Boxwoods

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Boxwoods for

Pennsylvania

Landscapes

College of Agricultutal SciencesAgricultural Research and Cooperative Extension

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WEach species contributes unique

characteristics, including size, color,

insect resistance, and oliage. Common

boxwoodis a wide-spreading species

with very dense, evergreen oliage

and cold tolerance to about -50F. Te

leaves are dark green above and yellow-

green below, reaching 1/2" to 1 1/

2" in

length, and are oblong to oval in shape.Japanese boxwood is a low-growing,

compact, heat-tolerant shrub with

bright green leaves that are elliptical

to lance-shaped, and reach 1/4

to 1" in

length. Korean boxwood is a loose,

open-growing shrub that is very hardy,

although the oliage may turn yellow

to brown in the winter. In the nursery

and landscape trade today, numerous

varieties and hybrids among these spe-

cies have been created and marketed ortheir unique characteristics, including

round, dwar, and columnar orms,

winter hardiness, and variegated oliage

Among the boxwoods on the market,

the ollowing list represents cultivars

o various orms and characteristics

that may be useul in the many dier-

ent environments and landscapes o

Pennsylvania.

inter in many parts o Pennsylvania

provides a stark, leaess, snow-covered

scene among the deciduous hardwoods,

intermixed with dark green patches

o hemlock and other needle-leaed

evergreens. Many homeowners look

to enhance this beautiul scene with

broadlea evergreens in their landscape.

Tere are a number o broadlea ever-green shrubs to choose rom that are

suitable or the Pennsylvania landscape,

including pieris, mountain laurel, leuco-

thoe, mahonia, pyracantha, leatherlea

viburnum, rhododendron, holly, and

boxwood. Most o these plants provide

a rounded and spreading habit. For

ormal gardens, hedges, or sites where a

specic plant orm is desired, Japanese

holly and boxwood are the most com-

mon choices.

Boxwoods (Buxus) are native to Europe,

the Mediterranean, the West Indies,

Asia, and Central America. Te genus

Buxusconsists o thirty species, o

which there are approximately 115

dierent cultivars and species commer-

cially available. A cultivar is a plant o

a particular species, such as Elegantis-

sima, a common boxwood that shows

a unique characteristic o variegatedlea color that can only be reproduced

through vegetative propagation. Te

most commonly available species are B.

sempervirens(common boxwood) and

B. microphylla (Japanese or Littlelea

boxwood) and their cultivars. A third

less, common species, Korean boxwood

(B. sinica var. insularis),is also available,

and has provided a source or increased

cold hardiness.

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Botanical Name Cultivar Name Zone Height Width Adaptation and Remarks

Upright Forms Use: Specimen, doorway, or corner accent

B. sempervirens Dee Runk 6 1012' at 25 yrs 22.5' Conical grower, distinctively upright when pruned

to central leader. Perorms well in heavy soils

compared to other uprights. One o the best

upright cultivars.

B. sempervirens Fastigiata 6 12' at 40 yrs 5' Moderately ast conical with minimal bronzing in

winter. One o the richest green colors amonguprights. Second in tolerance to heavy, poorly

drained soils.

B. sempervirens Graham Blandy 6 1012' at 25 yrs 11.5' Columnar with new, succulent growth bending out

and downward. Less eective than above two.

Prone to root-rot problems in heavy soils.

Very Dwarf Use: Edging, specimen, bonsai, or dwarf garden

B. microphylla Grace 56 11.5' at 25 yrs 33.5' Annual growth o " to " in height by 1" to

Hendrick 2" in width. Rich green oliage. Excellent dark

Phillips color when placed in shade rather than ull sun.

B. microphylla var. Morris Midget 56 18" at 40 yrs 3' One o the most compact mounded cultivars, with

japonica 1" growth each year. A smoother appearance

than its sister Morris Dwar.

B. microphylla Green Pillow 5 30" at 30 yrs 40" Low-mounding and slow-growing. Holds new,

light-green oliage longer than others. Foliage may

be rosted in all.

B. microphylla var. Morris Dwar 56 3' at 40 yrs 4.5' A compact plant originating rom an open-

japonica pollinated seedling at the Morris Arboretum in Pa.

The tuted bush outline is the result o clusters o

23" brittle shoots. Shoot reversions are possible,

requiring monitoring and pruning.

