A frequent question I get each year is: "How do I get grass to grow under the shade of my trees?" Most turf grasses grown in the Lakelands are warm season grasses, such as Centipede, Bermuda, Zoysia or St. Augustine. Even though some, such as St. Augustine, tolerate a limited amount of shade, all turf grasses mentioned above need sunlight, water and nutrients for good growth and performance. Trees compete with turf grasses for all their needs.
Another complication when discussing growing grass in shade is the level of light versus shade, which is often related to individual tree characteristics. Things such as tree species, size, and spread of the tree, density of foliage, and height to the first branches affect the amount of light that reaches turf at ground level.
Pruning branches of large, older trees to allow more sunlight is difficult, often expensive and can create large wounds on the tree. This work is best left to professional tree companies. Where younger, smaller trees are planted within turf areas, a better approach to both trees and turf is possible. This begins with creating a mulch ring around the young tree to reduce grass competition while it grows. The mulch ring will eliminate the need to use mowers or weedeaters near the base of young trees that are easily damaged.
A mulched zone near older trees might be better too, when large roots are exposed near their trunks. This complicates management of grass growth and maintenance under their canopies, but provides more protection to exposed surface roots. Mowers used to cut grass near trees often damage the tops of roots that are at the surface, or just above ground level. This damage can lead to root decay that weaken the tree roots over time. Trees with damaged or diseased roots are more susceptible to windthrow from storms and wind as they age.
Another practice, mowing in a circle around trees to cut scattered grass and weeds, often blows more soil away from surface roots which decreases the chances for grass growing well there. Removing soil exposes roots to move damage from the mower blades at the next mowing. Unless your older trees have been pruned on a regular basis to raise the live crown and increase side light penetration over time, it is often better to create a mulch zone near older trees to protect them from damage too. This ring of organic mulch will protect tree roots and create an acceptable visual view of the tree and turf areas.
Young trees should be pruned on a regular basis to raise their crown gradually to allow access under the tree and provide sunlight for nearby grass as they grow. Always leave 60 percent live crown after pruning to develop healthy and strong trees. Removing lower limbs every couple of years will raise the crown of young trees so that grass can still thrive near trees. Be sure to prune limbs off properly; don’t leave stubs or use flush cuts against the tree stem.
For information on proper tree pruning, check Clemson University’s HGIC website at clemson.edu/extension/hgic/plants/landscape/trees/hgic1001.html.