Common boxwood

Identification and origin

Buxus sempervirens belongs to the family Buxaceae. Its native range covers western and southern Europe, from Great Britain to the Iberian Peninsula, Italy, the Balkans, and Greece, as well as North Africa from Morocco to Libya, Türkiye, the Caucasus, and Iran. It has been grown in gardens since Roman times.

It is a dense, rounded evergreen shrub or small tree, branching from the base. It grows slowly: left alone it can reach 5–19.5 ft tall, but pruning keeps it much lower. Young stems are square in cross-section. The opposite, elliptic to oblong leaves are 0–2 in long; glossy dark green above and yellowish green below, they stay on the plant for about three years and can take on an orange or bronze cast in winter.

In spring it bears small, fragrant, creamy yellow flowers without petals, rich in pollen and popular with bees, followed by round capsules about 0 in across. The epithet sempervirens means “always green.”

Common cultivars: ‘Suffruticosa’, a dwarf, dense, very slow form known as English boxwood and used for parterre edging; ‘Arborescens’, which grows into a small tree; ‘Elegantissima’ and ‘Variegata’, edged in creamy white; ‘Dee Runk’ and ‘Fastigiata’, narrow and conical; ‘Vardar Valley’, low and bluish.

Light

Boxwood grows in sun or shade and even tolerates the deep shade beneath large trees. Morning sun with afternoon shade is ideal. In full sun the soil must stay moist or the foliage scorches, and heavily exposed plants suffer more cold damage. Shelter it from wind and strong winter sun, which dry out the foliage and turn it bronze.

Watering

In the ground, an established boxwood usually needs no watering except during long dry spells; then water deeply so the soil is moistened well down. Young and newly planted shrubs should stay in soil that is moist but never waterlogged.

In a container, boxwood has fewer reserves: check the mix all year round, even in winter, and water as soon as the surface dries. Before a hard cold snap, a thorough watering limits foliage desiccation, since the leaves keep losing water through the winter.

Its shallow roots grow in the top 15 in of soil and spread beyond the canopy. An organic mulch 2–3 in deep keeps them cool, conserves moisture, and lowers the risk of disease; remove the old mulch before adding a fresh layer each year.

Potting mix

Boxwood adapts to clay, loam, sand, or humus-rich soils as long as they drain well: never plant it under a downspout or in a low, wet spot. It prefers a neutral to slightly alkaline pH, so it pairs poorly with acid-loving plants such as azaleas or camellias. Do not plant it too deep: the top of the root ball should sit slightly above the soil, because deep planting weakens it.

In fertile soil it needs no fertilizer; feed only when a need has been confirmed, in early spring, never in summer or fall, as excess fertilizer browns the leaves. In containers, apply an organic liquid fertilizer in summer.

Temperature

Common boxwood is hardy and grown in USDA zones 5a to 8b; it tolerates heat less well than littleleaf boxwood (Buxus microphylla). Its young shoots are vulnerable to late frosts, which turn them pale brown and papery, and winter cold can yellow leaf tips and margins.

Repotting

Plant preferably in fall or spring. For a hedge, space plants 12–16 in apart; compact forms such as ‘Suffruticosa’ go 4–6 in apart. A dense edging fills in within three to five years.

In a container, choose one at least 18 in across and a loam-based mix. Each spring, top-dress established plants: scrape off the top 2 in of mix and replace it with fresh mix plus a little slow-release fertilizer.

Pruning

On young plants, cut stems back by up to one-third in late spring to encourage branching. Mature plants are best trimmed in late summer, once the new shoots have hardened. Trimming too early triggers soft growth that is vulnerable to scorch, frost, and disease; trimming too late leaves regrowth with no time to harden before frost.

Also thin the interior every year, whenever it is not freezing, by removing some branches at the outer edge to let in air and light. This is essential for ‘Suffruticosa’, whose center tends to go bare. An old, neglected boxwood tolerates hard pruning in late spring, down to 6–12 in from the ground; for a major renovation, work in two years instead, one side at a time.

Propagation

Cuttings root very easily. In early to midsummer, take semi-ripe cuttings when the new growth is starting to firm up. In a heated propagator they root in about eight weeks; in a cold frame, allow about eight months. They also root directly in the ground if the soil is moist and shaded. Pinch the tips once they start growing. In fall, line them out in a sheltered spot 12–18 in apart: they will be ready for their final position after three or four years.

Sow seed in fall or early spring in peat-free seed-starting mix in a cold frame, never letting it dry out. It takes four to five years before the young plants are big enough for the garden.

Common problems

• Boxwood blight: a serious fungal disease; common boxwood is the least resistant species, and ‘Suffruticosa’ is very susceptible.
• Box tree moth: its caterpillars can badly disfigure hedges and topiary.
• Boxwood psyllid, mite, leafminer, and scale insects: check the foliage regularly; ‘Vardar Valley’ resists leafminer.
• Leaf spots and twig dieback: encouraged by foliage that is too dense and poorly ventilated.
• Root rot, overall yellowing: waterlogged soil, especially heavy clay.
• Bronze or orange foliage: weather stress, summer drought, or roots damaged by standing water in winter.

The same symptom can have several causes: weigh exposure, drainage, season, and a close look at the leaves before treating.

Toxicity

Toxic to dogs, cats, and horses, and to people. The leaves contain steroidal alkaloids. In dogs and cats, eating them causes vomiting and diarrhea; in horses, colic, diarrhea, seizures, and respiratory failure. In people, ingestion can cause nausea, vomiting, diarrhea, dizziness, convulsions, and respiratory failure. The sap can irritate the skin, so wear gloves for major pruning. If any part is swallowed, contact a veterinarian or a poison control center.