I plant them in a way that each of it's neighbors have an entirely different look. That way if they start to grow into each others territory I can tell them apart when thinning.
I love to have the colors mixed through out the bed for contrast. For me it adds interest.
Last fall I started adding small type alpine plants for more color throughout the growing season, and bulbs that produce miniature plants that won't over take the semps.
http://garden.org/thread/view_...
