Chapter 28 Winterization of the landscape.
Upon completion of this chapter, you should be able to
* list those elements of the landscape that require winter protection
* describe eight possible types of winter injury
* explain nine ways to protect against winter injury
Winter injury is any damage done to elements of the landscape during the cold weather season of the year. The injury may be due to natural causes or to human error. It may be predictable or totally unexpected. At times winter injury can be avoided, while at other times it can only be accepted and dealt with.
Winter injury attacks most components of the outdoor room. Plants, paving, steps, furnishings, and plumbing are all susceptible to damage from one or more causes.
Types of Winter Injury
While the types of winter damage are almost unlimited, there are several that commonly occur. The landscaper should be especially aware of these. Injuries are caused by one of two agents: nature or human beings. There are many different examples within these two general categories.
The severity of winter weather can cause extensive damage to plant materials in the landscape.
Windburn results when evergreens are exposed to strong prevailing winds throughout the winter months. The wind dries out the leaf tissue, and the dehydrated material dies. Windburn causes a brown to black discoloration of the leaves on the windward side of the plant. Very often, leaves further into the plant or on the side opposite the wind show no damage. Broad-leaved evergreens are the most susceptible to windburn because they have the greatest leaf surface area exposed to drying winds. To protect themselves, many broad-leaved evergreens roll their leaves in the winter to reduce the amount of exposed surface area, Figure28-1.
[FIGURE 28-1 OMITTED]
Needled evergreens can also burn. If burn has occurred, brown-tipped branches are apparent in the spring when new growth is beginning. As with broad-leaved forms, windburn on conifers is likely to be confined to the outermost branches on the most exposed side of the plant.
Temperature extremes can also cause injury to plants. Plants that are at the limit of their hardiness (termed marginally hardy) may be killed by an extended period of severely cold weather. Others may be stunted when all of the previous season's young growth freezes.
After some cold winters, certain plants may show no sign of injury except that their spring flower displays are absent. This results if the plant produces its flowers and leaves in separate buds. The weather may not be cold enough to affect the leaf buds, but freezes the more tender flower buds. This is especially common with forsythia and certain spireas in the northern states.
Unusually warm weather during late winter can also cause plant damage. Fruit trees may be encouraged to bloom prematurely, only to have the flowers killed by a late frost. As a result, the harvest of fruit can be greatly reduced or even eliminated. Spring flowering bulbs can also be disfigured if forced into bloom by warm weather that is followed by freezing winds and snow.
Sunscald is a special type of temperature-related injury. It occurs when extended periods of warm winter sunshine thaw the above-ground portion of a plant. The period of warmth is too brief to thaw the root system, however, so it remains frozen in the ground, unable to take up water. Above-ground, the thawed plant parts require water, which the roots are unable to provide. Consequently, the tissue dries out and a scald condition results.
Sunscald is especially troublesome on evergreens planted on the south side of a building. It also occurs on newly transplanted young trees in a similar location. The young, thin bark scalds easily and the natural moisture content of the tissue is low because of the reduced root system.
Heaving affects turfgrass, hardy bulbs, and other perennials when the ground freezes and thaws repeatedly because of winter temperature fluctuations. The heaving exposes the plants' roots to the drying winter wind, which can kill the plants.
Ice and snow damage can occur repeatedly during the winter. The sheer weight of snow and/or ice on plant limbs and twigs can cause breakage and result in permanent destruction of the plant's natural shape, Figures 28-2 and 28-3. Evergreens are most easily damaged because they hold heavy snow more readily than deciduous plants. Snow or ice falling off a pitched roof can split foundation plants in seconds.
Plants that freeze before the snow settles on them are even more likely to be injured. Freezing reduces plant flexibility and causes weighted twigs to snap rather than bend under added weight.
Unfortunately, the older and larger a plant is, the greater is the damage resulting from heavy snowfalls and ice storms. There are numerous recorded accounts of the street trees of entire cities being destroyed by a severe winter storm.
Animal damage to plants results from small animals feeding on the tender twigs and bark of plants, especially shrubs and young trees. Bulbs are also susceptible. Entire floral displays can be destroyed by the winter feeding of small rodents. Shrubs can be distorted and stunted by removal of all young growth. In cases where the plant becomes girdled (with the bark around the main stem completely removed), the plant is unable to take up nutrients and eventually dies.
Certain types of injury are created by people during wintertime landscape maintenance. Some types of injury are due to carelessness on the part of groundskeepers. Other types are the predictable result of poor landscape design. A large number are injuries created because the landscape elements are hidden beneath piles of snow.
Salt injury harms trees, shrubs, bulbs, lawns, and paving. Often the damage does not appear until long after the winter season passes. Thus, the cause of the injury may go undiagnosed.
The salt used to rid walks, streets, and steps of slippery ice becomes dissolved in the water it creates. The saline solution flows off walks and into nearby lawns or planting beds. Paving sometimes crumbles under heavy salting. Poured concrete is especially sensitive to this treatment, Figure 28-4.
