Boxwoods are among the most popular evergreen shrubs used in landscaping, valued for their dense foliage and ability to hold a manicured shape. While some varieties can reach substantial heights and widths, it is possible to maintain these plants at a small or compact size. Success in keeping a boxwood small depends on a two-pronged approach: selecting a slow-growing cultivar initially and consistently applying the correct horticultural techniques. This ensures the shrub remains healthy, dense, and perfectly sized for its intended space.
Starting Small: Selecting Naturally Dwarf Varieties
The simplest way to control the ultimate size of a boxwood is to select a variety with a naturally small size. These cultivars are genetically programmed to remain small, minimizing the need for aggressive or constant pruning. Choosing a dwarf variety means the shrub will naturally put on only an inch or two of growth each year, making maintenance significantly easier.
The Buxus microphylla species, often called Littleleaf Boxwood, contains many of the smallest cultivars. For instance, ‘Little Missy’ is a popular choice known for its rounded, compact form, typically maturing to only about two feet in both height and width after many years. Another classic option is the Dwarf English Boxwood, known botanically as Buxus sempervirens ‘Suffruticosa’.
This slow-growing English cultivar forms a tight, rounded shape that rarely exceeds three feet, making it ideal for low hedges and formal edging. Certain miniature cultivars, such as Buxus microphylla ‘Compacta’, are extremely slow-growing and may only reach a height of 6 to 30 inches over decades.
Pruning Methods for Maintaining Compact Size
Once a boxwood is established, size control relies on specific pruning methods. The two main techniques are shearing and selective thinning, and they must be used for different purposes. Shearing involves uniformly clipping the outer layer of foliage to create a formal, smooth surface, which is often used for hedges or geometric shapes.
While shearing provides immediate shape, it encourages dense growth only on the outer surface, leading to a condition called “shelling out.” The thick outer layer of leaves blocks sunlight and air circulation from reaching the interior branches, causing the inner foliage to drop and the stems to become bare. This bare interior makes the plant vulnerable to collapse if the outer shell is ever broken.
Selective thinning, or structural pruning, is the preferred method for maintaining long-term health and managing size without sacrificing the natural form. This technique involves reaching into the shrub and removing individual branches back to a main stem or a lateral branch. Thinning allows light and air to penetrate the plant’s interior, promoting healthy, dense growth from the inside out.
For heavy size reduction or renovation, the best time to prune is in late winter or very early spring, before the new growth flush begins. Lighter trimming, such as shearing, should be performed after the first major flush of growth in the spring. Avoid pruning in late summer or fall, as the resulting tender new growth will not have time to harden off before cold weather, making it susceptible to winter burn and dieback.
Physical Restrictions Through Container Gardening
An alternative and highly effective method for restricting boxwood growth is to cultivate the shrub in a container. Placing a boxwood in a pot naturally limits its size by restricting the root system, which in turn stunts the top growth. This is a guaranteed way to keep even a more vigorous boxwood variety smaller than its in-ground potential.
To ensure the plant’s health, choose a container that is wide and has excellent drainage, ideally about as wide as the desired mature height of the shrub. Over time, the roots will become tightly packed, which necessitates a specific maintenance routine to prevent the boxwood from becoming completely root-bound and declining. This involves root pruning and repotting every two to three years.
During repotting, the boxwood is removed from the container, and approximately 25 to 30 percent of the outer root mass is carefully trimmed away, along with any circling or girdling roots. The plant is then returned to the same container with fresh potting mix, which stimulates new, healthy root growth and allows the shrub to continue thriving in a confined space.
Containerized boxwoods require special attention during colder months because their shallow roots lack the insulation provided by the surrounding soil. To prevent freeze damage, the pots should be moved to a protected, unheated space like a garage or placed against a sheltered wall and covered with a thick layer of mulch or burlap. This protection ensures the boxwood survives the winter and maintains its compact form.