Hedge and clipped plants are important elements in all but the most ‘natural’ of gardens. They may be larger screens and windbreaks, turning the garden into a sheltered haven from the outside world. They may also be smaller elements, separating one part from another, edging beds, or creating patterns and trimmed accents. For these smaller elements, plants that will grow in a wide range of light conditions, and that clip easily need to be carefully chosen. For its small foliage, dense growth, and tolerance of many conditions, the American Boxwood is always a top choice.
The name of this plant is a little odd, because it is not, in fact, American. It is a European plant, that was brought over by the early settlers. They considered it a vital garden plant, and the formal gardens it was used for were the only garden style they knew. This boxwood was a European plant, that grew wild from Britain to Morocco, and over into Turkey, as well as in all gardens. Today the English call it, ‘common box’. Those first boxwoods were planted in 1653 on Shelter Island, which is part of Long Island, N.Y. at an estate called Sylvester Manor. The plants were shipped across the Atlantic, from Amsterdam.
About 100 year later the botanist Linnaeus would describe a form of boxwood that is much smaller, that today we call ‘Suffruticosa’. This became the most commonly grown type in Europe, and the plant we today call ‘English boxwood’. This plant is useful for very low hedges and edging, up to perhaps 18 inches, and as low as 6 inches. The American Boxwood is suitable for low hedges too, but it can also be used for taller hedges up to 10 feet tall.
American Boxwood – Buxus sempervirens – is a broad bush, wider than it is tall, that can eventually grow to 20 feet tall, and even into a small tree as much as 30 feet tall. That takes many decades, and we usually see this plant, even if unclipped, as a rounded bush no more than 10 feet tall. Young plants, once they are established, can grow as much as 12 inches in a year, with good care, so it doesn’t take long to create hedges up to 3 feet tall, for bordering parts of the garden, or for making low, enclosed areas. The growth-rate varies a lot between varieties, with some growing only 3 to 6 inches a year, and others growing up to 15 inches a year.
The young stems are square, with slightly ridged (winged) corners. The bark is smooth and greenish when young, turning yellowish and rougher as it ages, and then becoming light-brown, with some ridges and grooving.
The leaves are oval to oblong, between ½ and 1 inch long, and ¼ to ½ inch wide. The tip has a small notch in it. The upper surface is shiny and dark green, and the lower surface is also shiny, but light green. Some varieties have larger leaves, and leaf size is also affected by clipping.
Boxwood has separate male and female flowers, but on the same plant. This is called monoecious. They are similar in appearance, with pale green petals, and yellow stamens carrying the pollen. They are fragrant, and they will mostly be seen in April or early May on older, unclipped plants.
A small seed pod, one-third of an inch long, with six points, is sometimes produced.
Uses in the Garden
American Boxwood is usually seen in gardens clipped into hedges of different heights, or as trimmed specimens, shaped into balls and cones, both round and pyramidal. It can also be trimmed into more elaborate shapes, such as spirals, and a wide variety of forms – the gardener’s imagination is the only limit. Hedges can be less than 12 inches tall, and up to 10 feet tall. American Boxwood is best for hedges in the 1 to 4-foot range, as very short ones need a lot of trimming, and the English Boxwood is a better choice for them. It takes a number of years to reach taller heights over 3 or 4 feet, so that may not be practical for some gardeners.
American Boxwood is also excellent for more informal gardens too, where it can be grown with little or no trimming. It will grow into a broad mounding plant that is perfect for filling corners, and for giving bulk to beds of medium-sized shrubs. Older untrimmed plants have a lot of character, and these untrimmed bushes should be used much more. A light trimming every few years will keep the plants dense and neat, without changing their natural habits of growth very much. It can also be used in Asian-style gardens, for the technique called ‘cloud-pruning’ or Niwaki (庭木). This method creates plants in abstract shapes and forms. Although not a traditional plant for this purpose in Japan, boxwood is easy to train into many unique forms, based on clouds, water, or other organic shapes.
Some people find the smell of boxwood unpleasant, both in the foliage and the flowers. Others do not notice it or find it perfectly acceptable. If you are uncertain, visit a garden or public park with boxwood, and check out your reaction! It will probably be fine.
Some Selected Varieties of American Boxwood
‘Dee Runk’ – a narrow pyramid, 10 to 12 feet tall and 2 to 3 feet wide at the base. Slow-growing, and so suitable for containers.
‘Graham Blandy’ – the narrowest of all, reaching up to 15 feet, but staying just a foot or so wide. Needs permanent staking in areas where snow and high winds can occur.
