2 to 2 1/2cups powdered sugar, you can add more if desired, I usually use less than 2cups because I find it too sweet
1-2tbl milk or heavy cream (optional, I don't always add it)
1tsp vanilla extract or other flavoring, almond and lemon is nice, too.
To pipe grass you will need grass piping tip and also green food coloring to color buttercream.
I used a small round piping tip to pipe the lines.