Just out of curiosity, what happens if you don't trim the roots back? I just tried doing mine last week and I pulled out a good twelve footer. Got me wondering if I was hurting production by doing that. The big concern I had was the varieties intermingling, but I couldn't decide if intermingled feeder roots had any impact on that.If you don't trim the roots back they will take over your yard. You're not cutting near the main crown so it doesn't hurt the plants at all. The roots can grow 2 or 3 feet per year in every direction, then you start having sprouts coming up all along those roots. I guess that's fine if you have all the room in the world, but it would also make it very hard to trellis the bines if they cover an area 5 or 6 feet in diameter per plant.