The seeds will be ripe when the pinkness of the seedheads has fully changed to tan, and the heads are starting to break up. The easiest ready to tell if the time is right is to hold a few seedheads over an open paper bag, and shake them gently. If they fall off into the bag, they're ripe.

I've only winter sown Muhly, and it worked great. You could, however sow them in situ, in late fall. You'll no doubt lose some to rain washing them away and birds eating them, but some will germinate in the spring. In your zone, you may not have to bother sowing them. When I was growing Muhly, I got plenty of volunteers.

Thank you very much, donn. I searched the web for a couple hours and did not get as good information as you just gave. I will be sowing them in pots for certain. I did find several sources on the web that said to sow them in spring after the last frost. I assume that I should put several seeds to the pot?