Problems Associated with Shade
Tree leaves can substantially reduce the amount and quality of sunlight reaching the turfgrass. Food reserves of plants growing in very dense shade are typically drained, resulting in weak plants. Shade varies with the season, the characteristics of the trees, and where they are located on the lawn. Maples, oaks, and beeches are examples of trees with dense canopies that intercept most of the light. Some evergreens such as firs and spruces have very dense canopies but affect small areas of turf because of their narrow canopy. Pines, poplars, ashes, and birches produce a more open shade than maples and oaks. Areas with an understory, or with trees close together, cast very dense shade. Leafless deciduous hardwood trees can block out nearly 50 percent of the sunlight in the winter, whereas the same trees in full leaf can block nearly 95 percent of summer sunlight.
Shrubs and shallow-rooted trees such as willows, maples, and beeches compete strongly with turfgrasses for nutrients and water. In clay soil, most of the shade trees' feeder roots grow in the upper eight inches where turfgrass roots grow. Competition extends past the trees' drip zone, since roots can grow a considerable distance beyond this point. Reduced amounts of light, nutrients, and water produce succulent, weak turfgrass plants. They are slow to establish and are susceptible to insects, disease, and environmental stress. They are less able to withstand traffic than plants grown in full sunlight.
Environmental conditions associated with shade favor some diseases. Poor wind movement and reduced sunlight moderate the temperature and increase the relative humidity in shady areas. As a result, foliage remains wet for extended periods. Although dew forms less frequently in shaded than sunny locations, it lasts longer because the trees hinder drying. Wet foliage encourages disease development, and thus it is important to select disease-tolerant turfgrasses.
Strategies for Managing Lawn Grasses in the Shade
Modifying the Environment. Turfgrasses will not grow in very heavy shade or under dense leaf cover. If an area gets less than 50 percent open sunlight or less than four hours of sunlight per day, it is much too shady for turfgrass to grow well. Consider removing selected trees, especially if existing trees are too close together and removing them will not detract from the landscape design. Use ground covers such as English ivy, ajuga, liriope, and pachysandra as well as pine bark and needles, crushed stone, and woodchips as an alternative to turf when shade is excessive. These ground covers are more attractive than a thin, dead lawn. For more information, refer to Extension Service publication AG-75, Ground Covers for North Carolina. A turffree zone at least two to four feet in diameter around a tree can improve the growth rate of small plantings by minimizing competition between tree and turf roots for nutrients and water.
Removing tree limbs up to a height of 6 feet and cutting out unnecessary undergrowth will enhance wind movement and reduce the potential for disease. Selective pruning of the tree's crown will open the canopy and allow more light to reach the turfgrass. Removing dead and diseased limbs can enhance the health and appearance of the tree if pruning is done selectively and with care. Avoid severe pruning.
Tree-root pruning also aids in lawn performance, but care must be taken not to injure desirable trees. Maples, beeches, oaks, and certain evergreens are very sensitive to extensive root pruning. Roots should be cut cleanly, and no more than 40 percent of the functioning roots should be removed at one time. Supplemental irrigation and fertilization help reduce the harmful effects of root pruning.
The depth of shade within the dripline of a tree can result in soil erosion, exposing surface roots. Willows, elms, and maples are notorious for their surface roots. One temporary solution is to cover these surface roots with three to four inches of mixed topsoil and organic matter. Shade-tolerant ground covers can be established in these areas to give a pleasing appearance and minimize mowing problems.
Proper tree selection and placement can help minimize turf loss. Trees with dense canopies, shallow root systems, or both, such as willows, poplars, ashes, and certain maples, should be avoided in favor of more desirable species such as oaks, sycamores, and elms. Contact your county Extension center for a list of the shade trees that perform best in your location.
Grass Selection. Using shade-tolerant cultivars is important when growing turfgrass in partial shade. Mixtures of tall fescue in combination with shade-tolerant cultivars of Kentucky bluegrass (80 percent and 20 percent by weight, respectively) are the best choices in most locations where cool-season grasses can be grown (see Table 1). The addition of a fine fescue, specifically cultivars of hard fescue, is beneficial in areas that will receive little maintenance. A mixture of 80 percent tall fescue, 10 percent Kentucky bluegrass, and 10 percent hard fescue by weight seeded at six pounds per thousand square feet is recommended. Other fine fescues, such as certain cultivars of creeping red and chewings fescues that perform well under low light intensities in other states, are thinned by disease in North Carolina. Perennial ryegrass and Sabre rough bluegrass (Poe trivialis) have also performed poorly in shade trials in North Carolina.
Do not permit leaves to accumulate on the new lawn. As leaves fall, they become layered and create a mat that blocks light, air, and water movement. Remove leaves frequently until the grass is established. Some seedlings may be torn out by the rake; however, more seedlings will be lost if the leaves remain.
In general, warm-season grasses often suffer more winter injury in shaded areas than in open, sunny locations. St. Augustinegrass is the most shade-tolerant of the warm-season grasses, followed closely by zoysiagrass. Both Emerald and Meyer varieties of zoysiagrass are more widely used in North Carolina because they tolerate cold better than St. Augustinegrass. Centipedegrass and bahiagrass perform well under light pine-tree shade but are not as shade tolerant as St. Augustinegrass and zoysiagrass. Bermudagrass is the least shade tolerant of the turfgrasses and should not be considered for use in shady areas. Table 1 and Table 2 list shade-tolerant grasses and grass mixtures. Figure 1 shows the boundaries of the three areas of adaptation in the state.
