It can be difficult to grow grass under a tree because the shade from the branches keeps the sun from reaching the ground. According to University of Connecticut Cooperative Extension, most turf grasses require either four to five hours of full sunlight or 12 hours of partial sunlight per day. It is possible to remedy this and other issues by taking some precautions. Growing grass under a tree takes some work and resourcefulness, but it is possible.
Trim back some of the tree's branches before planting the grass seed. Starting about 10 inches above the ground, clip off branches one at a time with pruning shears until partial sunlight is filtering through to the plot. This will give the grass at least some of the sun it needs to grow.
Select a grass seed that can thrive in shade. Specific types generally vary by region, so if you're not sure what to use ask a specialist at your local gardening center. Some varieties that have a high shade tolerance include rough bluegrass, creeping red fescue, chewings fescue and hard fescue.
Work the ground over with a hand tiller, removing large rocks, loose roots and weeds, then scatter the grass seed on top of the aerated soil. A fertilizer isn't usually necessary, but if you want to use it choose one that contains a low level of nitrogen. High-nitrogen fertilizers can contribute to increased disease and fragility of grass.
Water the shaded grass less frequently than the unshaded grass in the rest of the lawn. The shaded grass will take longer to dry out and should only be watered when the dirt feels dry to the touch.
Limit foot traffic on the growing shaded grass, as tromping on the already delicate area can kill the grass.
Increase the mowing height in that area by about an inch. The taller grass will be able to absorb more light and will also develop deeper roots, which can draw much-needed water and nutrients from the soil.
Rake the shaded grass frequently during the autumn. Thick layers of leaves will further block the sunlight from the already vulnerable grass and can kill it.