Scenic Express sells Heki Wildgrass for modeling perfect looking clumps of tall grass. It's sold in several colors and textures.
In the package there's a large sheet of standing grass on a plastic backing. This is the same type of grass you'd get from the Heki Flock Star static grass applicator only the Wildgrass is ready to use.
Just peel a clump of grass from the backing, put a drop of white glue on the back and push it into the scenery. After the glue dries you have a patch of grass that looks like it just grew there.