I have an Aster like that. I usually cut my Asters down just about now. Those in full sun really grow too tall for the space.

It may depend on the hardiness zone, weather, etc. but I grow Prof. Kippenberg and never have to cut it back here. However, in your situation, I would do so.

In your zone you might have to. I've had my monch's in the same spot for at least seven years now. I've never cut them back or divided them, and they're lush with no staking needed year after year.

I'll cut them back and just call it a test. I did that with a really tall sedum called 'Black Jack' and it worked out fine.

But . . . how much do you cut them back? In half? It will set back the flowering, but I guess that's okay. Will I still get good bloom production?