|Clematis montana in a client's yard taken in May.|
Large flowering types that include Henryi, Nelly Moser and Ruby Glow open in spring on old wood and can grow 10 to 12 feet. They make excellent choices for covering a large area. They produce large flowers in late spring and smaller ones later in the season. Trim weak and dead stems back to a set of strong buds. Cut back remaining foliage and tie the plant to a structure or support to prevent it getting all tangled up in summer.
The third group, and the easiest to care for, includes favorites like Sweet Autumn clematis, Jackmanii, Betty Corning (one of my favorites), and Ville de Lyon. To keep plants full and lush, cut the stems in spring to within a foot of the ground, leaving just two to four sets of buds per stem.
Remember all clematis like shade on their roots so a good covering of mulch helps. Add some lime if your soil is acidic as they like a slightly alkaline soil. (Ph of 7 - 7.5 is about right).
If you are not sure when to prune and you know the name of your clematis send me an email as I may be able to help you.