To grow this plant into tree form, simply drive a stake into the ground very close to the stem, making sure to not damage too many roots. The stake should ideally be 4-5 feet tall. This will allow you to support the tree as it grows and train it to grow straighter than it would naturally.
The best time to do this pruning is just after the plant goes dormant to minimize any stress on the plant. Some pruning will need to be done during the growing season as well, but doing the majority as the plant is dormant is recommended.
Prune all branches, buds and leaves along the stem, leaving the tip of the plant and any leaves using a quality set of pruners. Removing all of them will force the plant to grow upwards. Remember, removing any branches, leaves, and buds that are growing along the stem will ensure no branches form lower than the desired height. Support the plant along its length by using twist ties or using landscape plant ties. Support the tip also, remember, you are training the plant to grow upwards until your desired height is achieved. At that height you will find pick a branch and leave every branch above it to grow. These branches will form the canopy at the height you chose.
If you receive your plant before or during the growing season, light pruning throughout the growing season to control the number and lengths of branches forming lower than desired is suggested because removing all the branches and leaves during the growing season will affect the plants ability to feed itself. Once the plant goes dormant, removal of those lower branches, leaves and buds can begin. As the next growing season begins, the plant may once again develop leaves along it stem if you missed a bud or two. It is fine to leave them until the plant once again goes dormant..
Once the plant has reached a good height, I like 5-6 feet, you can leave a branch or two to grow and begin to form the tree shape. Don’t go too wild on pruning the branches once it has reached the desired height, they can be pruned at a later date if needed. Occasional removal of leaves and buds may need to be done along the stem to keep your new Japanese Maple tree looking great.