Boxwood For Ornamental Gardens

Boxwood (Buxus) have been a popular choice for ornamental gardeners, world wide, for 1000’s of years. These versatile evergreen shrubs have graced the homes of royalty, large public gardens, commercial properties and home gardens of all styles and sizes. They are relished for their slow growth, compact size, and ability to handle tight sheering, making them popular choices for hedges and topiary. Read on to learn about their history, how to care for boxwood, some common pests and diseases and popular varieties and cultivars.

The formal boxwood and yew topiary/hedges at Niagara Falls Canada.
The boxwood hedges and topiary at the Toronto botanical gardens.

History 

Fossilized remains of buxus plants date back to over 22 million years ago. In 4000 B.C. Egyptians used clipped box hedges in their gardens, as did Emperor Augustus during his reign of the Roman empire in 27 BC-14 AD. Since those times there has been a rich documented history of the use of buxus in the landscape. Boxwood was introduced to North America from Europe in the mid-1600’s, where it continues to be utilized in both traditional and contemporary landscapes.

Boxus Wood

The word buxus is Latin for the word box and is thought to have been named for its common use in the making of highly decorative boxes. Owing to its very fine texture and exceptional hardness, buxus wood, is particularly well suited to carving. It is one of the few woods that are denser than water. Boxwood has been used to make recorders, combs, printing blocks and handles for tools. Today boxwood is commonly used to make highly detailed chess pieces and parts for musical instruments.

Boxwood hedging encircles this Juniper cloud tree.
Curving Boxwood hedge.

Cultural Practices

Light requirements: Boxwood will grow in full sun but many prefer part shade. The species Buxus Microphylla the hybrids from the Green Series are more sun tolerant.)

Soil pH: Boxwood prefer a soil pH between 6.5 and 7.

Moisture: Moist well drained soil is preferred, but they are typically quite drought tolerant once well established. Boxwood hate wet feet and are highly susceptible to root rot when grown in standing water.

Propagation: Stem cuttings are the most common technique but layering is also an option. When selecting stems to cut choose smaller 1-year old branches, they are said to have a higher concentration of growth hormones. Non hybrids can be grown from seed, to do this scarify the seeds and plant them at a depth of about 1”. Germination will take anywhere from 30 to 190 days. 

Mulching: Boxwoods are shallow rooters and benefit from a shallow layer of mulch to protect the roots. Deep mulching should be avoided as it may encourage roots to grow above the soil surface putting them at high risk of damage when dried out. 

Salt spray: Most boxwood are very sensitive to the salt spray from roadways, and deicing salts from side walks and driveways; plant them far enough away from these areas to avoid injury.

Poisonous leaves: The leaves of boxwood contain steroidal alkaloids making them mildly toxic to both humans and animals.

Pruning: Boxwood can take repeated close shearing making them a popular choice for topiary, bonsai, and formally clipped hedges and shrubs. Species and cultivars (such as Buxus sempervirens) with a dense growth habit benefit from thinning to open up their centers to better air and light circulation. This encourages growth of leaves on the interior and may help to reduce disease.

Boxwood clould tree.

Pests and Diseases of Boxwood

Boxwood blight: a fungal disease causing rapid and severe defoliation. Caused by the pathogen,  Cylindrocladium buxicola. Symptoms first appear as leaf spots that are light to dark brown, with or without a dark border, as well as stem lesions or cankers. After infection has taken place white spore masses develop on the undersides of leaves. Leaves then develop black, cloudy spots that lack a distinctive edge. These spots often enlarge to encompass the whole leaf, and then the leaf usually drops from the plant. The disease is systemic and the entire plant is usually affected. Wounding is not required. According to the American Boxwood Society the following 10 boxwood cultivars/var. are least susceptible to boxwood blight: “Green Beauty, Northern Emerald, Wedding Ring, Wintergreen, Golden Dream, Winter Gem, Nana, Franklin’s Gem, Wee Willie, and Richard. “

Volutella blight: a less serious fungal disease caused by the fungus Pseudonectria buxi, formerly called volutella buxi. Symptoms include salmon coloured cushions on lower leaf surfaces and some stems, followed by yellowing and then leaf and stem death. Black streaks are sometimes visible on petioles and stems. Affected branches slowly dieback and the dead leaves tend to stay on the plant for months, rather than dropping. Unlike boxwood blight, wounding is required for this infection to take place. Pseudonectria buxi requires 18 hours of wet conditions in order to germinate.

