Having a good lawn in a tree-shaded landscape is a challenge since all of the warm-season turfgrasses were developed to grow best in full sun, according to LSU AgCenter horticulturist Dr. Tom Koske.
Homeowners who want the cooling effects and landscaping benefits of shade trees often face a conflict with wanting the grass to receive full sun – meaning six hours or more of direct sun striking the plants.
A moderate or small tree today may have a different canopy in 10 years as the landscape matures. This presents an ongoing challenge to keep a lawn growing under the trees.
"We may need to rethink our wants versus our needs," Koske says.
Sites near trees where grass receives less than four hours of direct sunlight should be considered areas of high-shade stress.
Compounding the issue of reduced growth in shade is that of tree root competition for soil moisture. These problems are more severe with hardwood shade trees compared to pines.
Environmental characteristics of shaded landscapes generally include: filtering and lowering of light quality, lower light intensity, greater relative humidity and stagnant air and greater durations of wet foliage and soil drought.
Koske says the solution is not a matter of feeding the grass more to compensate for a thinning of the sod.
"In fact, extra fertilizer will do more harm than good in creating softer, overfed grass," he notes. The solutions deal with the greatest limiting factors – light and moisture.
High-shade stress areas are often best planted with ground covers, mulched or naturalized. Koske offers several possible solutions to keep grass in areas of moderate shade stress.
– If you can, remove trees that will not seriously detract from the landscape but still allow some shade. If removal is not an option, de-limb lower trunks and thin the canopy to allow more light to pass though to the area under the trees.
– Increase the mowing height to the highest recommended height. For St. Augustine, that's a cut of at least 3 inches, and for centipedegrass, it is 2 inches. St. Augustine has a greater tolerance for shade than centipedegrass.
– Apply moderate amounts of proper fertility to the sod as required by the soil and the turf cultivar.
– Reduce traffic and stress in the shaded areas.
– Remove leaf litter regularly to avoid extra smothering.
Koske adds that more information is available this topic in the LSU AgCenter publication 2909, "Managing Lawns in the Shade."
On the Internet: LSU AgCenter: www.lsuagcenter.com/
Source: Tom Koske (225) 578-2222, or firstname.lastname@example.org