All clematis like a slow release plant food like Osmocote in the spring, right when you see new growth sprouting. Just work the Osmocote into the top inch of soil following the instructions on the package. The right time to prune a clematis depends on when it blooms. Early flowering clematis like Montana should be barely pruned at all but pruning is best right after they finish flowering. Always remove dead wood but the less you prune the more they bloom. Then there are the group two clematis that flower in early summer. These need medium pruning by shortening the vines by 8 inches in March. The group two clematis flower on both old and new growth. The third group is the late bloomers that flower in late summer and fall. Prune these back hard in March so they are just 3 feet tall. Then you get lots of new growth and flowers. To sum it up, prune most clematis in March, the late bloomers getting more cut off than the early summer bloomers but don't' prune the  very early flowering clematis until after they finish flowering. Keep growing, Marianne Binetti