How To Keep Your Plants Warm During The Winter

Winter in the South can be hard on plants. Fluctuating temperatures, sporadic freezes, and winter winds all take their toll on the garden. Some plants need a little extra protection to make it through cold snaps. Don’t wait until the weatherman predicts a freeze. Learn how to keep plants warm in winter and take steps now to prepare your garden.

Why Plants Need Protection

Winter is a rest period for the garden. Many plants go dormant, with their tops dying back and all their energy stored safely below ground. However, not all dormant plants are safe from cold damage. Some plants with very shallow roots, such as heuchera, astilbe, gaillardia, and strawberry, can be damaged by heaving or uplift of soils caused by freeze-thaw cycles. Heaving can literally lift shallow-rooted plants out of the ground, exposing the tender crowns to freezing temperatures.

Other plants weather the cold above ground. Broadleaf evergreens, those staples of Southern gardens, are particularly sensitive to water loss during winter, while young, thin-barked trees such as maples are commonly damaged by alternating periods of freezing and thawing. Even well adapted plants can suffer damage if they enter the winter stressed by drought. With a little planning, you can help plants withstand all these types of winter damage.

Protecting Plant Roots

Winter garden protection begins with caring for the life force of plants–their roots. Provide plant roots with a warm winter blanket of mulch. A two- to four-inch mulch layer around trees, shrubs and perennial beds helps reduce moisture loss and moderates soil temperatures during the winter months. Mulch also reduces problems with heaving soils. While wood chips are always a great choice for mulch, light-weight materials such as chopped leaves, pine needles, and straw are ideal for winter because they don’t compact. This is a great way to use all those autumn leaves littering the lawn. Be sure to leave a 6-inch ring free of mulch around the trunks of trees and shrubs to prevent pest problems. 

Watering 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 during the winter when high winds or periods of warm weather cause evaporation from foliage. If this water loss occurs at times when the ground is frozen, roots cannot take up moisture to replace lost water. The result is browning or burning of the foliage.

To protect plants roots and provide evergreens with adequate moisture, monitor weather conditions and water during extended dry periods or about one to two times per month. Water only when air temperatures are above 40˚ F and apply water at mid-day so it will have time to soak in before possible freezing at night. Irrigate all plantings at least 24 hours before hard-freezing weather if the soil is dry. Make sure plants enter the dormant season in a healthy and vigorous condition. Proper irrigation during autumn will help prepare landscape plants for the coming winter. 

Choosing Cold-Tolerant Plants

As they say in football, the best defense is a good offense. For plants, that means selecting plants that can tolerate cold temperatures and freezing weather, so you don’t need to protect them. When you purchase plants, look for the USDA hardiness zone rating on plant labels or catalog descriptions and avoid plants that are not hardy in your zone. For container plants, select species that are hardy to two zones colder than your area to ensure winter survival. You also want to make sure plants can tolerate summer heat typical of your area.

Insulating Techniques

Despite our best efforts to select plants adapted to our local climate, temperatures sometimes fall outside the average. Of course, we gardeners also like to push the limits, experimenting with plant material that is marginally hardy for our region. Pay attention to the weather report and know the limits of sensitive plants in your garden.  

When freezing temperatures threaten, we can take steps to insulate plants against the cold. For brief freezes, you can simply cover plants with blankets, towels, burlap, or other insulating materials. Make sure to weigh the edges of the covering down to the ground. Lift coverings during the day to prevent excess heat build up from the sun. Remove insulating materials as soon as temperatures allow. 

Young trees and those with thin bark, like maples and many fruit trees, are sensitive to alternating periods of freezing and thawing which cause cracks to form as the bark swells and contracts. Susceptible trees benefit from a protective paper or plastic wrap during the winter months for the first two growing seasons. Remove warps in early spring prior to spring growth to avoid damaging the trunk.   

Providing Heat Sources

For severe freezes, you may wish to provide a source of heat beneath covers to further warm plants. The safest way to do this is to use a heat sink such as a jug filled with hot water or stones warmed in the sun. These materials slowly release heat during the night, keeping temperatures beneath insulation blankets a few degrees warmer.  

Lights can also be placed beneath covers to provide heat. While some homeowners use 60-watt bulbs, these can be a fire hazard if they touch the plant cover. A safer alternative is to use strings of outdoor Christmas lights (not LED’s, which do not produce heat). The lights provide additional heat without getting hot enough to burn plants or plant covers. Remove covers during the day to provide ventilation and prevent excess heat build up due to solar gain. 

Creating A Microclimate

A microclimate is an area of the landscape that has slightly different conditions than the larger landscape. You can take advantage of microclimates to site sensitive plants. For example, a south or west-facing brick or stone wall gathers heat from the sun and slowly releases it throughout the night, keeping the surrounding area slightly warmer. The same is true of some patios. Likewise, trees and other canopies help reduce radiant heat loss from plants and soil, providing a layer of protection to plants below.  

Boxwoods and other broadleaf evergreens benefit from winter wind protection. 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 stakes or over a lattice frame.

Conclusion

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. Be familiar with the plants in your landscape and identify which ones might need extra protection during a cold snap. Be ready for those freezes by keeping a pile of blankets on hand.