At Torrance I did a simple demo on creating grasses starting with a very loose wet into wet under painting and when it was dry adding very quickly both positive and negative shapes to create a natural looking grass.
|This was done quickly even the under painting (right side )|
always using "grassy" strokes. I wasn't painting a wall.
It is always good to practice a technique on another piece of paper so you understand what you are doing. Studies are a good thing.