While discussing installation of new sod with customers, a very common question I hear is this: How close to the trees can we plant grass? The answer is complicated, and technical, so let’s break it down.
This Bermuda lawn is set back from the trees where it can get at least 5 hours of direct sun each day. Areas of heavy shade closer to the trees are filled with hardscaping and planted beds. Photo by Hillary Thompson.
All plants need these things to survive: light, air, water, and nutrients. They also need space to grow and favorable temperatures.
Trees and grass are both seeking water and nutrients from the soil. While the roots of your lawn tend to grow 6-12” deep, tree roots go much deeper and wider so there might be tree roots under your sod fighting for the same resources. This means sod that is growing near trees will require more irrigation and more fertilizer than other parts of your lawn. The need for additional water can be mitigated somewhat by the shade the tree provides, but in a drought the tree will win the battle for available water every time.
While the shade beneath trees helps keep you cool, it is blocking sunlight from reaching the ground where you might want to grow a lawn. Grass, like all plants, needs sunlight to produce food and grow through the process of photosynthesis. Different varieties of grass have different tolerances to shade but they all need a certain amount of direct sunlight every day to thrive. No grass likes heavy shade!
So how do you determine where the sod line should stop as you approach a tree?
This small area of Tall Fescue lawn adds a lush look to the wooded front yard. The section closer to the trees is too shady for Fescue to grow so a thick layer of pinestraw mulch has been added. Photo by Hillary Thompson.
First, let's get familiar with some important terms and abbreviations:
My diagram illustrates some of these measurements and terms. Drawing by Shannon Hathaway.
Let's look at some other terms that are important to understand:
This is a perfect example of "dappled sun". This Zenith Zoysia lawn gets direct sun at other times of day and shady areas close to the trees are mulched. Photo by Iris Ramirez.
Canopy trees are most often (but not always) deciduous trees. Different tree species have different canopy spreads, so knowing the tree species can be very helpful. Let’s use a red maple as our example. The canopy of a mature red maple is about equal to its height. (For comparison, the canopy of a mature red oak is about 3/4 its height.)
Now let’s do some math. If the diameter at breast height (DBH) of a red maple in your yard is 1 foot then we can calculate the following:
If you are planting sod on the south side of this red maple with a 1’ DBH, and the canopy is above your head, you can lay sod up to 9 feet (9 x DBH) from the trunk of the tree. On its east and west sides you can come within 12 feet (12 x DBH). On the north side you should avoid the drip line entirely so at least 13-14 feet. Notice this is not a perfect circle! The ground beneath the south side of your tree will receive more sun and under the north side it will have more shade.
On the simplified landscape plan below we are looking down onto a garden and the tree marked B in lower left is a canopy tree in the corner of the front yard. In the top right corner you will see North has been marked and is pointing toward the back of the yard. Notice how the line that marks the edge of the proposed lawn goes under the drip line on the southern side of the canopy tree and then is much further away from the drip line on the north side.
This simple landscape plan shows where the sod line for a new lawn should be to accommodate two trees in the yard. Drawing by Shannon Hathaway.
Conical trees are most often (but not always) evergreen and are shaped like upside-down ice-cream cones. Let’s use a Green Giant arborvitae as our example. The widest part is not above your head but at your feet because the branches grow almost to the ground and that means you cannot grow grass under its base.
However, you CAN bring your sod line in much closer to a conical tree than to a canopy tree because the tree gets narrower as it goes up and it casts less shade than a tree like an oak. On the south side you can bring the sod within 1-2’ of the reach of the lowest branches. On the east and west sides you can do the same. On the north side, however, you will need to stay 4-5’ away from the reach of the lowest branches. On the landscape plan above, the tree marked A at the corner of the house is a conical tree.
As the tree grows, the sod line will likely shrink back. That is because the shade line will increase, as will competition for water and nutrients from the tree roots.
When I meet with clients and we discuss the reality of the tree canopy, many ask, “So how can I have a lawn with all these trees?” The answer is threefold:
The lower limbs have been trimmed from two tall trees on the right to reduce the amount of shade on this Bermuda lawn. Photo by Hillary Thompson.
Now you know how close to the trees you can plant grass and with careful planning you can have a beautiful lawn. Follow these guidelines for success because the game of grass vs. tree is like a Pop Warner football team vs. the Georgia Bulldogs. We all know who will win!
Got more questions about grass for shady yards? Click that link to see other resources to help you answer all those questions or stop by your local Super-Sod store and talk to one of our experts.