Allow the unique character of your tree to shine through by thinning it. Carefully.
JAPANESE LACELEAF maples (Acer palmatum var. ‘Dissectum’) are among the loveliest trees in the Puget Sound region. These gorgeous trees thrive in our climate, and their graceful, cascading form brings elegant beauty to the garden in all seasons.
Many homeowners tell me they are terrified to prune their Japanese laceleaf maple for fear they’ll mess up and ruin its appearance. If you don’t prune them, however, they often lose their attractive form and can turn into boring oversized blobs that look more like sumo wrestlers than prized specimens. Also, if the laceleaf maple is growing in a restricted space, left unpruned, it can easily get too large for the area it’s growing in.
Fortunately, it’s really not that difficult to prune Japanese laceleaf maples, as long as you follow some general guidelines. The first is that although it’s fine to lightly prune in summer, the best time for major pruning is in winter, after the leaves fall and the tree is dormant.
Always begin by removing the 3 “Ds”: dead, diseased and damaged branches. You’ll be amazed how much better your tree will look if you simply clean out the unsightly dead branches and twigs. At the same time, remove diseased wood by cutting back to healthy growth behind cankers, galls and blisters to help prevent fungus or bacterial infections from spreading into healthy wood. Remove injured or broken branches by cutting back to a branch or major limb behind the damaged area.
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Perhaps the most important guideline is to resist the drive in all humans to shear your laceleaf maple into a ball or a doughnut. Shearing these beautiful trees ruins their natural appearance and encourages leaf growth only at the end of the branches. Furthermore, this type of shearing blocks air and light from entering the canopy, making the tree more susceptible to disease problems and dieback.
It’s much better to use mainly thinning cuts when pruning your laceleaf maple to bring out the natural beauty. Symmetrically prune out about one-third of the small twigs throughout the canopy. If possible, avoid cutting out branches that are thicker in diameter than a pencil. If a bigger branch must be removed, use a pruning saw to make a clean cut. Never leave stubs: Make sure to cut back to a branch. Not only are they aesthetically displeasing, but stubs usually die and can become infected by diseases that move into live wood, thereby harming the tree.
Finally, remember that once a laceleaf maple has grown too large, it’s almost impossible to drastically reduce its size without causing serious decay and ruining its appearance. If the tree has grown too big for its space, consider digging it up and moving it, or giving it to someone with room for a bigger tree. If your tree is still a manageable size, you can keep it from getting too tall by removing branches that are growing in an upward direction. At the same time, trim side growth and branches that are hitting the ground by cutting to branches farther back in the canopy.
Thinning your Japanese laceleaf maple every winter in this way will bring out the natural beauty of the tree while allowing air and light to penetrate, encouraging increased growth within the canopy. The canopy will have an airy, see-through appearance, allowing the attractive character of the branching pattern to show through.
The only problem with pruning your maple this way is that when your neighbors eye your beautifully pruned tree, they’ll see you as a grand master pruner and constantly barrage you for advice.