Japanese maples, with their delicate foliage and vibrant seasonal color, are highly prized landscape trees. While some varieties naturally grow large, it is possible to maintain these plants at a size significantly smaller than their genetic potential. Keeping a Japanese maple small requires understanding its growth habits and consistently applying specific horticultural techniques. These methods allow gardeners to control the tree’s height and spread, making it suitable for compact gardens, patios, or container specimens.
Choosing Naturally Smaller Cultivars
The most straightforward method for keeping a Japanese maple small is to begin with a cultivar genetically predisposed to limited size and slow growth. These varieties, often labeled dwarf or semi-dwarf, have a reduced growth rate, typically adding only 3 to 12 inches of new growth annually. This foundational choice minimizes the need for heavy, size-reducing pruning later in the tree’s life.
Look for cultivars with the term dissectum, which refers to the weeping, finely cut leaf types that are generally smaller and slower-growing than upright varieties. ‘Crimson Queen’, a weeping laceleaf variety, typically reaches a manageable height of 4 to 6 feet with a wider spread of 6 to 8 feet. For a more upright, bushy form, ‘Mikawa Yatsubusa’ is an excellent choice, growing slowly to only 4 to 6 feet tall and 3 to 4 feet wide over its first decade. Selecting naturally compact trees reduces maintenance and stress on the plant.
Pruning Techniques for Size Reduction
Pruning is the most direct way to control the height and width of a Japanese maple, but it must be performed with precision to maintain the tree’s health and aesthetic appeal. The two main types of cuts are thinning cuts and reduction cuts, both serving distinct purposes in size management. Thinning cuts remove entire branches back to the main trunk or a larger lateral branch, opening the canopy for air circulation and light penetration. This includes removing the “three D’s”—dead, diseased, and damaged wood—as well as branches that are rubbing or crossing.
To actively reduce the size of the canopy, a reduction cut shortens a branch by cutting it back to a smaller, healthy lateral branch or bud. This technique, also called a selective heading cut, transfers growth energy to the remaining side branch, directing new growth away from the cut. The remaining lateral branch must be at least one-third the diameter of the removed portion to prevent dieback and stimulate healthy redirection. Always make a clean cut just outside the branch collar, the slightly swollen area where the branch meets the trunk, as this area facilitates rapid wound healing.
The timing of pruning is determined by the desired outcome, with heavy structural reduction best performed during the tree’s dormant season. Late winter or early spring, before the buds swell, is ideal because the lack of foliage allows a clear view of the structure. Lighter, more detailed maintenance pruning can be done in mid-summer, as the leaves help visualize the tree’s final shape. Regardless of the season, remove no more than 20 to 25 percent of the live canopy in a single session to avoid stressing the tree.
Keeping Japanese Maples in Containers
Growing a Japanese maple in a container is an effective way to restrict its size, as the pot’s volume directly limits root system growth. A containerized tree can be maintained at a fraction of its natural size, provided proper environment and care are given. The container must have excellent drainage holes, as Japanese maples are highly susceptible to root rot in waterlogged conditions.
The potting medium should be highly aerated and well-draining, avoiding standard garden soil which compacts easily and retains too much moisture. An ideal mix often consists of pine bark fines, perlite, and a quality commercial potting mix, with coarse materials promoting fast water movement. Because the root system is confined, containerized maples require more frequent watering than those planted in the ground, often needing water several times a week during summer.
To keep the tree healthy and prevent it from becoming pot-bound, long-term container specimens require root pruning and repotting every two to three years. This process is best done in late winter while the tree is dormant, involving the removal of the outer 1 to 2 inches of the root ball, including circling or matted roots. The tree is then returned to the same container with fresh potting mix, which renews the soil’s nutrient content. Container maples are more vulnerable to winter cold; in colder climates, the pot should be insulated or moved to a sheltered, unheated space to protect the roots from freezing.