Spider mites: leaves of injured plants appear stippled.

Phytophthora root rot: Caused by the fungi, Phytophthora. Plant boxwood in well drained soil to help prevent this disease. Buxus sempervirens ‘Suffruticosa’ and Buxus sempervirens ‘Arborescens’ are most susceptible.

Winter Bronzing: leaves turn a bronze colour as the result of exposure to cold, dry winter winds. Plant boxwood in a sheltered spot or place physical barriers (about 18” away from the plant) on the windward side to protect them.

Nematodes: are microscopic, worm-like organisms that feed on the roots. Plants appear to be in decline and appear smaller than normal.

Boxwood Leaf Miner: damage appears as blotch mines between the upper and lower leaf surfaces. American boxwood tends to be the most susceptible.

Boxwood decline: older English boxwoods, particularly those grown in full sun and drier soils, show a slow progressive decline.

Boxwood Psyllid: Feeding of this insect causes the outer leaves to curl and form a cup which encloses the nymphs. 

Box Tree Moth: is a serious, new pest to Canada and the USA. The larvae of this moth can cause extensive defoliation to boxwoods. The larvae are tiny green caterpillars with black heads, black spots and black stripes that run down their length. They measure between .5cm and 4cm in length, depending on which instar larval stage they are at (there are 7 instar stages). The caterpillars are difficult to spot, as they are small, often located on the underside of leaves and blend well into the foliage. They typically begin feeding on the inside of the shrub working their way out. You will likely spot their damage (chewed and defoliated leaves) and silk webbing covered in frass, shed skins and head capsules before you spot them. Feeding damage initially appears on one side of the leaf (usually the bottom) being eaten while the other side remains intact. This type of damage is called ‘window paning’. This is followed by desiccation and browning. As the caterpillar grows entire leaves, except for the mid-rib, are consumed. The caterpillar also feeds on the stems causing girdling and branch dieback.

3 Boxwood clipped into cone shapes.
Boxwood hedge encircling an ornamental fountain.

Popular Selections for North American Gardens

According to the American Boxwood Society there are currently148 cultivars of boxwood which are currently available commercially. Many of these of these are better suited to warmer climates but there are a few species and several notable varieties and cultivars that are suitable for temperate climates such as Canada.

1. American Boxwood (Buxus semperviren)

Often referred to as common boxwood. It is a slow growing broadly rounded, dark green, multi-branched shrub, that can reach up to 15 to 20 feet tall at maturity. This species is not as heat tolerant as B. microphylla but has good insect pest and disease resistance. Has a tendency to bronze in the winter. Native to western and southern Europe, western Asia, and northern Africa. It is one of the parent plants for the popular hybrids Green Series (Buxus sinica var. insularis × B. sempervirens).

Cultivars

  1. ‘Suffruticosa’: Often referred to as English Boxwood. This species is native to Europe, North Africa and Western Asia. Most notable characteristics of this dwarf cultivar include light green foliage colour, a tight growth habit and slow growth rate (averaging only 1”to 2″ of growth per year) with a mature height of typically 3’ to 5′; but they can be very long lived shrubs and grow larger as a result. Hardy in zones 6-8. English boxwoods have a tendency to bronze in the winter and mature shrubs are susceptible to boxwood decline, especially when grown in full sun.
  2. ‘Arbvorescens’: Often referred to as Tree Boxwood. This is a faster growing cultivar with a looser growth habit. Average height 8’-10’; oval in shape; leaves pointed.
  3. ‘Vardar Valley’: grows to be about 2′ tall by 3′ wide. The new growth in the spring is powdery blue which matures to a deep green. It holds the deep green color through the winter. It grows about 1″-3″ per year. Hardy zones 5-8.
  4. ‘Fastigiata’: A narrowly columnar boxwood that can be pruned into a tight coned. Grows to about 6′ tall and 2′ wide. The foliage is rich green with a hint of blue. Grows about 3″-6″ per year. Hardiness Zone: 6-8
  5. ‘Elegantissima’: has unique green leaves with white borders. Grows to about 2′ tall by 3′ wide. It grows about 1″ – 2″ per year. Hardiness Zone:6-8.
  6. Dee Runk’: A columnar boxwood that can be pruned into a tight cone. Grows to about 7′ tall by 3′ wide. Grows about 3″-6″ per year. Hardiness Zone: 6-8.
  7. ‘Vardar Valley’: has dense, compact, growth habit. Grows to about 2-3′ tall. Grows about 1″-3″per year.
  8. ‘Calgary‘: is a dense globe-shape shrub that is extremely cold tolerant. Grows 2′-3’. Growing Zones 3-9.

