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Trees provide many environmental and psychological benefits. However, trees and turfgrass are not very compatible. Large trees cast considerable shade. Trees also compete with the turfgrass for water and nutrients. As a result, most turfgrasses have a difficult time growing in the vicinity of large shade trees.
Grass Species Selection
One key to successfully growing grass in shady areas is to select the proper turfgrass species for the site. Kentucky bluegrass is the most widely grown turfgrass in Iowa. However, most Kentucky bluegrass varieties do not perform well in shady areas. The fine-leaf fescues (creeping red fescue, hard fescue, chewings fescue, etc.) are the most shade tolerant of the cool-season turfgrasses. When attempting to establish grass in a shady area, select a grass seed mix that contains a high percentage (at least 50 percent) of the fine-leaf fescues. Late summer (mid-August to early September) and April are the best times to establish grass in shady areas.
Proper management practices are also keys to growing grass in shady areas. These management practices differ slightly from those that would be used in full sun.
Do not mow shady areas less than 3 inches in height. Because of the lower photosynthetic rates in shady areas, the turfgrass plants need a large leaf surface to manufacture adequate amounts of food. The recommended mowing height for grass growing in shady areas is 3 to 3 1/2 inches. (A 3 to 3 1/2 inch mowing height is also fine for sunny areas.)
When mowing turf, never remove more than 1/3 of the total leaf surface at any one time. If the mower is set at 3 inches, cut the grass when it reaches a height of 4 1/2 inches.
If possible, alternate the mowing direction from one mowing to the next. Mowing the lawn in the same direction or pattern may damage certain areas. The damage is caused by the mower wheels repeatedly going over the same areas, resulting in soil compaction and physical wear.
The fine-leaf fescues possess good drought tolerance and only need to be watered during prolonged dry periods. When watering, irrigate deeply but infrequently. A single application of 1 inch of water per week is usually best. Early morning is the best time to water turfgrass. Watering in the late afternoon or evening may increase the potential for disease problems.
Turfgrass growing in shady areas requires less nitrogen than turf growing in full sun. Apply no more than 2 pounds of nitrogen per 1,000 square feet per year. September and late October/early November are the best times to fertilize shady lawn areas. To apply the maximum amount of fertilizer, apply 1 pound of nitrogen per 1,000 square feet in September and an equal amount in late October/early November. A single application of 1 pound of nitrogen per 1,000 square feet in late October/early November would be adequate for a low maintenance lawn.
Shady lawn areas often become thin over time because of the difficult growing conditions. Periodically, it becomes necessary to overseed sparse turf areas. The best times to overseed shady areas are late summer (mid-August to early September) and April. Small areas can be overseeded, by carefully raking the site, sowing the grass seed, and then raking the area a second time. A core aerifier may be necessary when overseeding large areas. After the seed has been sown, keep the seedbed moist with frequent, light applications of water to encourage germination.
Growing conditions for the turfgrass can be improved by removing low-hanging tree branches. Pruning off the lower limbs will increase the amount the light the grass receives. It will also increase air circulation, reducing the potential for disease problems.
Fall Leaf Debris
Turfgrass plants utilize light, water, and nutrients to manufacture food. In fall, lawn areas beneath large trees are often completely covered with leaves. The leaf debris prevents the turfgrass plants from manufacturing and storing food prior to winter. To promote turfgrass vigor, rake off the leaves or cut them into small pieces with a mower. After mowing, it's imperative that the shredded leaves do not completely cover the turfgrass.
Despite your best efforts, it may not be possible to successfully grow grass in some areas. For example, growing conditions under hard maples are extremely difficult. Hard maples have very dense canopies. As a result, areas beneath hard maples receive very little light. Hard maples also have extensive, shallow roots that are very efficient at absorbing water and nutrients.
If your efforts to grow turfgrass are unsuccessful, there are alternatives. Areas around and beneath trees can be mulched with wood chips or shredded bark. Planting a shade tolerant groundcover in the area is another possibility. Shade tolerant groundcovers include bugleweed (Ajuga reptans), barrenwort (Epimedium spp.), sweet woodruff (Galium odoratum), hosta (Hosta spp.), and spotted deadnettle (Lamium maculatum). Additional groundcover possibilities can be found in PM-1332 Groundcovers.
IC-497 (9) -- May 2, 2007