Pruning Japanese Maples
The right cuts reveal a branch pattern that looks good with leaves or without
Japanese maples are elegant in all seasons, with delicate leaves, fine fall color, and the loveliest branch patterns in the world. The two most common forms of this tree are the upright, understory tree (Acer palmatum and cvs.) and its little brother, the Japanese laceleaf maple (Acer palmatum var. dissectum and cvs.), a much smaller, weeping tree often used as a garden focal point. When planted in the sun, as opposed to a partly shaded understory, these trees become fully foliated rather than open and airy. Some simple pruning can restore or enhance their natural form, bringing the most out of them for summer and winter viewing.
Japanese maples less than 15 years old are prone to put on new growth that looks like a buggy whip: unattractively skinny with no side branches. This problem is exacerbated by pruning, often done by the impatient tree owner hoping to create an open look sooner than nature intended. Shortening or removing the buggy whips only stimulates more of the same. My best advice is to leave the tree alone for as long as possible. You will be surprised to find that, as the whips age, they fatten up, develop lateral branches, and turn into nice-looking scaffold limbs. Trust me. Sit on your hands and wait to start the thinning process until after the tree has aged and developed some grace.
Another practice to avoid is attempting to restrict the height of a Japanese maple. It won’t work. The tree will simply grow faster with thin, unruly branches. The width of these trees, on the other hand, can be somewhat modified.
Enchanting Japanese Maples
Timing isn’t everything
The old gardener’s adage is “Prune when the shears are sharp”—and in general this is true. If you prune selectively, almost anytime is the right time to prune a Japanese maple. With that said, these maples are most easily pruned in winter or summer.
With the leaves out of the way in winter, it is easy to see the branch structure and, in turn, make the right cuts. In summer, however, you can judge the right amount of thinning needed to see the tree’s bones. Summer pruning also stimulates less plant growth than winter pruning, so you can get away with a little more and the tree will stay thinned out longer. I avoid pruning when the temperature is 80°F or higher, especially when the plant is located in full sun. Removing foliage will expose the tree’s thin, previously shaded bark to the light, inviting sunscald.
To avoid causing stress or stimulating unsightly growth, never remove more than one-fifth of a Japanese maple’s crown; you should also not prune a branch that is more than half the diameter of the parent stem. In addition, don’t remove more than a quarter of the foliage of any given branch. Each branch is fed by its leaves through photosynthesis. Removing too much of the foliage will starve the tree of nutrients.
If you prune selectively, almost anytime is the right time to prune a Japanese maple.
If you are going to “limb up” your tree by pruning the lowest branches, avoid stress to the plant by removing only a few at a time, not many at once. Never make one cut directly above another or opposite another limb being pruned off in the same year. That might cause decay to coalesce inside the trunk.
The trick to making Japanese maples look great is to separate the branches into overlapping layers that don’t touch each other. Most single-stemmed plants have a series of scaffold branches that radiate in a roughly spiral fashion up the trunk. If a lateral branch from any of these scaffolds grows downward, crossing into the layer below, it should be removed or cut back to a side branch facing up and out. This is how the tree becomes layered, like a series of fans.
While the average tree can handle light pruning, all cuts wound a plant. If your maple is in poor health, make minimal cuts or limit yourself to deadwood removal. To be extra kind, avoid pruning during the tree’s low-energy times: just as leaves emerge in the spring or when leaves are dropping in the fall (just two weeks in each case).
Upright Japanese maples
When pruning a Japanese maple, cut up to—but not into—the branch collar. If you cut too far out, you will leave an unsightly stub. If you cut too close to the parent stem (a flush cut), a column of rot will enter the stem. To minimize stress, dieback, and regrowth, do not remove a side branch that exceeds half the diameter of the parent stem.
You can’t change their nature
Some Japanese maples do not have especially graceful branches, possessing instead a twiggy or stiff-looking internal structure. Pruning cannot change the essential character of these trees. The wise gardener learns to appreciate plants for their own attributes and remembers that a good pruner can only reveal beauty, not create it.
Laceleaf Japanese maples
Many gardeners are so intimidated by this tree’s fragile branch structure that they don’t prune it at all, letting Japanese maples turn into mounds of foliage that resemble Cousin It. Others use such a heavy hand that they wind up with a little ball of foliage on the end of a stick. Laceleaf-maple pruning is often called “shell pruning” because when done correctly, the top layer of branches forms a protective veil of foliage over the plant that resembles a shell. Because the bones of this tree are important to its overall beauty, you’ll want to keep many of the unique, twisting branches intact.