I used Campanula glomerata over numbers of years and found it by no means the most invasive of horticultural bellflowers.

It is, however, one of those perennials you have to keep on top of (reducing as needed).

I'd never plant C. punctata or C. takesimana, which are extremely difficult to control, anywhere. I also feel that our own mixed perennial garden is too small to take any chances with things like C. glomerata.

Perhaps some of the cultivars of C. glomerata are less vigorous. We've had C. glomerata 'Superba' and 'Purple Pixie', both of which just died away.

Never have had a problem with glomerata, but as sunnyborders just said I DID make the mistake of getting punctata years ago and it is beautiful in bloom, but takes over and I cannot get rid of it.

I used to have a big garden out in the backyard for veggies...like 30 x 60. Well, the kids moved out so I started planting flowers in that garden. OOOOh did I love those C. glomeratas, and they spread! Well, the voles got into a bunch of the garden, so I mowed it ALL down and threw in grass seed and that was hmmm 10 years ago?! I am STILL mowing C. glomerata leaves every week. They never bloom cuz they never get over 4-5 inches tall, but this year I noticed the area has enlarged by 20%....probably been sneaking an inch or so. every year. Time to spray it with 24D or something. So be careful planting it, or else consider yourself forewarned.

I have the glomerta and though I enjoy it at this time of year it spreads too much for me. I'm not able to get rid of it without tearing up whole beds so every year I dig out as much as I am able. Nice plant, but I'll have it forever--like it or not