Winter landscape maintenance

Even though it is winter, the landscape has something to offer, said a University of Illinois Extension horticulture educator.

“Interest can come in the form of ornamental grasses, trees, and shrubs with interesting bark patterns or ornamental bark such as river birches and paperback maple (Acer griseum), cornelian cherry (Cornus mas),colored stems such as the red-twig and yellow-twig dogwood, plants with berries such as Japanese barberry (Berberis thunbergii) and fragrant sumac (Rhus aromatica), and winter flowers with unique textures, forms, or habits,” said Anne Gachuhi.

“Evergreen trees and shrubs make the landscape look even greener, and they come in a variety of forms and sizes. But it is important to plan a landscape that has winter interest,” Gachuhi added.

Winter can be an extremely difficult time for plants. Cold winter winds and dropping temperatures, freezing rain, snow, and roadside salt injury makes maintaining the winter landscape quite challenging.

“Salt sprayed to reduce the effects of snow and ice along roadsides does eventually affect trees and plants that are close by,” she said. “The effects of salt sprays are usually bud death and twig dieback on trees and shrubs. High salt accumulations in the soil damage plants, causing abnormal fall color, needle-tip burn, and browning of leaves.

“Roadside salt injury on plants can be prevented by planting trees at least 60 feet from the road, planting less sensitive trees such as Ohio buckeye, ginkgo, and white ash, using coarse salts and less de-icing salts on the sidewalks.”

In the wintertime, temperatures may drop drastically within a relatively short period of time. The ideal situation would be to have gradual temperature drop rather than this type of extreme temperature drop, Gachuhi noted.

“The low temperatures cause winter injury or freezing injury to trees and shrubs, which results in damaged root systems and flower buds, and leaf buds, as well as twigs and branches that die suddenly,” she said. “The rapid temperature changes often cause freeze cracks on the bark and splitting of trees on the southwest side. Trees with thick barks such as maples, lindens, and cherries are very susceptible to this situation.

“Protect trees that are prone to frost cracks by wrapping them with tree wrap.”

Plants that are exposed to long periods of very chilly temperatures (zero to below-zero) and bitterly cold winter winds are more likely to suffer winter burn/desiccation injury or low-temperature injury.

“Desiccation injury occurs when plants dry out since they are unable to take up water from frozen soils, causing the above-ground plant parts to dry out,” she explained. “Where possible, commercial anti-transpirants that help to prevent drying out of plants can be sprayed on susceptible plants in late fall when temperatures are not freezing.

“Unfortunately, the low-temperature injury or desiccation injury is not detected immediately but later in the spring, when it shows up in plants that exhibit lack of flowering, sudden wilting, and collapsing. Growing hardy plants and keeping plants healthy enables them to withstand the ravages of the brutal and rapid winter temperature fluctuations.”

Needle evergreens, such as yews and broadleaf evergreens like holly, rhododendron, and boxwoods are very susceptible to desiccation and winter burn, particularly during windy conditions.

“These evergreens often will lose water in cold weather through their leaves,” she said. “That’s why it is important for landscape plants to be well-watered in the fall before freezing winter temperatures occur.

“Broadleaf evergreens should be planted on the east side of the building, where they are protected from winter winds and the late afternoon sun. On the other hand, when winter comes with a good snow cover, it actually benefits herbaceous plants—perennials, bulbs, groundcovers, etc.—by acting as an insulator to the soil.”

When this occurs, she added, it prevents soil/frost heaving caused by alternate freezing and thawing cycles.

“Soil heaving causes plants with shallow root systems to be pushed out of the soil, exposing them to cold temperatures, drying winds, and results in plants drying out,” she said. “A 2-inch to 4-inch mulch layer of wood chips, shredded leaves, and any other organic mulch will reduce soil heaving.”

From the Jan. 17-23, 2007, issue

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