Got patchy tree islands in your sea of green grass? You’re not alone. In fact, the turfgrass species we grow on our lawns have evolved over millions of years to be adapted to open, sunny environments—not shade (3). So while getting grass to grow under your trees may feel like a Herculean task (it sort of is!), we’re here to help.
Let’s start with the obvious: It doesn’t look good. But aesthetics aside, bare soil can allow moss, algae, and weeds to sneak in and compete with your grass, which is detrimental to the long-term health of your lawn. Plus, exposed soil can lead to sediment pollution in our waterways (4). Also not great.
Keep reading to learn the causes—and what you can do about it.
Not enough light. Feelin’ shady? Grass needs a minimum of four hours of sunlight just to survive; to thrive it needs at least six. Unfortunately, no soil additive can overcome a lack of sunlight that grass needs for photosynthesis. Even if your grass has a direct line of sight to the sun, if it’s in competition with tree leaves, the tree is going to win this one! By the time light passes through the canopy to reach the grass, most of its photosynthesizing power will have been depleted by the tree leaves, and the grass will be spent from searching so hard for energy. (3)
Not enough water. In addition to competition for light, your grass will be going head-to-head with thirsty tree roots, and during drier periods there may not be enough water to go around. A telltale sign of this is dry patches along your drip line (if you have one), which indicate that your lawn is experiencing drought-stress due to trees taking up all the water. (3)
Not enough space. Are you attempting to plant your grass too close to the tree? It’s common for trees to have shallow roots around the trunk, which makes it difficult for grass to obtain water and nutrients. If grass does manage to get established in this zone, known as the “root flare,” it can actually stunt the tree’s growth—or even kill it.
If you’re confident that your grass is getting plenty of light and water and isn’t too close to the tree, there are three other possible culprits to consider. The first is allelopathy (1), in which certain plants release inhibitory chemicals that prevent other plants from growing and developing. Black Walnut and Buckthorn are frequent offenders of this territory marking! Another possibility is that your soil is too acidic or too basic. Extremes in pH (less than 4.5 or more than 8.5) can make nutrients either toxic or unavailable to your grass (2). Finally, consider that environmental conditions under your tree may not be conducive to good growth: Cooler temperatures, higher humidity, lack of air movement, incorrect moisture levels, and leaf cover in the fall can all prevent your grass from growing well—or at all (3).
Start by determining your grass type, because this may rule out certain solutions. Not sure what type you have? We made a guide for that!
Diversify your grass. Some cool-season grasses have a degree of tolerance for shade. If your yard has a lot of trees, you may want to consider the following grasses, in order of most shade tolerance to least (3):
Live in the south? You should probably plant zoysia as it’s the most shade-tolerant warm-season grass species. But remember, even the most shade-tolerant warm-season grass is not as resilient as the least shade-tolerant cool-season grass.
Sunday ProTip: Change up your typical lawn routine under the tree canopy! Raise your mowing height to allow for more grass surface to photosynthesize, apply less than half the rate of fertilizer to limit nitrogen levels, and water or irrigate these zones less to limit moisture influx.
If you want to give this method a go, check out our family of Sunday seed blends, and choose based on your yard’s sun exposure, water requirements, and tree coverage. When the time comes, you can grow like a pro with our overseeding cheat sheet.
Prune your trees. Both cool- and warm-season grasses might just need a little more sunlight per day, and in some cases you can achieve this by cutting branches off your trees. This method will minimize the blocking of critical sunlight to the grass below the canopy (3).
Sunday ProTip: Don’t try this at home, folks—at least, not by yourself. Tree pruning is more complex than just cutting off a few branches, and unless you’re skilled at this, it’s best to hire a professional as this method can be labor-intensive, harmful to the tree (if cut improperly), and even dangerous.
Don’t grow grass. Not something you think we’d say, right? Well, if grass just isn’t growing and you don’t want weeds to move in, it’s okay to find alternative solutions. Non-invasive cultivars like English ivy or common periwinkle can prevent weeds, keep soil in place, and help fill in bare patches with thick, green groundcover. Not worried about a green understory? You can always mulch around trees for an aesthetically pleasing—and less labor-intensive!—solution (3).
Sunday ProTip: Since your lawn is already stressed and not growing effectively, it’s more susceptible to weeds, diseases, and pests. Monitor for these things and treat as necessary.
Ready to give it a go? Our lawn advisors are always on hand to answer any questions you may have. But once your neighbors see your patch-free lawn, you may be the one handing out advice!