You must admit, performing Ode to Joy
with only a blade of grass
is pretty impressive. You can master grass whistling with practice.
The first step to grass whistling is selecting the blade of grass appropriate for the selection of music you are going to play. A simple rule: short blades of grass have higher pitch than long blades of grass.
Place the blade of grass between your left thumb and right thumb. Use your index finger and thumb to hold the blade of grass while you position your other thumb. The edge of the blade should face you, and your hands should look like they are praying.
Place your mouth below the knuckles of your thumbs (there should be a sligh opening where you can blow). Blow steadily until a sound is created from the blade of grass.
You can control pitch by adjusting the tension of the grass. If you release tension, you will get a low pitch, if you increase pitch, you can produce a higher pitch.