Answer: Inspite of good care, it is difficult for turfgrass to thrive under oak trees. First, the canopy shades the lawn, couple that with soil on the dryish side and competition from the tree's roots for moisture and nutrients, and you can understand how turf will grow thin and sparse beneath large trees. You can temporarily improve the situation by aerating and thining out the canopy but eventually the canopy will regrow and the soil will again become compacted. If you don't mind doing these things on a regular basis, you can add more sod or springs to the area beneath the tree and plan on aerating and thinning the tree branches out every 2-3 years. Or, you can reclaim the area by planting a groundcover that thrives in dry, shady soil such as pachysandra.
Best wishes with your turf!
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