Answer: Black walnut trees have a substance within the tissues (called juglone) that effectively inhibits growth of other plants. This defense mechanism keeps other plants from competing for moisture and nutrients. If your tree is a black walnut, this may be contributing to the cause, but more likely the grass won't grow beneath the tree because tree roots of any kind will take up the available moisture, keeping the soil dry. The canopy of the tree can also divert rainwater and cast too much shade for turfgrass to grow well. Tall fescues are the most tolerant of dry shady spots so you might try growing fescue grasses beneath the tree. Or, you might opt to plant a groundcover plant there instead. If you decide to try to grow turf, start by raking the area, digging in some compost and then overseeding. Best wishes with your landscape.
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