[FIGURE 28-2 OMITTED]
[FIGURE 28-3 OMITTED]
[FIGURE 28-4 OMITTED]
Salt is toxic to nearly all plant life. The resultant injury to lawns appears as strips of sterile, barren ground paralleling walks, Figure 28-5. Injury can also be seen on the lower branches of evergreens.
Snowplow damage can occur to plant and construction materials for several reasons. A careless plow operator may push snow onto a planting or a bench. This often results when those unfamiliar with the landscape are hired to do the snowplowing. Other injuries from plowing are the result of design errors. Plants, outdoor furniture, and light fixtures should not be placed near walks, parking areas, or streets where they will interfere with winter snow removal.
[FIGURE 28-5 OMITTED]
Damage to lawns can result when the plow misses the walk and actually plows the grass, scraping and gouging the lawn, Figure 28-6. The grass may not survive if this occurs repeatedly.
[FIGURE 28-6 OMITTED]
Rutting of lawns is the result of heavy vehicles driving and parking on softened ground. When the surface layer of the soil thaws but the subsoil remains frozen, surface water is unable to soak in. Users of the landscape accustomed to finding the ground firm may be unaware of damage caused by vehicles temporarily parked on soft lawns. The soil becomes badly compacted, resulting in unsightly ruts.
Reducing Winter Injury
Some types of winter damage can be eliminated by properly winterizing the landscape in the preceding autumn. Other types can be reduced by better initial designing of the grounds. Still other winter injuries can only be minimized, never totally eliminated.
Windburn can be eliminated in the design stage of the landscape if the planner selects deciduous plant materials rather than evergreen materials. This problem can be avoided in the garden by the use of deciduous shrubs on especially windy corners. If evergreens are important to the design or already exist in the garden, windburn can be reduced by erecting burlap shields around shrubs, Figure 28-7. The use of an antitranspirant may also reduce water loss from plants and thereby reduce the effects of windburn. The antitranspirant must be applied in the autumn and again in late winter. While antitranspirants are fairly expensive, they are more practical for the protection of large evergreens than burlap shields.
Temperature extremes can be only partially guarded against. Where wind chill (lowering of temperature because of the force of wind) is a factor, plants should be located in a protected area. Wrapping the plant in burlap also helps. This has proven to be an effective technique for protecting tender flower buds on otherwise hardy plants.
Certain plants, such as roses, can be cut back in the fall and their crowns mulched heavily to assure insulation against the effects of winter. Likewise, any plant that can be damaged by freezing and thawing of the soil should be heavily mulched after the ground has frozen to insulate against premature thawing.
If the landscaper is trying to prolong the lives of annual flowers in the autumn and a frost is forecast, the foliage can be sprinkled with water prior to nightfall. This helps to avoid damage caused by a light frost. The water gives off enough warmth to keep the plant tissue from freezing.
[FIGURE 28-7 OMITTED]
Sunscald of young transplants lessens as the plants grow older and form thicker bark. It can be avoided on trees during the first winter of growth by wrapping the trunks of the trees with paper or burlap stripping. For other types of sunscald, such as that affecting broad-leaved evergreens, the same remedies practiced for windburn and temperature extremes are effective. Wrapping the plants in burlap or the use of antitranspirants gives protection.
Some sunscald can be avoided by the designer. Vulnerable species of plants should not be placed on the south side of a building, nor should they be placed against a reflective white wall that will magnify the sun's effect on the above-ground plant parts.
Heaving of the turf is impossible to prevent completely. The best defense against it is encouraging deep rooting through proper maintenance and good landscaping practices during the growing season.
Bulbs, groundcovers, and other perennials can be protected from heaving through application of a mulch after the ground has frozen. The mulch acts to insulate the soil against surface thawing.
Ice and snow damage to foundation plants can be avoided if the designer is careful not to place plants beneath the overhanging roof line of a building. If the groundskeeper must deal with plants already existing in a danger area, the use of hinged, wooden A-frames over the plants can help to protect them, Figure 28-8. As large pieces of frozen snow and ice tumble off the roof, the frame breaks them apart before they can damage the plants.
To aid plants that have been split or bent because of heavy snow accumulation, the groundskeeper must work quickly and cautiously. A broom can be used to shake the snow off the weighted branches. However, snow removal must be done gently and immediately after the snow stops. If the branches are frozen or the snow has become hard and icy, removal efforts will cause more damage than benefit.
If breakage of plants occurs during the winter, the groundskeeper should prune the damaged parts as soon as possible. This prevents further damage to the plants during the rest of the winter.
Certain plants, such as upright arborvitae and upright yews, become more susceptible to heavy snow and ice injury as they mature. Often the damage cannot be repaired. Large and valuable plants in a landscape can be winterized in the autumn by tying them loosely with strips of burlap or twine. (Do not use wire.) When prepared in this manner, the branches cannot be forced apart by the heavy snows of winter, and splitting is avoided
[FIGURE 28-8 OMITTED]
Animal damage can be prevented by either eliminating the animals or protecting the plants from their feeding. While rats, mice, moles, and voles are generally regarded as offensive, plantings are damaged as much or more by deer, rabbits, chipmunks, and other gentler kinds of animals. Certain rodenticides (substances that poison rodents) may be employed against some of the undesirable animals that threaten the landscape. In situations where the animals are welcome but their winter feeding damage is not, a protective enclosure of fine mesh wire fencing around the plants helps to discourage animals from feeding there, Figure 28-9.
