Boxwood are everywhere in the Lexington landscape. Nonetheless, I’ll bet you haven’t been properly introduced. What do you really know about this familiar neighbor?
First off, you might not have your neighbor’s name quite right. Boxwood refers to both a singular shrub or a bunch of them. There is no such word as “boxwoods,” though I, and probably you, have been known to add that pluralization. They are so named because the young stems of some species of boxwood are four-sided and thus are square in cross-section, like a box.
As traditional as these plants have become, they actually originated from other parts of the world, such as Japan, southern Europe, northern Africa and western Asia. Fossilized boxwood plants date back more than 22 million years. In the first century B.C., wealthy Greeks and Romans landscaped their villas with boxwood topiaries and used the wood for utensils, tablets and ornaments. Nathaniel Sylvester, the earliest European settler of Shelter Island, N.Y., planted the first boxwood in the U.S. on his plantation in about 1653.
Now, before you invite them to your home, you might want to know more about their dietary preferences. Boxwood do not like compacted or poorly drained soil. They will grow in a wide variety of soil types as long as the pH is alkaline or slightly acidic, say 6.5 to 7.2.
Boxwood will take full sun to partial shade and are quite drought tolerant once established. However, they have very shallow roots and so mulching is important, both to protect the roots and to maintain soil moisture. Don’t mulch too deeply, just an inch or two is fine, and keep the mulch away from the stems.
While boxwood, treated properly, can be a tough shrub, overwatering and over fertilizing stresses them, as can improper pruning. Too much stress will weaken any plant, making it vulnerable to insects and disease. Boxwood are prone to leaf miners, mites and psyllids, and to various fungal diseases.
Most boxwood in the home landscape are pruned both to maintain size and to keep that roundish shape that many of us are used to and therefore find attractive. To reduce size and attain that visually pleasing form, you’re pretty much stuck with using garden shears. But shearing promotes compact, twiggy growth and also cuts the leaves, making them unsightly. Every time you shear, one branch becomes many branches, eventually making the shrub so dense that light cannot penetrate and air cannot circulate. This results in the ideal environment to promote disease.
To increase air circulation and let light penetrate into the interior of the shrub, boxwood need to be thinned on a regular basis. This thinning goes a long way to repairing shearing damage. To thin boxwoods, simply reach into the plant and snip out stems, removing them evenly throughout the entire body of the plant. On a small boxwood, you might remove stems 2 to 4 inches long. On a boxwood 1 or 2 feet wide, pull stems about 6 inches long. Larger shrubs will usually look fine with stems up to 8 inches long pulled. Refrain from cutting the stem back beyond its last set of leaves. Typically you should aim to remove about 10 percent of the branches. After completion the shrub will have small holes all around its outer surface, and you’ll be able to see the interior twigs when you peek through them. The surface of the shrub will look and feel looser and it will also look somewhat irregular and more natural. At the same time, check out the interior of the plant and remove any dead wood.
Do not prune in August through October. Pruning encourages new growth, so if you prune too close to winter weather, that fragile new growth might be damaged and look unattractive. If boxwood need pruning in the spring, I wait until after that first flush of spring growth since the shrubs will then maintain that desired form for longer. The ideal time to prune and thin is in the winter when the shrub is dormant.
Of course, not pruning to reduce size or to maintain a rounded form is perfectly fine, so long as you have selected a boxwood with an ultimate size that fits the space and if you enjoy that natural form. It is likely that minimal pruning and shearing is better for the shrub. However, thinning is always advisable.
There are about 30 species of boxwood. American or common boxwood (buxus sempervirens) and littleleaf boxwood (buxus microphylla) and their many cultivars are the primary species used for ornamentals. How to choose the right ones for your garden? Know your site then do some research. I recommend the book “Boxwood Handbook: A Practical Guide” by Lynn R. Batdorf, the curator of the boxwood collection at the United States National Arboretum.
So the introductions are done. It’s always nice to get to know your neighbors.