Purple salvia would be pretty.

Purple salvia and white hardy geraniums would make a good combination. The the more bluish "annual" (actually, tender perennial, hardy to Zone 7--we plant it as an annual) salvia would look great also. Or any combination of blue and white along with the pink--classic "British" combination. If you wanted another rose out there, the mini "Green Ice" might work fine for your white color. It sprawls a bit. Or Gourmet Popcorn rose might work well there (white).

Or, some of the shorter daylilies--an assortment ranging from light pink to dark (nearly black) wine red--with a dose of the bi-colors in there--would look good, as long as you picked some contrasting colors. You don't want everything bubblegum pink, after all. Daylilies can often take care of themselves--with a minimum of attention to their water needs, that is.

The more I think of it, I'm seeing white and a very dark wine red at the feet of your pink Knockouts. Of course, that may just be my own taste. : )

Good luck.

Kate

My lavender munstead in the front of pink knockouts is gorgeous.

Thank you all for the suggestions. Kate, what do you think about one of the Austin reds, such as Munstead Wood, for a wine red compliment?

If Munstead Wood stays dark most of the time, it would be great, but I have never seen it in real life, so I don't know how good a rose it is--although the description looks very promising. I did a quick google search--several bloggers mentioned that it is lighter during the summer--more pink in it, in other words. It could still be combined with Double Pink KO, but there would be less contrast and the overall effect would be "louder"--which isn't necessarily bad--think of Pappu's famous pics from a couple years ago--that was one loud, beautiful garden. It depends on how comfortable you feel with "loud."

If you go with Munstead Wood, I would tone it down a bit by alternating MW with a white bloomer--like I said above, either Green Ice (lots of nice green foliage when it is between bloom cycles) or Gourmet Popcorn (good bloomer). That would give more contrast, but "neutralize" the overall effect to some degree. And in the cooler spring and fall when MW is darker, the white would keep the darker color from receding too much into the background--one of the problems with darker colors on a back fence.

I guess by dark wine red, what I really had in mind was mums--they come in some gorgeous shades. How do they grow in MI? They bloom for a long time here in September and October. The alternating plants (Green Ice, let's say) would bloom in the spring and summer. I often like to stagger the bloom times of my garden clusters, but then I also like the bigger splash of everything blooming at one time.

Here's a wild idea. My garden center was selling BLACK petunias this year. Get about 3-4 containers of them spread out at the feet of the KOs, and alternate with the Green Ices. That would be really cool. In the spring (before petunias can handle the cold), I'd probably plant a bunch of the darkest pansies I could find. They come a red or purple so dark that they almost look black. For that matter, if it doesn't get too hot during your summers and the pansies can survive therefore your summers (they burn up in July here in Kansas), just go with dark pansie in 3-4 containers alternating with something white like Green Ice. (Yeah--I keep insisting on that white, don't I! : ) ).

Or if you really want all roses, conduct that annual search for the blackest rose possible.

Good luck. Let us know what you come up with. Interesting project.

Kate