Although snow and ice can transform Ohio into a winter wonderland, this same snow and ice can threaten the very trees and plants they adorn.
Winter injury may be recognized as excessive browning of evergreen foliage, death of roots, bark splitting or injury or death of flower buds. Winter sun, wind and cold temperatures can bleach and desiccate evergreen foliage, damage bark and injure or kill branches. Salt, used to remove ice from streets, sidewalks and driveways, is harmful to landscape plantings. The shortage of natural food supply that occurs in the winter months can force rodents, deer and other animals to feast on bark, foliage, buds and roots. Snow and ice often breaks branches, and on occasion can topple an entire tree.
All is not lost. There are ways to protect our precious landscape plantings.
First of all, it is important to choose hardy plants for the Ohio landscape that can withstand cold temperatures. In central Ohio, we are in the USDA’s Revised Hardiness Zone 6a. Generally, these plants can withstand temperatures of 10 to 15 degrees below zero. The USDA Revised Hardiness Zones Ohio map can be viewed at ohioline.osu.edu/hyg-fact/1000/pdf/1648.pdf. Be sure to check the plant label or ask the nursery about suitability to zone 5b.
Healthy plants acclimate to colder temperatures. For many species, the shortened hours of daylight in late summer initiates the hardening process by slowing vegetative growth. The amount of nitrogen fertilizers applied should be reduced after mid-July and stopped by late summer. Ideally, plants should enter the winter season as healthy as possible but not rapidly growing. Cool temperatures also contribute to cold hardiness, particularly freezing temperatures. Gardeners can assist the cold hardiness process by watering plants late in the growing season thus decreasing the likelihood of tissue desiccation, which is one of the most common forms of winter injury, particularly in evergreens.
Another winter hazard is sun scald, which is characterized by elongated, sunken, dried, or cracked areas of dead bark typically found on the south or southwest side of a tree. On colder days, the sun heats up the bark to the point where cambial activity is stimulated. Later, the sun is blocked by a cloud, hill or building and bark temperature drops rapidly, killing active tissue. Young trees are particularly susceptible. Sun scald can be prevented by wrapping the trunk with a commercial tree wrap or plastic tree guard.
There are several other ways to protect plants in the landscape including mulching, tying, anti-desiccants, and wrapping. Mulch maintains more even soil temperatures and helps retain soil moisture. Gardeners should apply a 2 to 2.5 inch layer of mulch after the soil freezes to keep the soil cold. This practice reduces injury from plant roots heaving caused by alternate freezing and thawing. Bark products, composts, peat moss, pine needles, straw, hay and even discarded Christmas trees make ideal mulching materials.
Multiple branched plants such as junipers and yews may be damaged by the weight of snow and/or ice. Fastening heavy twine at the base of the plants and winding it around and upward to the top and back again can help protect against breakage.
Winter cold and winds cause excessive transpiration (foliage water loss) at a time when roots are in frozen soil and unable to replace lost water. This causes desiccation and browning of the plant tissue. Applying an anti-desiccant in December and February reduces the threat of injury. Wraps of burlap or canvas can also protect against desiccation from sun, wind and salt. It is important to leave the top uncovered as some light is necessary during winter months.
Rabbits, mice, moles and deer are forced to seek alternate food sources during extended periods of snow coverage. They often turn to flowering crabapple, mountain ash, hawthorn, euonymus and viburnum, among others. Girdling of stems by rodents will kill the plant if complete, and if partial, will create wounds for borers and other disease organisms to enter.
Gardeners should protect stems and trunks of these plants in late autumn with plastic collars cut in a spiral fashion so they many be slipped around tree trunks. Rodent repellents sprayed or painted on trunks, stumps and lower limbs may also be effective.
Gardeners invest significant resources in their home landscapes and will reap the benefits of a little winter care. More information on this timely topic is available at ohioline.osu.edu/hyg-fact/1000/pdf/1648.pdf.
Michele Pearson is an OSU Extension Master Gardener volunteer.