Yes. Pinestraw hinders re-seeding of most plants. How about verbena? There are some great verbenas that would be super with the knockout rose. They handle heat and drought, and you can get some lovely white, pink, purple, magenta...different kinds. They are perennial for us!

GGG

Thanks GGG! Verbena does seem to do well in our heat, too.

Bama,

I have oregano, parsley and lavender around my Knock-out roses (7). Those herbs don't grow over the roots, but it may be too hot for lavender in your zone. I also have a few clematis, but am training those up on the fence instead of on the roses. I used a composted mulch around mine, but they grew so quickly in just one season that I can't even get under them to mulch now.

What color are your roses? Coreopsis 'Moonbeam' is a great yellow with frilly foliage. While it's late to emerge each spring here in my zone, it blooms continuously until frost. Saliva 'Marcus' is a gorgeous 8" high purple/blue perennial salvia that blooms all summer and goes great will almost all other colors. If you can find a short nepeta (around 12-15" high), that gives a similar look to lavender and it makes a beautiful mounding billow. A little goes a long way. You can usually divide nepeta after one good growing season.

Cameron

I use pinestraw and have never had a problem with reseeding. How about a creeping/trailing lantana?