Laceleaf 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 palmatumvar. 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.