I attended Dan Gilchrist's seminar at Swanson's Nursery about pruning Japanese Maples. It's amazing what you can get for free these days. I took in so many ideas, but the primary notes that I took are:
- Help the tree become the shape that it wants to become.
- Be aware of air flow and sun between/throughout branches/leaves.
- Don't hurt the collar tissue; create "belly buttons."
- February and March are the best times to prune, before buds form. Otherwise, June through August is good so that you can see the leaf clouds and direct their formations.
- To train/redirect energy from one branch to another, the branch that you want to keep must be at least 1/3 the width of the branch you want to cut otherwise you'll get "the fright" - a whole bunch of smaller branches rather than redirecting the growth into the intended branch. You may need to aim to keep a lower branch that is wider if the upper branch is too small.
- By keeping trees pruned decrease chances of disease and bug infestations.
General guidelines for pruning:
- Health - remove broken and dead branches.
- Aesthetics begin inside/out, bottom/up and keep moving around the tree as you prune.
When you (and the tree) consider what shape to aim for think about the perspectives that people will see the tree from: is it on a rockery and will be seen primarily from below? is it in a corner? is it in the middle of a courtyard that exposes all of its sides?
Also, consider how you want the leaf clouds to form. Think about how the tree will fill out and where you want to direct growth.