Salt injury to plants and paving need not be as bad as was illustrated earlier if caution is exercised by the groundskeeper. Salt mixed with coarse sand does a better job than either material used separately. The sand provides traction on icy walks, and a small amount of salt can melt a large amount of ice. Excessive salt has no value; it only kills plants and destroys paving. In very cold temperatures, salt does not melt ice; therefore, in these cases it serves no purpose. Salt can turn compacted snow, which is comparatively safe for traffic, into inches of slush, which is messy and even more slippery. The problem of salt injury can be solved by reducing the amount of salt spread on walks and streets during the winter season. The addition of sand distributes the salt more evenly and provides grit for better traction.
[FIGURE 28-9 OMITTED]
Snowplow damage is to be expected if a designer places plants too close to walks and roadways. Therefore, one obvious solution to the problem begins with the designer. When planning landscapes for areas in which winter is normally accompanied by a great deal of snow, the designer should avoid placing shrubs or other items near intersections or other places where snow is likely to be pushed.
Another type of plow damage is the result of the plow driver's inability to see objects beneath the snow. If possible, all objects such as outdoor furniture and lights should be removed from plow areas prior to the winter season. If it is not possible to move them, low objects should be marked with tall, colored poles that can be seen above the snow.
Whenever possible, snow blowers should be used instead of plows. These machines are much less likely to cause damage.
Rutting of lawns usually results from the practice of permitting individuals to park cars on lawns. The best solution to the problem is to avoid doing so. Otherwise, sawhorses or other barriers offer a temporary solution.
A. Indicate whether the following types of winter injury are caused by natural conditions (N) or human error (H).
1. crumbled paving resulting from too much salt
2. dry, dead twigs on the windward side of a pine tree
3. dried, blistered bark on the trunk of a recently transplanted tree
4. deep ruts in the lawn in front of a house
5. dead branches in a shrub following an unusually cold winter
6. failure of a shrub to flower in the spring
7. perennials lying on the surface of the soil in the early spring with roots exposed to the drying air
8. dead grass next to a walk heavily salted during the winter
9. an upright evergreen split in the center by snow sliding off a roof
10. a young tree girdled at the base
B. Of the types of winter damage in the following list, which ones could be reduced or prevented by proper winterization of the landscape during the late autumn?
1. crumbled paving
2. sunscald on new transplants
3. breakage of outdoor furniture by snow plows
4. rutting of the lawn by automobiles
5. foundation plants broken by falling snow
6. sunscald on broad-leaved evergreens
7. tree limbs broken off by an ice storm
8. bulbs heaved to the surface of the soil
9. windburn on evergreens
10. flooded basement caused by melting snow
1. Look for signs of winter injury in nearby landscapes. Find windy corners where evergreens are planted and check for windburned tips. Visit a shopping center, campus, or park where salt is used on walks and parking lots. Look at the paving and nearby plantings for signs of damage. Note the placement of plants in relation to walk intersections and other places where snow may be piled.
2. Conduct ice melting tests. Freeze four pie plates of water. Apply four different mixtures of salt and/or sand to the surfaces and see which melts first. In the first pan, use all salt; in the second, half salt and half sand; in the third, one-quarter salt and three-quarters sand; and in the fourth, all sand. What conclusions can be drawn from the trials?
NOTE: Returning the treated pans of ice to the freezer (approximately 20 degrees F) will assure that no natural melting occurs. Check the pans every 15 minutes for observations.
3. Demonstrate the damaging effects of salt upon plant life. Grow some experimental plants in advance. Root each plant in a separate container. Apply only water to some of the plants for a week. To others, apply varying dilutions of a salt water solution. To a third group, apply water to the soil, but mist the foliage with salt water several times each day. Record observations of each treatment daily.
4. Demonstrate the reduction of water loss from plant tissue caused by antitranspirants. Purchase a small bottle of antitranspirant from a garden center, or write to a manufacturer and request a complimentary sample. Dilute with water as specified on the label. Using a small pump sprayer, apply the antitranspirant to one of two comparable samples of cut evergreens in vases of water. Be certain to apply it evenly over all needle surfaces. The untreated sample should dry out sooner than the treated one, indicating greater water loss.
5. Repeat the demonstration in #4 using a sun lamp or a fan to simulate the drying effects of sun and wind and the protection offered by antitranspirants.
Jack E. Ingels
State University of New York
College of Agriculture and Technology
Cobleskill, New York
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|Title Annotation:||SECTION 3 Landscape Maintenance|
|Publication:||Landscaping Principles and Practices, 6th ed.|
|Date:||Jan 1, 2004|
|Previous Article:||Chapter 27 Care of the lawn.|
|Next Article:||Chapter 29 Pricing landscape maintenance.|