I read recently about a new gardening craze that is called "Intermingling Plants." The jist of it seems to be that a gardener selects creeping, mat-forming plants and grades them on how vigorously they spread and then plants them with other low growing plants that exhibit the same grade of vigor so that the different types do not overwhelm each other in the same flower bed. Then the gardener selects some taller clumping plants that are capable of growing up through the creeping spreaders in the flower bed.
I thought this sounded pretty cool at first, but the more I thought about it the more I realized that this type of garden is actually as old as gardening itself. I believe this is what happens naturally in most mature gardens. The plants grow together and form colonies, and some gardens turn out pretty well and others not so well depending on which plants win the growing game.
One important variable in this growing game is whether or not there is a clever gardener involved in this process who can help or hinder in the way they edit a bed. Another crucial variable is the degree of skill with which the plant repertoire was chosen initially with respect to the site and its compatibility in terms of the plants' requirements. If sun lovers are planted with shade lovers, for example, in a sunny bed I think we can all guess which plants will win and take over.