The house we bought (Zone 5) 3-1/2 years ago has 3 wisteria that I would guess to be 5-10 years old. The first year there were no blooms on any of them, but the last two years two of them have bloomed. I know that they need to be pruned regularly but I have no idea where to start. One planting (actually I think there might actually be three plants in this one location) is at the top of an 8' gabion wall and it spills over; one is planted in poor soil at the top of a 6' cement retaining wall (a really ugly wall that runs down our driveway); the third is planted in a fairly shady shrub bed that is pretty "wild" and there is no support there -- it is starting to clamber up trees and shrubs. If I prune now will I be cutting off this year's blossoms? Where do I start? What harm can I do?