Did you want these as permanent fillers or new each season? The blue flax is a perennial. Verbenas could be nice. I've used the bedding begonias a time or two with success.

Diamond Frost Euphorbia will give a nice airy appearance. It tolerates heat. If you just want something to cover early, try pansies or violas.

Almost any plant will take some nutrients, so modest supplemental feedings wouldn't be out of line.

Either annuals or perennials would be fine. Mainly I was just wondering if people had any good or bad experiences with anything they planted with their lilies in containers. I like the look of flax, haven't had any in a while. It is possible, though, that they might want to take over... I seem to remember that the little patch I planted did become a big patch of it in a few years. Still, the notion of white lilies surrounded by clouds of blue does capture my interest.

Hmmm... I think whatever does go in there, I would like it to stick around for a good part of the growing season. I love pansies and violas, but very shortly, they'll be blasted by heat, I'm sure. I tried keeping some lovely pansies going through the summer one year, but they kept frying and getting aphids, so it wasn't successful.

Going to go look up Euphorbia now...