There is a very large evergreen clematis starting to devour my detached garage. How far back can I cut this and when should I prune it back? It’s one of the first early spring bloomers with white flowers, possibly armandii? But I am uncertain…I need help since I don’t want to butcher it and lose it, but it needs a big haircut!
Clematis armandii does have the reputation for taking over the world. According to the American Horticultural Society’s Practical Guide on clematis (Clematis, by Charles Chesshire, 1999),
you can prune it AFTER is has finished flowering, which in Seattle, it normally does by the end of March. While this type of clematis can be pruned in late winter, it flowers on the previous year’s wood, so pruning at that time may remove buds and prevent flowering that spring.
Step 1 – remove any dead, dying, damaged, or deranged shoots.
Step 2 – they suggest that no real pruning is necessary but you can cut it back to control its growth. But you do NOT want to cut it all the way back into old dark, woody growth.
Prune directly above a pair of strong side shoots.
Step 3 – you will need to keep after it each year to avoid a build up of tangled growth.
Fine Gardening has an article by Lee Reich on pruning clematis here.