We don't experience your weather conditions here, needless to say, but Campanula portenschlagiana is indestructible across a wide range of conditions as well as being considered somewhat invasive. (This latter characteristic is more of a consideration in rock gardens, where it is often quickly too much of a good thing.) Aubrieta hybrids and cultivars are not as tough, in my experience here.
When I hear the word "invasive", I don't walk, I run fast the other way. So, I am afraid to take chances on that one.
I know nothing about Campanulas other than I think they are beautiful. I have been looking at Bluestone Perennials because I think it's informative. They have two others that I "think" my work. I would like your opinion on these:
1. C. porcharskyana
2. C. cochlearifolia
3. OR do you have another suggestion?
4. Or do you think I should go with C. portschlagiana?
Well, I'm a big fan of Campanula, though I do avoid the more invasive ones! C. cochlearifolia is also one of the spready ones, like C. portenschlagiana. C. poscharskyana is supposed to be less vigorous but still spreading (I don't believe I've grown this one which must mean I never came cross it in the stores here... Though it is widely grown).
If you really want to avoid any that might spread, you might consider tap-rooted species, e.g. C. carpatica... ?
Thanks alta, I have picked some fairly "tough" Campanulas, I think. I have never had any Campanulas even though, I love the way they look and would like to grow some. I worry that my hot, humid climate will just "melt" campanulas. So, that is why I picked the above mentioned. On the other hand, man, I don't want to plant a nuisance.
I want these plants to grow around stepping stones and hang over a terraced paver wall. I would put these plants in the area/s that have shade.
Birder17, did you go with a Campanula? Which one? I have one that's great but I can't remember which one it is! It spreads but not too fast and is easy to remove.
I just wanted to mention that in my 6b climate, which has cooler temps and lower humidity in the summer than you do, Aubrieta is carefree except for a haircut after blooming, non-invasive, and stays in bloom a long, long time. It blooms earlier than the campanula. If you ever feel like trying it, I'd love to know how it behaves for you.
Pics are taken today. On left are aubrieta, pic on right is campanula.