I planted a border of deep blue and white campanula's this summer. They are blooming beautifully. My question is: what do I do at the end of the season? Do I cut them back to ground level? Thank you

I can invision your border and I'm sure it's beautiful!

If you pick off the flowers as they fade, it will encourage longer flowering.

You probably won't have to worry about this until after the next growing season, but you will probably have to divide them next Autumn or spring of 2004. They multiply quickly and if not divided they might become crowded which would be unhealthy.

I would recommend to allow the foliage to die down until it's all brown. I don't know where you are or how cold winters get, but once everything goes dormant/dies back, it would be safe to clean up the dead leaves.

I usually just leave my flowering plants until very early spring, and before they start to grow again I clean away all of last years stuff.

I have campanula growing in my yard. These plants self-seed. Every year the bed gets larger and larger. I usually cut mine down to ground level in the fall during cleanup. Next year, I have to thin out the plants because soo many come back up. Even our neighbor is growing this plant from volunteer seed that blew into their yard.