Are you sure you don't want something taller behind the roses? You could plant some blue and purple sages, they would complement the colors of the roses.
Renee

Renee, this spot is sort of tucked in between the back fence and a path behind the roses; it's not part of the rose bed at all. It lies about 8-10 feet behind the roses.

Maybe a mass planting of Helleborus argutifolius, the Corsican Hellebore. Lovely foliage, flowers are green and in winter when everything else is sort of meh, it is going full-tilt. Tough plant. Probably shorter in your inland area than near the coast.

Here is a link that might be useful: Corsican Hellebore

I love that plant! I read that it requires lots of water- constantly moist soil. Have you grown it, Hoovb? Do you know where to buy it?
renee

Does it require lots of water? Mine seems happy with dry shade. I got mine as a 4" native sons pot from local garden center.

I can send you some seeds when it blooms.

Hoovb, thank you for your suggestion. I completely forgot I asked this question, and found it while searching again. :-/

Here's a photo of the area, taken May 2011. The blank slate I want to design is about 9x9', in the corner between the tree trunks. The roses in the foreground are separated by several feet. A compost pile had been there for a few years so the soil has a nice top layer of compost.

{{gwi:557198}}

I'm considering a few possibilities:
- One large Hybrid Musk rose (Darlow's Enigma - I've grown it before in a smaller spot and had to give it away - it loved the shade.
- Flagstones surrounded by smaller plants, leading to a bench in the corner.

This corner is not highly visible from the patio or house, but it is the view from our bedroom window and we'd like it to look nice.