In the beginning of winter, remove spent blooms from the clematis plant using sharp and clean garden scissors. Remove everything down to where the blooms meet the stem of the plant. Once the air temperature comes down to 25 degrees Fahrenheit, cover the base and crown of the plant with a thick layer of mulch. It is also acceptable to use straw, hay, manure, leaf mold or grass clippings for this purpose.
Healthy clematis plants can spend the entire winter in pots as long as the pots are at least 2 feet in diameter and are suitable for freezing temperatures. In this case, gardeners don't need to cover the plants with mulch. However, if the container is not made for low temperatures or if the plant is not in a good condition, store the plant somewhere where it is not going to freeze, or cover the plant and the container with mulch.
To cover the container, place some old tree leaves in large bags, and arrange the bags around the pot once it freezes. Once the plant has frozen, it is important to make sure that it stays that way until the spring. If the clematis plant thaws and then freezes again, it may die.