Wow! You have had a frost already? Montana had a snowstorm that dumped 4 feet of snow at the end of September. This morning I was 42° and now at 12:30 p.m., it is a bone chilling 95°. Supposed to be 97° today, I can easily see that happening. Here are some sites to help you out.
Enjoy the cooler weather! 🌞
Cut the plants back to the ground at the end of the growing period when the foliage turns brown, usually in early fall for cooler climates and late spring to early summer in warmer climates.
Just let die back naturally.
Here's a post that might help - https://www.familyhandyman.com/painting/how-to-age-wood/#targetText=Here's%20how%20to%20age%20wood,t%20have%20to%20be%20precise.
Hi Joanne, I leave them until spring, they reseed themselves