The Thriller is the show-stopping centerpiece of your container design. It adds height, drama, and movement. Thrillers can be flowers, ornamentals or even grasses, just as long as they are the focal point of your container garden arrangement.
If your container will be visible from all sides, place the Thriller in the center of your container for maximum impact. If your container will only be visible from one or more sides, place the Thriller toward the back of the container.
courtesy of Home Depot