Slightly Dwarf to Medium Size Use: Edging, specimen, and formal gardens

B. sinica var. Nana 6 18" at 17 yrs 3' A low, broad-spreading grower. Commonly called

insularis dwar Korean. May require annual tipping o the

branches to improve their rigidity. Site sensitive,

this plant with its rich green, oliage is most

attractive in shaded sites. Spring oers a crisp,

lime-green color due to new growth.

B. sempervirens Jensen 6 12" 6" A newcomer and relative unknown rom southeast

Pa., this plant produces beautiul, bluish-green

oliage and resembles Suruticosa in oliage

shape, and growth habit. Little is known about this

plant's maximum height.

B. sinica var. Justin 6 22.5' at 25 yrs 3.5' A seedling originating rom Williamsburg, Va. and

insularis Brouwers resembling English boxwood. Producing narrow,

dark-green oliage on a dwar-mounding plant.

This cultivar appears more tolerant to sun and

heavy soils than English boxwood. Richer oliage

will be ound i it is grown in some shade. The

leaves are pointed and produce delightully sot

spring oliage. This cultivar needs little pruning and

can be allowed to grow naturally. Sensitive to

exposed sites.

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Medium Size Use: Christmas decorations, topiary, hedges, and specimen

B. sinica var.insularis Green Mountain 4 5' at 20 yrs 3' The astest growing o the Sheridan Nurseries

B. sempervirens (Ontario, Canada) releases, this plant can be a

striking conical or columnar orm with pruning.

B. sinica var.insularis Chicagoland 4 3-4' at 15 yrs 5' A patented cultivar rom the Chicagoland Grows

B. sempervirens GreenTM Introduction Program o the Chicago Botanic

Glencoe Garden, Glencoe was introduced because o itscold hardiness, uniorm oval-rounded habit,

attractive green winter color, and ease o propaga-

tion. Field-grown plants exhibited no measurable

damage ater exposure to record-low tempera-

tures o 27 degrees F during 1993-1994.

B. sempervirens Suruticosa 6 4' at 50 yrs 5' A colonial and modern avorite, ormal and dense

(English) in its growth habit, orming a rounded cloud and

growing 1-2" each year. Preers a soil pH above 6,

protection rom southern and western exposure,

dappled shade, and protection. This cultivar is

susceptible to boxwood decline. One by one,

large branches turn rom green to yellow and

slowly the entire plant dies due to a root-rot

pathogen. Full-sun plantings are most susceptible

although crowded centers with no air circulation

may contribute to its decline.

B. sinica var.insularis Wintergreen 5 4' at 15 yrs 6' Considered one o the hardiest cultivars, with a

broad, vase-shaped habit. There are many

dierent plants under this cultivar name, some

with a larger sempervirens-type lea and others in

the Midwest with the characteristic small, sinica

lea shape. Wintergreen is a great Japanese holly

substitute. It requires some shearing to maintain

its light shape. A very ast grower and difcult to

maintain as a ormal plant. Usually maintains

good color through winter. A heavy seed producer

B. sempervirens Vardar Valley 4-5 4' at 30 yrs 10' A willowy spreader, this cultivar remains open and

very hardy. Originating rom Macedonia, this

plants bluish-green oliage in springtime adds

distinctive class to the landscape, giving way to a

rich green later in the season.

B. microphylla Green Beauty 6 3-7' at 15 yrs 34' An excellent dark, winter color, and adaptability to

var. japonica sunny and exposed sites, makes this cultivar a

possible substitute or English boxwood. Clipping

annually to remove leggy shoots will help to

maintain its spherical shape. This cultivar appears

a bit more brittle than most.

B. sinica var. Green Ice 4 3' 3' Patented by Conard-Pyle, this plant is considered

insularis super hardy, maintaining a deep-green winter

sempervirens color. The new spring growth is blue-green, which

turns a glossy, deep green in the summer, resem-

bling its B. sempervirens parentage. Little is

known about the maximum size o this plant.

B. microphylla Jims Tru 5 3' at 15 yrs 4' A Pa. introduction by Jim Stauer, this var.

Spreader japonica cultivar appears extremely winter hardy

and adaptable. Similar to Green Beauty, but has

a more spreading habit and is hardier.

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Large Cultivars Use: Christmas decorations, topiary, hedges, and specimen

B. sempervirens Common or 5 12' at 50 yrs 9' A colonial avorite, oten called tree boxwood, this

American plant is a benchmark standard or boxwood

upright or pyramidal orm, this plant is a ast

grower that will tolerate more open sites than

English boxwood. Susceptible to root-rot dis-

eases, this plant needs a well-drained soil. To

prevent light bronzing o the oliage in winter, plantin a protected site under trees and away rom

southwestern exposure.

