Pruning is a matter of whacking away. Keep in mind Ys. Anything pruned can be easily rooted. If it is above a Y, it will bloom much faster. If you have to cut a stem below a Y, then stem growth and branching will have to happen so as to make a new Y.
Mine are getting too big to get in my basement for storage. I will be chopping them this winter.
I have found a lot of useful information at this site:
http://www.trumpetflowers.com/...
Lots more info here:
http://www.brugmansia.us/index...
You might also stack them at a 45 degree angle in the GH so they will fit. Roll them 45 degrees periodically so growth is not messed up and to assist in moisture in reaching all the soil.