2. Japanese Boxwood (Buxus microphylla)

Buxus microphylla is often referred to as little-leaf boxwood. It originated in the far East centuries ago.

Cultivars:

  • ‘Little Missy’: a compact globular shaped shrub with glossy, dark green leaves. It grows to about 2′. It is very cold hardy and sun tolerant. Hardiness Zone: 5-8.  Ranked high in resistance to Boxwood Blight.
  • Northern Emerald‘: Dark green foliage. Grows to 3′ high by 4’ wide. Hardiness zone: 5-8. Similar to Wintergreen and Winter Gem. Good resistance to boxwood blight.
var. japonica

Buxus microphylla var. japonica is native to Japan and Taiwan this species is more tolerant of heat and drought, but like sempervirens it has a tendency to bronze in the winter. Growth habit is compact and rounded averaging 3′-5’ in height but can get as tall as 6′. Hardiness zone: 6 to 9.

Cultivars:

  • ‘Green Beauty’: Forms a globular shape growing about 3′. Grows about 2″-4″ per year. Hardiness Zone: 6-8. Prone to bronzing in the winter. Good resistance to boxwood blight.
  • ‘Borderline’: This variegated cultivar has dark green leaves with yellow margins.
  • ‘John Baldwin’: forms a conical shape growing 4′ tall by 3′ wide. Blue-green foliage. Good resistance to boxwood blight. Hardiness Zone: 6-8
  • Morris Midget’: is a faster growing boxwood growing up to 12″ per year, It has an open upright growth habit that matures to about 6-8′ tall by 16′ wide. Leaves are about 1″ long, rounded and glossy. Hardiness zone: 5-9
  • ‘Morris Dwarf’: a very compact shrub growing to about 1′. It is excellent for edging formal beds or in parterre gardens. It’s a slow growth rate of only 1/2″-1″per year makes it very low maintenance.
  • ‘Golden Dream’: A dense, rounded, and compact shrub with rich green variegated foliage accented by bright gold margins. Grows to 3′. Grows about 1″ to 3″ per year. Hardiness Zone:6-8. Good resistance to boxwood blight.
  • ‘Jim Stauffer’: Forms and oval shaped shrub with dark green foliage, glossy foliage that holds it’s colour well over winter. Grows to about 3′ tall and 4′ wide. Grows about 2.5″-5″ per year. Hardiness Zone: 5-8
  • Winter Beauty‘: Forms a globular shape growing to about 3’. Growing Zones 4-8. Foliage is glossy and medium-green in colour but in the winter the leaves turn a lovely orange to coppery color.
  • ‘Wee Willie’: Compact, dense, rounded shrub with dark green leaves that holds it’s colour well in the winter. Grows to 2′. Hardiness zone: 5-9. Good resistance to boxwood blight.
3. Korean Boxwood (Buxus sinca var. insularis)

Formerly Buxus microphylla var. koreana and Buxus microphylla subsp. sinica. Native to China and Taiwan. It is known for being more cold tolerant. This species forms a dense, compact shrub. Leaves may bronze in the winter. It is one of the parent plants for the popular hybrids Green Series (Buxus sinica var. insularis × B. sempervirens.)

Cultivars 

  • ‘Nana’: a light green, compact shrub that grows to about 2′ tall by 3′ wide. Grows 1″ to 3″ per year. Hardiness zone: 5-8. Good resistance to boxwood blight.
  • ‘Wintergreen’: Formerly called Buxus microphylla var. koreana ‘Wintergreen’. Globular shape that grows to about 4′. Grows about 4-6″ per year. The oval shaped leaves are glossy and dark green. This cultivar is less likely to bronze in winter. Hardiness Zone : 6-8. Good resistance to boxwood blight.
  • ‘Winter Gem’: also known as Buxus microphylla var. japonica ‘Winter Gem’ or Buxus microphylla var. koreana ‘Winter Gem.’ Globular shape about 3′ in size. It has rich green foliage that is prone to bronzing in the winter. Hardiness Zone: 6-8. Good resistance to boxwood blight.
  • ‘Eseles’: Trade name: Wedding Ring® a variegated globular shaped boxwood. Grows 2′ to 3′. Hardiness zone 5-9. Good resistance to boxwood blight.
  • ‘Franklin’s Gem‘: Dense and mounding shrub that grows to 2’. tall by 3′ wide. It has bright green foliage that turns an attractive olive-green during winter months. Hardiness zone: 4-9. Good resistance to boxwood blight.
4. Hybrids

