Oak trees (Quercus) are full-sun trees with many different species, thriving throughout U.S. Department of Agriculture plant hardiness zones, with an oak species to fit almost every climate. As large shade trees, oaks grow as much as 80 feet tall with an equal spread. A common problem among large shade trees, grass may have a hard time growing beneath the oak tree’s canopy. Fortunately, there are several remedies for this problem.
1. Minimizing Competition
Your grass is not growing at the base of your oak tree because the tree's canopy blocks sunlight from reaching the turf below. Lack of sunlight coupled with competition from the tree’s root system for water and nutrients results in poor grass growth, browning and bare spots. When planting oak trees in your yard, make sure each tree has enough room to accommodate its height and spread. Allow 40 to 100 feet between each tree to ensure that your entire turf is not shaded. For a tree-shaded property, choose a variety of turf grass that is tolerant of shade or filtered sunlight, such as rough-stalked bluegrass (Poa trivialis), hardy in USDA zones 4 through 7.
2. Clearing Debris and Leaf Litter
Good cultural practices are essential to improve grass growth beneath your oak tree. Make sure the area is well-draining and remove any debris, trash or leaf litter from the base of your tree. They add to the problem of blocked sun light. Debris also harbors water and moisture, which contribute to pests and diseases that harm and prevent grass growth.
3. Increasing Sun Exposure
Opening up the canopy to increase sun exposure at the base of your oak helps to stimulate grass growth. This is done through careful and selective pruning of the inner lower branches of your oak tree. However, as your oak tree continues to grow, repeat pruning is necessary to maintain the desired sun exposure. Pruning your tree is an on-going job, which may be costly if you require a professional to perform the work.
4. Spreading Mulch
You can cover the unsightly problem of poor grass growth under your oak tree by adding 4 to 6 inches of mulch around its base. While new mulch is needed each season, this is an easy fix that also improves the vigor of your tree by adding organic matter to the soil and prevents weeds from growing. Do not place mulch directly against the tree's trunk, as this interferes with aeration and promotes pests and diseases.
5. Planting Shade Lovers
Planting shade-loving groundcovers or annuals around the base of your tree is an alternative to grass that won't grow there. Be careful to avoid harming your oak’s root system when planting directly in the ground. When adding soil on top of the root system for planting, do not add more than 2 inches, to ensure that water and nutrients are still able to flow to your tree. Shade-loving ground covers include ferns like sword fern (Nephrolepis exaltata cordifolia). Sword fern is a fast-growing fern which thrives in USDA plant hardiness zones 8 through 11. Shade-loving annual flowers include wax begonias (Begonia x semperflorens) and impatiens (Impatiens wallerana).