Golden Boxwood (‘Aureo-variegata’) – a beautiful form with pale yellow edges on the leaves, growing 6 to 8 feet tall and 3 to 4 feet wide. Lovely for trimmed shapes, striking hedges, or allowed to grow naturally.
Green Tower® (‘Monrue’) – a very fast-growing and slender variety, reaching 8 to 10 feet tall, but staying only 1 or 2 feet wide. Excellent for hedges.
North Star® (‘Katerburg’) – a dense, round ball to less than 3 feet. Needs very little clipping to keep its form.
Cultivation of American Boxwood
Besides the ease of trimming, American Boxwood is often used in gardens because it is easy to grow, and plants tolerate a wide range of conditions. Even so, it is worth considering where you want to grow it, to be sure it is suitable.
American Boxwood grows in zones 5 to 9. However, it is easiest to grow, and thrives best, in zones 6 to 8. For zone 9, we need to consider if this is the mild, damp north-east, where boxwood grows well, or the hot and humid south-east, where boxwood may suffer. If you live in the South, then varieties of Japanese Little-leaf Boxwood (Buxus microphylla var. japonica) may grow better.
In zone 5, the leaves of some varieties of American Boxwood may turn brown in winter, and the tips of young branches may die. Choose varieties with exceptional winter hardiness, such as North Star®, which stays green all through zone 5, or Green Tower® for a taller, slender hedge that stays green (this variety is also very fast growing, up to 15 inches a year). In colder parts of zone 5, and into zone 4 too, forms of the Korean Boxwood (Buxus sinica var. insularis), or hybrids, are often more reliable.
For growing boxwoods in planters and containers, you need to be two zones warmer than the hardiness rating of the variety, if the containers are outdoors, above ground, through winter. This means that plants hardy in zone 5 can be grown in pots outdoors all year round in zone 7 or warmer. In colder zones plants should be tipped out of their pots and planted in the ground in late October, and then re-potted in early April.
American Boxwood grows best in full sun in colder zones, and in more shade in warmer zones, although it will grow well in sun or partial shade everywhere. Partial shade is 4 to 6 hours of direct sunlight a day, and for boxwood that is best in the mornings, especially during summer. In warmer zones, with stronger sunlight, full shade is also suitable, especially beneath open trees. Although tolerant of shade, the growth of your boxwoods will be more open, and leaf color may be lighter, when grown in a lot of shade. The shade on the north side of buildings, fences or walls, or beneath open, deciduous trees is usually not a problem, but deep shade beneath dense evergreens is usually not suitable.
American Boxwood grows well in a wide range of soils, from sandy soils to clay. It grows well in alkaline soils too, which are like its original natural habitat. If plenty of rich organic material, like garden compost, manures, or even rotted leaves, are added to the soil when preparing the planting area, most soils are perfectly suitable. The only requirement is for good drainage, so soils that are often flooded, or always very wet, are not suitable, as root diseases soon develop.
When newly planted, American Boxwood should be watered regularly, at least once a week. After a season or two they will be more drought resistant, but the best growth is always found in plants that are not water-stressed for long periods.
Pest and Diseases
There are a number of pests and diseases of boxwood, too numerous to go into detail with here. If plants are grown in well-drained, fertile soil, and trimmed regularly, most problems will never be encountered, but if the leaves begin to yellow, or show blotches, this can indicate problems. Some can be serious, so don’t ignore symptoms, and investigate further to find solutions.
Like all trimmed plants, American Boxwood should be fertilized regularly, especially when grown in containers. In pots liquid fertilizers are most effective, while established outdoor plants can be fed with granular materials. Both chemical and organic fertilizers give good results. Look for blends designed for evergreen hedges, with a high amount of nitrogen. Do not fertilize too late in the year, especially in colder zones.
Trimming and pruning
Regular trimming will produce the densest and most beautiful growth on trimmed plants. Start trimming when plants are young and grow them steadily into their final form. Always keep the base of plants a little wider than the top, especially with taller hedges – this prevents the lower parts from dying. The first trim of the year should be in early spring, or if plants were trimmed in fall, wait until the first new growth has ripened and matured a little before trimming. You can trim as often as you want, but avoid hot, dry periods, and don’t trim after early fall, except in the warmest zones.
American Boxwood is a great plant-choice for gardening in moderate zones, and with its many varieties it offers a wide range of forms, from rounded to upright. As long as gardeners like trimmed plants, there will be a place for this plant in many gardens.