Editor's note: Amy L. Dabbs works at the Clemson University Cooperative Extension. She will be a regular columnist, running alternately with Tony Bertauski's gardening column.
Q How can I grow grass under my live oak trees?
A: This is a question the Master Gardeners and I hear often from clients in the tri-county Clemson Extension offices. Home gardeners often are tired of spending money and time on what seems like a losing battle. Perhaps it's time to wave the white flag and seek some neutral ground.
It is possible to grow turf and live oaks in the same landscape, but it will require calling a truce. It also requires an understanding of the
science behind the trees and the turf.
Live oaks (Quercus virginiana) need space, and they don't take kindly to competition for water and nutrients. They also have a kind of plant “super power” called allelopathy, which means their roots and leaves produce a chemical byproduct that inhibits germination of other plants in their immediate vicinity. This natural defensive chemical barrier can cause wilting, yellowing, thinning and even death of nearby plants.
The other issue may be as simple as the amount of sunlight the turf actually receives. St. Augustine or Charleston grass often is touted for its tolerance to shade, but this is a bit of a misconception as it still requires four to six hours of direct sunlight for quality growth. More often than not, lawns are in partial sun under the shadow of maturing oaks, which may lead to weak, thin grass.
Under the canopy
The most peaceful approach is to follow the advice of urban foresters who recommend mulching under live oak canopies to protect roots from soil compaction and soil erosion. Mulching also improves soil and enhances the beauty of these majestic trees in the landscape.
Mulched areas should extend slightly beyond the tree's drip line or the imaginary line on the ground around a tree where the branch tips end and rainwater drips off. Ideally, the leaves of the live oaks should be left to decompose under the canopy to recycle nutrients. If you already have raked and removed the fallen leaves, mimic nature by applying a thin, 1- to 2-inch layer of compost over the root zone. Top with no more than 4 inches of shredded bark or pine straw mulch to retain moisture without smothering roots and depriving them of oxygen.
If your yard is dominated by an old-growth live oak, congratulations on inheriting one of the most sustainable landscapes a gardener could dream of! However, your dreams of a lush turf grass lawn may not be realistic. The good news is that live oaks are ecological powerhouses supporting hundreds of organisms such as Spanish moss, resurrection fern and a host of beneficial native insects, animals and birds.
Protecting your tree
Live oaks need very little water, fertilizers or chemical pest controls. They stabilize soil from erosion and withstand hurricane-force winds better than any other landscape tree. Their presence in a home landscape may increase home values and often contribute to lower energy bills by providing cooling shade and reducing water needs.
The only demands live oaks insist on are space, proper pruning done early in their lives, supplemental watering during drought, healthy soil and protection from injury. Live oaks do not fare well when the soil around their roots is compacted. Activities to avoid include placing large volumes of soil on top of their roots, construction, parking or driving cars or other machinery such as lawn mowers over their roots. When planting near live oak roots, choose plants in small 2- to 4-inch containers to minimize root disturbance. As long as gardeners take their cues from nature, it is possible to garden under live oaks
What will grow
To create a beautiful, sustainable woodland garden inspired by nature, begin by researching plants and observe your site for quality of sunlight (full, part or shade). Consider the amount of time you want to spend on maintenance. Choose plants that are known to do well in competition with tree roots and are tolerant of dry, shady conditions. Most importantly, guard against plants known to become invasive. That means looking beyond the traditional ivy (Hedera species) and periwinkle (Vinca minor) that are both known to escape “captivity” and move into natural areas. Vines should not be allowed to consume trees since they can choke out sunlight and weigh down branches.
Consider native plants such as beautyberry (Callicarpa americana), dwarf palmetto (Sabal minor), upland river oats (Chasmanthium latifolium), Carolina jessamine (Gelsemium sempervirens), sweetgrass (Muhlenbergia filipes), purple mistflower (Eupatorium coelestinum), green and gold (Chrysogonum virginianum), coralbean (Erythrina herbacea) or little brown jugs (Hexastylis arifolia).
Combine these natives with other ornamentals such as autumn fern (Dryopteris erythrosora), holly fern (Cyrtomium falcatum), Solomon's seal (Polygonatum species), cast iron plant (Aspidistra eliator), barrenwort (Epimedium species) and beach wormwood (Artemisia stellerana).
For more home horticulture tips and information, go to the Clemson University Home & Garden Information Center at www.clemson.edu/extension/hgic. To contact a local Master Gardener or for information on how to become a Clemson Extension Master Gardener, go to www.clemson.edu/extension/mg/counties/tri_county.
Amy L. Dabbs is the urban horticulture extension agent and tri-county Master Gardener coordinator for the Clemson University Cooperative Extension. Send questions to firstname.lastname@example.org.