The two varieties I have bloom in colors of pale blue and soft white in late spring and throughout the summer. When their blossoms are spent, I trim their stems down to the base of the plants and it isn't long before new blossom stems appear and they're once again in full bloom. These flowers do need to be staked, as their stems are very fragile and delicate and their many blossoms tend to weigh them down. I also enjoy them because they are very disease resistant and are a hardy perennial in our USDA Zone 6. The Campanulas grace the flower bed between our two patios and are situated next to several clumps of charming Colorado Columbines that also produce delicate blue and white blossoms.
Butterflies also enjoy imbibing nectar from the mum blossoms throughout the summer.
There are many more flowers, shrubs, and trees that grace our back yard now as opposed to what there were ten years ago. However, in this brief article I've only highlighted some that are the most attractive to butterflies and hummingbirds. Again, this entire area was all bare, non-fertile dirt AND rocks when we first moved here. Its velvety blossoms bloom in fragrant clusters at the tips of its graceful branches from May through September. As soon as the first blossoms are spent I remove them.