Though we have had relatively mild winters for a couple of years, cold damage to woody plants can sometimes be a problem here in Georgia.
Regardless of where you live in our state, recommended practices can maximize the chances of plant survival throughout the freezing months.
Woody ornamentals go through a process in the late summer and early fall called cold acclimation. Plants are preparing themselves for winter through this process. Acclimation is initiated by the cooler temps and shorter daylights that naturally occur during this time.
An important factor is local weather. If cold acclimation does not occur in a timely fashion and happens early or late in the season, the plant’s growing season will be shortened or the plant could be killed by early frosts.
Good plant selection and maintenance requirements also can affect the timing and extent of cold acclimation.
There are several types of plant damage that can occur in cold months. Cold injury can affect all parts of a plant, including fruit, leaves, roots, trunks and stems. Leaves and stems usually show damage first. Ice actually forms within the plant cells and kills the plant tissue. Leaves or stems of a plant become dark and mushy. If the plant went through a proper cold acclimation process, the plant can withstand these types of ice formation.
Windy, cold and dry conditions also can cause plant damage. The plant loses water through evaporation. This damage happens when it exceeds normal water absorption. This will cause a drying out of the plant and scorching or leaf burn will show up on the leaves.
Flower and leaf buds also can be damaged by cold, especially when temperatures are low and fluctuate. Damage to the foliage is present and you may see a reduction or total loss of blooms. If you suspect bud or bloom damage, remove several buds and open them to reveal their condition. If the buds are green throughout, they are healthy. If they show signs of browning or a darkened condition, chances are they have been damaged by cold.
Bark splitting is another form of cold damage to a woody plant. It is described as loose bark in different areas of the trunk. As this bark defoliates from the dead tissue, a canker may form. A canker usually forms as a darkened, moist area. This type of splitting can cause structural damage and may reduce the plant’s ability to transport vital nutrients and water. Several severe cankers can cause death to the entire plant.
Preventive measures to reduce cold damage are:
Select plants that can tolerate cold temperatures in your area. And also choose the proper site to plant. The north and northwest sides of a home are usually the coldest in the winter. Also, low areas can harbor cold air.
Fertilize your plants at the proper time of the year. A plant given the right nutrition is more capable of achieving cold acclimation.
For most plants, pruning just prior to early spring growth will keep most plants from being susceptible to cold damage. Pruning in late summer and early fall increases the chance of damage to new growth. Transplanted plants put in late fall or early winter also have a higher chance of winter damage. Try to transplant in early fall.
Try to establish canopies and shade areas for plants that can be grown in the shade. The shelter reduces the winter drying out and water loss. Plants that prefer full sun will not do well in shade so make sure the planting site is in the right location.
Windbreaks can be important in reducing injury to ornamentals. They can be structures such as fences, buildings and evergreen trees. Any object that can reduce the cold winds and freezes around your home can help protect a plant.
Container plants can be protected by either placing them inside a house, covered patio or garage or by placing a protective covering over them. Container plantings are especially susceptible to cold damage because their root systems are above ground. Push containers together or wrap them in burlap to decrease heat loss.
Mulching plants will also help to reduce heat loss of the soil. Covering plants with sheets, blankets or boxes helps protect them. Always remove the covering during the day for ventilation. Trapped solar radiation will heat up the environment around a covered plant during the day and cause damage.
During colder months, plants continue to have watering needs. Moist soil actually absorbs more heat, keeping the soil temperatures at an elevated temperature. Sound irrigating practices is essential for a healthy plant to be cold-hardy.
Mulching around the base of plants helps retain moisture levels.
Maximizing your chances of cold survival of your favorite and prized landscape plants is important. Use these tips and keep your plants healthy throughout the winter.
Thanks to Robert Westerfield, UGA Extension Horticulturist and Dr. Orville Lindstrom, UGA Professor of Horticulture.