Create a new layer.  Press Ctrl + L and load the Alfalfa nozzle.  Set the Size: to 50%.  Paint in some alfalfa until you have something that looks like this (23).   Name this layer Alfalfa.

My  finished painting looks like this.

There are many different effects you can apply to change mood of this type of painting.  Try adjusting the colors, add some lights, play with the opacity of the layers; most of all, have fun at what you are doing.