Answer: In the late fall, after a frew frosts or freezes, top up the mulch around the plants so it is three to five inches deep. Do not allow it to touch the stems of the plants. That is all you would need to do for winter preparation. Clematis are very cold hardy plants.
Most clematis do better in the long run if trimmed back to about a foot tall in early spring their first year. This helps them develop a sturdier framework of stems. After that, annual pruning depends on which variety you are growing. (Some gardeners prefer to start immediately with the normal pruning routine and skip that first hard pruning.) None of yours would ever be cut down to four inches.
The Jackmanii blooms on new growth so is usually cut back to about two feet in early spring when the buds are swelling. Remove all winter damage and cut just above a swelling bud.
Niobe, Will Goodwin, and Piilu bloom on the older growth so are pruned very lightly in early spring, cutting just above a swelling bud and removing any winter damage, usually only removing about 6 inches or so.
Clematis normally grow very slowly their first year or two and begin to bloom better the third year once they have become well rooted and established. Enjoy!
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