Q.use of river rock in areas where pin oak roots prevent growing grass?
plant suggestions with river rock in areas where pin oak roots prevent growing grass?
Shading as well as root density and competition for water and nutrients may be responsible for the suppression of grass. The same conditions will make it difficult to grow other plants.
Consider mulching the soil surface with wood chips or commercial mulch material instead of using river rock. The mulch will have a more beneficial effect for the soil fertility and the trees.