Pruning Japanese Maples
Many gardeners are afraid to prune their trees and shrubs. All Japanese maples need some pruning, especially when young to help establish their structure. Lace leaf maples need more pruning than other varieties to keep them looking Japanese instead of a big red or green, shaggy mound. Pruning should thin out the number of smaller limbs and open up the tree structure for air flow. The ideal look for a lace leaf maple will allow the viewer to see some of the structure of the trunk and bark as a contrast to the beautiful lacy leaves that flicker when the wind blows. The best time to prune your maple is in the spring when the tree is just forming buds. Remember the new growth will add another twelve to fifteen inches to each limb during each growing cycle. For weepers it is the weight of the new growth on a young branch that causes the weeping effect, so annual pruning of young maples is recommended to help establish their shape. Don’t be afraid to prune–remember its like giving your maple a haircut [but not a bowl cut]–it will grow back.
When pruning upright maples you want to remove branches from the inside that crossover. If you have a ‘V’ shaped trunk the inside crossover branches are those growing inside the ‘V’. If you collect JMs you have probably noticed that most JMs grow in the ‘V or vase’ shape.
Additionally, customers send me photos of their maples and ask about 3′ of new growth that stick out from the structure of the maple. The key is not to let these branches get that long. Prune these branches at about 8 to 10 inches from the main structure of the maple, don’t let your maple spend its energy growing something you don’t want. This also applies to branches and leaves originating below the graft. Below the graft is root stock which is usually a green leaf seedling. Always remove this growth.
Important tip: Use rubbing alcohol and not bleach to sterilize your shears when you prune. I carry a small jar with a lid and regularly dip my pruning blade into the alcohol to keep it sterile. Also, the alcohol evaporates quickly from the blade. Bleach on the other hand can irritate the cambium layer of the maple. Using rubbing alcohol to sterilize your pruning shears helps to prevent the spread of disease from one plant to another.