Cultural Practices. Keep in mind that shade-tolerant grasses prefer sunny locations. Lawns grown in the shade must be managed more carefully because they are often weaker than turf grown in full sun. Cultural practices must be altered to help ensure survival and enhance performance. Mow grasses at the top of their recommended mowing height range to promote deep rooting and to leave as much foliage as possible to manufacture food for the plant (see Table 1).
Lawn grasses grown in the shade should generally be fertilized at the same time as turf grown in the sun, but at a lighter rate (see Table 3). Lawn fertilization is not harmful to trees and shrubs and may actually be beneficial. Fertilizers associated with turf, such as 12-4-8 and 16-4-8, can help to meet the requirements of trees and shrubs, thus preventing a nutrient deficiency. (Nutrient status can be confirmed by submitting a soil sample to the NCDA&CS Soil Testing Laboratory in Raleigh.) If the trees require more nutrients than can be supplied by the turfgrass fertilizer, apply additional fertilizer by soil injection or drill coring to reduce the amount of area affected and minimize the potential for turf injury or loss. Keep track of the total amount of fertilizer applied to a given area so the total recommended amount for any plant is not exceeded. Overfertilization may occur if different people are responsible for the trees, shrubs, and lawn.
Irrigate the lawn deeply and infrequently to encourage deep rooting of trees and lawn grasses, reduce soil compaction, and minimize the time that the foliage is wet. Wet foliage promotes disease development.
Remove accumulating leaves frequently from a young lawn. The tender seedlings cannot stand long periods without adequate air, light, and water. Once the lawn is established, and if the mat is not too thick, the leaves can be mulched with a lawn mower. The mulch will decay and add organic matter to the soil. However, if the cover is too heavy, it is best to remove the leaves.
Weed Control. Mosses (small green plants with leaves arising from all sides of a central axis) are very competitive in cool, moist, shaded locations – for example, on the north side of buildings and in wooded areas. Conditions favoring the growth of mosses are low fertility, poorly drained soil, acidity, frequently wet soil, soil compaction, excessive thatch, or a combination of these factors that lead to thin, weak turf. Physical or chemical removal provides temporary control unless growing conditions are improved. Moss can be controlled with copper or ferrous sulfate sprayed at five ounces per thousand square feet in four gallons of water. Applying concentrated amounts (10 ounces per thousand square feet) of ferrous ammonium sulfate when the moss is damp offers another means of control. Applying 5 to 10 pounds of ground limestone per thousand square feet before reseeding helps to inactivate the copper sulfate, which may be toxic to seedlings. Physical removal of the moss by raking may be needed to allow for recovery.
Because crabgrass and goosegrass seed usually need high light intensity to germinate, preemergence herbicides are not required in heavily shaded areas. Be careful when applying broadleaf weed controls because some herbicides can injure trees and shrubs by root uptake or spray drift. Read and follow all label directions carefully.
Disease Control. Powdery mildew, brown patch, leafspot, and melting out are the major turfgrass diseases associated with shade. Powdery mildew is particularly severe on Kentucky bluegrass; however, most shade-adapted cultivars exhibit good tolerance to this disease. Brown patch is often associated with tall fescue, whereas leaf spot and melting out are associated with fine fescue, St. Augustinegrass, and Kentucky bluegrass. (See Extension publications AG-360, Diseases of Warm-Season Grasses, and AG-361, Diseases of Cool-Season Grasses, for a description of the symptoms of these diseases and suggested management practices for minimizing development and damage.) Planting improved, shade-adaptable lawn grasses and using good cultural practices can help reduce damage from diseases. A blend or mixture of improved, adapted cool-season grasses, rather than a single cultivar, can help reduce the potential of turf loss from disease.
Integrated Pest Management
The Sensible Approach to Lawn Care
Many pest problems can cause your turf to look bad – diseases, weeds, insects and animals. If you are really unlucky, you may have all of them at one time.
So what do you do? Use a pesticide? Or make changes in cultural practices? Both methods, and some others as well, may be needed. The balanced use of all available methods is called integrated pest management (IPM).
The idea is simple. It urges the use of all available prevention and control methods to keep pests from reaching damaging levels. The goal is to produce a good turf and minimize the influence of pesticides on man, the environment, and turf.
IPM methods include:
Use of best adapted grasses.
Proper use of cultural practices such as watering, mowing, and fertilization.
Proper selection and use of pesticides when necessary.
Early detection and prevention, or both, will minimize pest damage, saving time, effort, and money. Should a problem occur, determine the cause or causes, then choose the safest, most effective control or controls available.
When chemical control is necessary, select the proper pesticide, follow label directions, and apply when the pest is most susceptible. Treat only those areas in need. Regard pesticides as only one of many tools available in lawn care.
To learn more about integrated pest management, pest identification, lawn care, and proper use of pesticides, contact your county Extension center.
Publication date: March 1, 1998
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.
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