Chicagoland Green ® (Buxus x ‘Glencoe’): Oval shaped shrub grows 3′ to 4′ ft. tall and wide. Has glossy green foliage that holds it’s colour well in winter. Hardiness zone 4-9.

The Green Series

The green series introduced in Ontario by Sheridan Nurseries are a cross between Buxus sinica var. insularis × B. sempervirens. These boxwoods are more cold hardy with less winter bronzing and tolerate full sun better than many varieties. Their growth habit is compact and fairly dense and tend to require little pruning, although they can be easily sheared to desired shapes.

  • Green Velvet: has bright green foliage that turns an attractive olive-green colour during the winter months. It growth habit is somewhat spherical. Grows to about 2′ tall by 3′ wide. Hardiness Zone: 5-8
  • Green Mountain: has a conical shape. and bright green foliage. Grows to about 4′ tall by 3′ wide. Prone to winter bronzing. Hardiness Zone: 5-8.
  • Green Gem: Has a spherical growth habit. Grow to about 2′ tall by 2′ wide. Prone to winter bronzing. Hardiness Zone:4-8
  • Green Mound Has a spherical growth habit with  emerald green foliage. Grows to about 2′ tall by 2′ wide. Grows about 2″-3″ per year. Prone to winter bronzing. Hardiness Zone: 4-8
A row of clipped boxwood balls an alternative to a hedge.
3 Green Velvet boxwood Boxwood balls accent the front of this garden bed.

Summary

Whether you are looking for an evergreen to naturalize, a small tidy tree or a highly ornate shrub, boxwood has a species or a cultivar to suit almost any landscaping need. These popular shrubs are steeped in tradition and even though they have some potential insect pests and disease problems they are still considered an easy to grow shrub.

Photo credit: all photos have been taken by and are the property of the author.

Resources:
Books

  •  Diseases and Pests of Ornamental Plants (fifth edition); Pascal P. Pirone; The New York Botanical Garden 1978 
  • Lois Hole’s Favorite trees & Shrubs; by Lois Hole with Jill Fallis; 1997 Lois Hole and Lone Pine Publishing
  • Ever Green Shrubs; Alexandria, Va.; Time Life Books 1989

Articles

  •  Growing Boxwoods in the Landscape; Erv Evans, extension Associate; Richard E. Bir, Extension Specialist; Stephen Bambara, Extension Entomology Specialist; Department of horticulture Science, North Carolina Cooperative Extension Service (revised 2/99)
  • Major Diseases of Boxwood; Mary Ann Hansen, Extension Plant Pathologist, department of plant pathology, Physiology and Weed Science, Virginia Cooperative Extension, Virginia tech, and Virginia State University, May 2009
  • Volutella blight of boxwood; Fang (Amy) Shi and Tom Hsiang; School of Environmental Sciences, University of Guelph

Websites

https://www.boxtrees.com/buxus.html#Buxus%20balearica

https://www.saundersbrothers.com/Plant-Category/Boxwood

https://boxwoodsociety.org/

https://www.boxtrees.com/buxus.html#Buxus%20microphylla%20%60Golden%20Triumph%60

https://www.missouribotanicalgarden.org/plantfinder/plantfinderdetails.aspx?kempercode=q130

https://plants.ces.ncsu.edu/plants/buxus-microphylla-var-japonica/

https://plants.ces.ncsu.edu/plants/buxus-sinica/

https://www.monrovia.com/chicagoland-green-boxwood.html

https://plants.ces.ncsu.edu/plants/buxus-sempervirens/#:~:text=Description%20American%20boxwood%2C%20or%20common%20box%2C%20is%20a,Africa.%20The%20species-specific%20epithet%20sempervirens%20means%20always%20green.

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