
Although we make every effort to select plants adapted to our local climate, temperatures are sometimes above average. Of course, we gardeners also like to push the limits and experiment with plant material that is only partially hardy for our region. Pay attention to the weather forecast and know the limits of sensitive plants in your garden.
When freezing temperatures threaten, we can take steps to insulate plants from the cold. If there is a short-term frost, you can simply cover the plants with blankets, towels, burlap or other insulating materials. Be sure to weigh the edges of the cover down to the ground. Raise covers during the day to prevent excessive heat buildup from the sun. Remove insulation materials as soon as temperatures permit.
Young trees and those with thin bark, such as maples and many fruit trees, are sensitive to alternating periods of freeze and thaw, causing cracks to form as the bark swells and contracts. Susceptible trees benefit from protective paper or plastic wrap during the first two growing seasons in the winter months. Remove warps in early spring before spring growth to avoid damaging the trunk.
Related: The Best Plants to Overwinter, According to an Expert
Provision of heat sources
During severe frosts, you may want to provide a heat source under the cover to provide additional warmth to the plants. The safest way to do this is with a heat sink, such as a jug filled with hot water or stones heated in the sun. These materials slowly release heat at night, keeping temperatures several degrees higher under insulating blankets.
Lights can also be placed under covers to provide warmth. While some homeowners use 60-watt light bulbs, these can pose a fire hazard if they touch the plant cover. A safer alternative is to use outdoor Christmas lights (not LEDs, which don't produce heat). The lights provide additional warmth without getting so hot that they burn plants or plant coverings. During the day, remove covers to provide ventilation and prevent excessive heat buildup from sunlight.
Create a microclimate
A microclimate is an area of the landscape that has slightly different conditions than the larger landscape. You can take advantage of the microclimate to plant sensitive plants. For example, a south or west facing brick or stone wall collects the sun's heat and releases it slowly throughout the night, keeping the area slightly warmer. The same applies to some terraces. Likewise, trees and other canopies help reduce radiant heat loss from plants and soil and provide a layer of protection for the plants below.
Boxwoods and other evergreen deciduous trees benefit from wind protection in winter. You can find an ideal microclimate for these plants by placing them near hedges, fences, or other windbreaks. Or build a temporary windbreak by stretching burlap between two poles or over a trellis frame.
When it comes to keeping plants warm this winter, a little preparation can go a long way. Give plants a layer of protection by mulching and watering as needed. Familiarize yourself with the plants in your landscape and determine which ones might need extra protection during a cold snap. Be prepared for frost by keeping a stack of blankets ready.
Related: 7 Tips for Bringing Outdoor Plants Indoors for the Winter
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