Gardeners are keenly aware of seasonal effects of temperature, particularly freezing temperatures, on the growth of landscape crops. Woody plants are able to survive freezing temperatures because of metabolic changes that occur in the plant between summer and winter. Terms such as cold hardy, frost hardy and winter hardy are used to describe woody plants that can survive freezing temperatures without injury during winter dormancy.
Elton M. Smith, Professor Emeritus, The Ohio State University for the Ohio Florists' Association provides these steps or procedures to guard against winter.
Cold weather and particularly frost, cause the water in plant cells to freeze, damaging the cell wall. Frost damaged plants are easy to spot. Their growth becomes limp, blackened and distorted. Evergreen plants often turn brown and the leaves of tender plants take on a translucent appearance. The main source of trouble during the colder months for even the hardiest of plants is prolonged spells of severe cold when soil becomes frozen for extended periods.
Apply a layer of mulch, 2 to 2.5 inches deep, after the soil freezes to keep the soil cold rather than protect the soil from becoming cold. This practice will reduce injury from plant roots heaving (coming out of the soil) because of alternate freezing and thawing. Plants that benefit from this practice include perennials, alpine, rock garden plants, strawberries and other shallow-rooted species. A mulch maintains a more even soil temperature and retains soil moisture.
Apply bark products, composts, peat moss, pine needles, straw, hay, or any one of a number of readily available materials from the local garden center. Pine boughs or remains from Christmas trees can be propped against and over evergreens to help protect against damage by wind and sun.
Multiple leader (branched) plants such as arborvitae, juniper and yew may be damaged by the weight of snow or ice. Prevent plant breakage by fastening heavy twine at the base of the plant and winding it spirally around and upward to the top and back down in a reverse spiral. This technique is needed more as plants become larger and begin to open at the top.
Narrow and broadleaf evergreens lose moisture through leaves in winter. Since the soil moisture may be frozen, plant roots cannot absorb what is lost and the foliage desiccates, turns brown, and may drop. This can be serious with evergreen azalea, holly, boxwood and rhododendron.
Applying an anti-transpirant, also called anti-desiccant, reduces transpiration, and hence, damage to the foliage. At least two applications per season, one in December and another in February, are usually necessary to provide protection all winter. A number of products are available in most garden centers for this use.
A wrap of burlap or canvas can offer protection to plants against desiccation from sun and wind and drift from de-icing salts applied to drives and streets. Wrap the "body" of the evergreens, but do not cover the top of the plant as some light is necessary during the winter.
Some landscape plants, especially during a time when there is an extended period of snow cover, become a food source for rabbits, mice, or moles. When their normal food supply is covered with ice or snow, rodents turn to the bark and young stems of apple, flowering crabapple, mountain ash, hawthorn, euonymus and viburnum, among others. Complete girdling of stems by rodents will kill the plants and partial girdling creates wounds for borers and disease organisms to enter, as well as weakening the plant itself.
Protect stems and trunks of these plants in late autumn with plastic collars cut in a spiral fashion so they can be slipped around tree trunks. Hardware cloth can also be used as a stem wrap along with aluminum foil.
Trunks, stems and lower limbs can be sprayed or painted with rodent repellents. A number of these materials are available in most garden centers. Repeat the application at least once during a warm period in midwinter. Mixing the repellents with an anti-transpirant often results in extended effectiveness of these products.
Elton M. Smith, Professor Emeritus, The Ohio State University for the Ohio Florists' Association who has granted permission for its use and distribution.