B. sempervirens Elegantissima 6 12' at 40 yrs 6' Outstanding and distinctive boxwood with creamy

white edges around each lea, oering a contrast

in the landscape. A moderate grower that is cold-

sensitive. Some shade enhances the contrasting

oliage. Growing under pine trees or other shade

structures may also provide the type o winter

protection this cultivar requires.

B. sempervirens Inglis 5 7' at 20 yrs 6' First recognized in Michigan, this plant appears to

grow more slowly than common sempervirens and

appears more controllable, yet it can fll a space

quickly. Susceptible to root rot in heavy soils. In

early tests, it appears to be coming through

winters with a rich color and good, tight orm.

Boxwood Culture

Most boxwood cultivars require

protection, mainly to avoid mid- and

late-aternoon sun damage during both

the winter and the hot days o sum-mer. Winter sun damages boxwood by

discoloring the oliage almost imme-

diately, and extended damage weakens

the plant, oten resulting in death.

Late- aternoon winter sun creates two

problems or boxwoods: the bronz-

ing or discoloration o oliage, and

the overheating o oliage and stems,

ollowed by reezing o the tissues ater

sunset when temperatures drop rap-

idly. Tis rapid temperature change inactive and warm tissue can burn tender

lea tissue and cause rost-cracking o

exposed stems and branches. Tought-

ully locating the plants in protected

sites, overhead shading rom canopy

shade trees, and the use o articial

barriers such as snow ences, will relieve

the drastic day and night temperature

uctuations, thus reducing the likeli-

hood or overheating and super-cooling

o the plants tissues.

Locating plants in the landscape

requires an understanding o your

individual landscape conditions. When

placing boxwoods in a landscape, the

north side o a structure or landscape

planting is preerred, ollowed by the

east side, then the south side, and

lastly the west side. Te north side o a

building, structure, or taller landscape

planting prevents direct sun light rom

striking the plants. Planting boxwoods

on the east, south, and west sides o a

structure, building, or taller landscape

planting can result in direct exposure to

sunlight in the morning, during the day,

or in the evening. Where a northern

location is not possible, careul selection

o tolerant cultivars and temporary shel-

ters are alternative approaches to adding

boxwoods to your landscape.

Boxwoods are sensitive to drought.

Newly planted boxwoods require

attention to watering during the rst

growing season to prevent the soil rom

drying out around the roots. Te soil

should be slightly moist below the sur-

ace all year round. As a general guide,

boxwoods should receive about 1" o

rain every ten days. Keep track o rain-

all and supplement as necessary with a

long, slow soaking rom a soaker hose

or trickle irrigation. Adequate water

should be applied to penetrate into

the top 6 to 8" o soil. Mulching will

help to conserve moisture around the

plants. Established boxwoods should be

watered in the spring and early sum-

mer i adequate rainall is not recorded.

Plants that are drought-stressed in the

spring and summer may produce an

overabundance o late summer or early

all growth i rain levels increase. Tis

new succulent growth may not harden-

o properly and may reeze during the

winter. I rainall levels remain low in

the all, soak the ground with water to

a depth o 6 to 8" prior to the ground

reezing to assure a moisture source or

the plant through the winter.

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Boxwood mite

Te boxwood mite, Eurytetranychus

buxi(Garman), is primarily a pest o

boxwood, Buxussempervirens. It is a

common and widespread species.

Tis pest overwinters in the egg stage.

One emale may lay 2535 eggs. Te

lemon-yellow eggs hatch rom late April

through early May. Eggs hatch in 6 to

10 days, and the yellowish-green larvae

start to eed on the host plant. Nymphs

are green to yellowish-brown. Adults

may live or 2 to 5 weeks. Tis species

completes one generation in 18 to 21

days, and at least eight generations are

produced each year in Pennsylvania.

Feeding injury on boxwood rst

appears as mottling, ollowed by yel-

lowing and browning near the midvein

on the lower lea surace. Small comma-

shaped spots are apparent on the upper

lea surace o inested plants. Heavily

damaged oliage becomes bronzed and

may drop prematurely. All lie stages

may be ound at one time on severely

inested plants, on both the upper and

lower lea suraces. Tis species preers

to eed on tender shoots and the upper

surace o young oliage. In warm and

dry growing seasons, this pest becomes

very abundant and may cause consider-

able damage.

