Jack, this grass texture image link below might work; due to the size of it. It is 22 inches high X 19 inches wide. You could use two of these in this image to make it work. One on the left side of the road and the other on the right side. Then just crop them to the right size to fit. It is already high enough at 22 inches. I just need 18 inches high.
I just look at the resolution. It is only 72 res. This might be a problem when it gets printed out. What do you think?