Certified GKH Gardening Expert
Heavy pruning should only be done when there are signs of new growth for the year. Cutting them to the ground before this can kill them, as they have no nutrient storage through the winter. Since they won't be growing vigorously through the winter, they need all of the nutrients from those leaves.
This article will help you to prune the plants:
Here is an article to help you with their general care: