I grew the tall kind, c.'Rose Queen'. I would start deadheading them in July. The first couple of years I didn't and they were over 5 ft tall. When I started dh them, they did get bushier and with that there were more flowers. Careful of the thorns though. With mine, I'd put a peony cage over them. Mine would tend to lean when they got really tall and that would help support them. They really reseed too!
Enjoy!

Kat

I don't pinch them....I like them tall and find that they get bushy without pinching.
You can also grow a shorter variety is you prefer them not so tall.
Linda C

They get bushy without deadheading, but I've found they get even fuller when deadheaded. I only had 3 plants and it would look like a sea of pink flowers outside my window. :)

Kat