By Bev Tavener, Piedmont Master Gardener Intern
Question: My lawn area is generally pretty lush, but under my big oak, the grass is not growing well. I have fertilized the area with no improvement. What should I try doing?
The Challenge
Growing and maintaining grass in shady areas of the lawn is difficult at best. Turfgrass requires a minimum of 6 hours of direct sunlight or a full day of filtered sunlight and more shade-tolerant grasses typically require 4 hours of sunlight to thrive.
A dense canopy of mature trees, like oaks or maples, hinders grass growth because of both limited sunlight and photosynthesis. Tree roots outcompete grass, taking up the water and nutrients necessary to maintain healthy grass. The dense leaf structure of large trees prevents much water from falling under the canopy. In addition, feeder roots of large trees spread out far beyond the drip line (outer perimeter) of the foliage. In fact, oak tree feeder roots extend up to two to three times farther than the tree canopy and capture rain falling beyond the perimeter. As the grass thins out, it becomes more susceptible to drought, disease, insect pests, temperature variation and wear and tear. Similar problems can occur when buildings, shrubs or tall plants shade grass. It is no wonder that turfgrass rarely grows in forested areas.
Care and Maintenance of Shade-Tolerant Grass
If maintaining the grass in the shade is a priority and the grass under oaks, other large trees or shady areas is not performing well, there are two options.
- Replace it with a grass appropriate for shade and the site. For Central Virginia, fine-leaf fescues, like hard fescue, chewings or creeping red fescue are recommended as the most shade-tolerant and tall fescue is recommended for moderate shade.
- Try to revive the existing grass by improving growing conditions.
In either case, use the following techniques.
- Mow the shady area grass to a height of no less than 3 – 3 ½ inches and do not remove more than 1/3 of the height of the grass.
- Water only during periods of prolonged dry periods, early in the morning and no more than 1 inch per week.
- Use fertilizer sparingly and apply it in the August – October timeframe. Grass grown in shade needs less fertilizer than grass grown in sun. If the soil has not been tested in the last 3 years, get a soil test and follow the recommendations on pH, nutrients and fertilizer.
- Overseed the shady area periodically if the grass thins out. Early fall is the best time.
- Prune and thin the dense canopy and remove (limb) branches up to a minimum height of 6 feet. No more than a quarter of foliage-bearing branches should be pruned at one time. Hire a certified arborist to ensure that pruning is done correctly and large branches are removed safely. Note that pruning will be needed periodically as tree branches grow back.
- Remove leaf debris in the fall or cut leaves into small pieces with the mower to allow grass to produce and store food for the winter.
Alternatives to Shade Grass
Even with proper care, growing grass under large oaks or other trees is unlikely to be a winning combination. Other alternatives can offer benefits, including beauty, habitat for wildlife, low maintenance or all of these.
- Shade-loving native plants can provide a green backdrop and add color to the landscape. Consider native plants, including shrubs, vines and groundcovers, suitable for the site, especially those that will withstand the drier conditions found under the tree canopy. Because native plants have evolved and adapted to local soils, they can thrive in situations where other plants fail. They provide habitat for wildlife and support healthy ecosystems. They also require less water, fertilizer and pesticides and are usually low maintenance.
- A layer of hardwood mulch spread 2 to 4 inches thick and extended to the edge of the tree canopy can be an easy-care solution. The mulch will reduce moisture loss, suppress the growth of weeds and feed the soil below as it breaks down. A word of caution: Avoid making a “mulch volcano”. Don’t mulch too high around the base of the tree. Be sure the root flare (the portion of the trunk where the main roots are attached) is exposed. Remove any soil that covers the root flare. This will prevent rot and allows more oxygen into this area. Studies have shown that this will demonstratively improve tree color and vigor.
Whether planting new shade grass under trees, substituting native plants for thin grass or mulching the shady area, you will need to remove the existing grass first. An easy way to do this is to cut any existing vegetation to a short and even height or remove weeds and grass by hand. Lay down several layers of newspaper and cover with 2 to 4 inches of mulch. The vegetation underneath should disappear quickly. If mulching or pulling up the grass by hand, be sure not to harm tree roots.
There are a wide range of other lawn alternatives available for gardeners who want to go further than just reviving or replacing grass under trees. Limit the size of your lawn by adding a pollinator garden, rain garden, vegetable garden, or edible, annual or perennial borders along paths and driveways. Convert some of your landscape to a meadow or plant more trees and shrubs.
Benefits of Planting Oaks and Other Keystone Plants
Keystone plants, like oaks, play a major role in supporting both healthy ecosystems, including the food web. For example, native oaks host hundreds of caterpillar species and insects, providing food birds and other wildlife. They are also efficient at reducing stormwater runoff and removing pollutants from the air and water. Adding more keystone trees, shrubs and other plants is a good way to shrink your lawn.
Image (cropped):
“Oak Tree” by MunstiSue is licensed under CC BY-ND 2.0.
References
“A Green Solution to Stormwater Management”, Controne, Vincent, Extension Educator, Urban Forestry, Penn State Extension, 27 Oct 2023.
“Fall Into Your Cool-season Lawn: Selecting the Best Grasses”, Virginia Tech, Virginia Cooperative Extension, 2024.
“Keystone Native Plants”, Plant Virginia Natives.
“Keystone Native Plants 101”, Norling, Meg, The Garden Shed, Vol.9, No.9, Piedmont Master Gardeners, Sept 2023.
“Grass doesn’t always grow under trees”, Bogren, Richard & Gill, Daniel J., Louisiana State University, LSU Ag Center, 4 Apr 2014.
“Growing Grass in Shady Areas”, Jauron, Richard & Steil, Aaron, Iowa State University Extension and Outreach, July 2022.
“Growing Grass in the Shade”, University of Maryland Extension, 24 June 2024.
“Lawn Alternatives”, University of Maryland Extension, 24 June 2024.
“Mulching Landscape Trees”, Jackson, David R., Former Extension Educator, Renewable Natural Resources, Penn State Extension, 12 Apr 2018.
“Native Plants”, Piedmont Master Gardeners.
“The Cool-Season Turfgrasses: Basic Structures, Growth and Development”, Landshoot, Peter, Professor of Turfgrass Science, Penn State Extension, 19 Dec 2022.
