I like to let them go a bit past freshly closed. Tho it seems to slow down the flowering. I have found it best to time it about a month before the frost around here. (Early Sept. is when I stop deadheading and start letting selected ones go to seed). If you have the space I say you go girl....I have had some wonderful results and some that I have kept over seven years cause I liked them so well. They have even had sports that I enjoy also. Nothing ventured, nothing gained.