I live in zone 5 (NE Wisconsin) & planted 2 wisteria on my new pergola in 2007. It's growing nicely (& bloomed, last year & this) but I am wondering about pruning it at the bottom. It keeps sending up new shoots and I am thinking I don't want it to get all bushy at the bottom. Generally though when one prunes back, doesn't that encourage branching? Advice please?