What perennials can I use to plant in my window flower boxes?

I just put up 3 large window boxes, I know late in the season. I am planning for next spring and summer. These window boxes are 6 foot and 8 foot in size, they are 10 inches deep so I can plant perennials. I want to be able to keep my cost down each year so I was looking for ideas of plants that I can use year after year. I live in Ohio (zone 5). I want some plants to hang over the edges and ones that won't become too big and over power the whole box. Ideas? Thanks so much!
  2 answers
  • 360 Sod (Donna Dixson) 360 Sod (Donna Dixson) on Aug 11, 2013
    Are they in sun or shade?

    • 117135 117135 on Aug 11, 2013
      @360 Sod (Donna Dixson) one is full sun, the other 2 are morning sun

  • Douglas Hunt Douglas Hunt on Aug 12, 2013
    DeDe, I think the challenge is going to be finding perennials that will not grow too large for a window box and that will bloom for long enough of a season to make you happy. For the full sun one you might consider dianthus or the "clips" series of Campanula carpatica. Some gaillardias are pretty short and bloom for a very long season. Dicentra eximia might work in the morning sun location. Alchemilla mollis would be good there, too.

    • 117135 117135 on Aug 12, 2013
      @Douglas Hunt Wow, thanks so much! I will research each of these and see what I like! I just want to have a few perennials with the annuals.