How much should I prune my clematis, and when?
Best time to prune clematis is just after flowering. As to how much, depends on how established the plant is, I've cut well established plants back to just above the ground and they come back stronger than ever. If you don't have many shoots you can cut them back to a few buds then the plant will produce a lot more shoots the following season. In my opinion as a pro gardener you won't do any damage to a clematis by any amount of pruning. Just keep the dead twiggy stuff out and prune to restrict.