Shirley,
I cut mine back to about 2 ft tall, it is necessary for me to put up the temp greenhouse. They are usualy touching the top by the time I take it down in late March. They get over 12 feet tall over the summer.
I would only cut back the mushy part for now.

pa

Thanks PA. If they grow that fast in the spring then I'll cut back as needed and not be concerned. I want it to get gigantic like some I see around the neighborhood here. They are enormous and even with the big freeze and die back last year they grew to be about 9' high and as big around by the end of the summer.

Shirley only cut the part that needs cutting.. You want to keep as much growth above a Y to ensure loads of blooms..

Kylie