I’m not sure who first coined this design principle for container gardening…I may have read about it in Fine Gardening. A quick Google search resulted in many hits for “thrillers, spillers and fillers”. Here’s the link to the Fine Gardening Article.
The basic concept is simple. You select 3 levels or focal points for your container. First, the thriller…it can be something tall to draw your eye up or it can be especially showy…basically, your leading role or main event. The filler is the middle layer, supporting roles, if you will. It may be something that contrasts with your thriller, perhaps a medium height flower or something will smaller features. Plants with complimenting foliage that enhance your thriller are ideal. Lastly, the spiller adds some extra dimension and texture to your container.
This photo is actually of a container I threw together when I was thinning out some of the beds. The “thriller” is an Evening Primrose, the “fillers” are two varieties of Lamium and the “spiller” is some Moneywort (Creeping Jenny). It is just beginning to “spill” on the left. I think I have a picture of it from later in the season…I’ll have to see if I can find it.