waist-high 
adjective & adverb
Of or at a height to reach the waist: [as adjective]: a ruin surrounded by waist-high grass [as adverb]: weeds grew waist-high...
- Students carry measuring instruments down a ditch, through waist-high grass, and wade into the stream to measure stream flow and water clarity.
- He was put to work digging a quarter-acre section of waist-high grass.
- It has oak trees that are hundreds of years old, towering cottonwoods and sycamores and secluded areas where acres of trunk-to-trunk pecan trees haven't yet grown waist-high.