Dormant horticultural oil should be

applied according to label directions,

during the overwintering egg stage.

Inested plants also can be treated with

registered miticide ormulations when

active lie stages o this pest are present.

Pests of Boxwoods

Listed below are some key arthropod

pests and diseases that cause injury to

boxwoods in Pennsylvania. Manage-

ment suggestions are also provided or

these species. Consult your current

woody ornamental pest management

guide or ormulations registered or

management o these pests.

Boxwood leafminer

Te boxwood leaminer,Monarthro-

palpus avus(Schrank), is a key pest o

Pennsylvania plantings o boxwood,

Buxusspp. It was rst reported as a

pest in the United States in 1910. It

is now ound coast to coast wherever

boxwood grows.

Te eggs are white to transparent, and

they hatch to small, whitish to lemon-

yellow, 3 mm long larvae (maggots).

Adults are small, yellow to orange-red,

2.5 mm gnat-like ies.

Tis species overwinters as larvae in

the lea blister. During the spring this

blister develops a translucent window.

Te larvae change into the restingstage (pupae). During May, the pupae

wriggle through the blister window

and protrude rom the lower lea sur-

ace. Adults emerge rom these pupal

cases during May and mate soon ater

emerging. Mated emales deposit eggs

into new oliage by thrusting a curved,

needle-like ovipositor through the

lower surace o the lea. Eggs may be

seen easily, especially on new growth,

by holding the lea up to the light.Ater laying an average o twenty-nine

eggs, the emale dies. Eggs hatch into

young larvae in about 1421 days.

Larvae continue to grow and eed in

the lea through the remainder o the

summer. One generation o this pest

occurs each year.

Te larval stage o this pest can cause

extensive damage to the oliage. Injury

to the host plant is caused by this stage

eeding between the upper-and lower

lea surace. Feeding produces a blister

on the lea that may or may not become

discolored. Heavily inested leaves may

contain several lea blisters, and the

entire lea may become pued or swol-len. Inested leaets oten drop pre-

maturely, resulting in ragged-looking

plants with occasional dead twigs. Most

varieties o boxwood are attacked by

this pest.

o manage this pest, apply registered

insecticides, according to label direc-

tions, during May.

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Boxwood psyllid

Te boxwood psyllid, Cacopsylla buxi

(Linnaeus), is a common pest o box-

wood, Buxusspp. It is not considered

as destructive as other boxwood pests.

Plants o common boxwood, B. semper-

virens, appear to be most susceptible to

this pest.

Its eggs are very small, orange, and

spindle-shaped. Nymphs have piercing-

sucking mouthparts and are covered

with a white, waxy secretion that

readily distinguishes them rom other

insects that attack boxwood. Adults are

about 3 mm long, and greenish in color.

Tis species overwinters in the egg

stage. Te eggs are laid between bud

scales o the host bush during early

summer and start hatching as soon

as buds begin to open in early spring.

Young nymphs immediately begin to

eed on plant tissue by removing uids.

Nymphs develop on newly expanding

oliage. Leaves become cupped and can

enclose several nymphs inside a pocket

o oliage. Te nymphs usually mature

into adults by early June. Ater mating,

adults deposit eggs that overwinter on

the host plant. One generation occurs

each year in Pennsylvania.

Feeding damage is very noticeable due

to the lea-cupping eect that young

nymphs produce on host plants. Lea

cupping results rom injury to tissue as

it is ormed in rapidly expanding leaves.

Occasionally, young twig growth is

aected by this species.

o eectively manage this pest, treat

inested host plants with a registered

insecticide when nymphs are present in

early May.

Decline

During boxwood decline, plants are

stunted, and dieback o middle and

upper branches occurs. Young oliage

turns gray-green or bronze and nally

straw color, while old leaves all pre-

maturely. Sunken cankers orm on the

trunk at the soil line, or on branches in

the crotches where dead leaves accumu-

late. Wood under the sunken canker is

blackened.

Decline is the result o attack by

various ungi. Nematode eeding on

roots contribute to the decline, as

does damage rom winter injury and

the stress on plants in poorly drained

sites. o manage decline, protect

plants rom winter injury and ooding

stress. Prune dead branches well below

cankered areas. Remove dead leaves

accumulated among the branches. I

the shrub is removed, do not replace

it unless the soil is rst umigated and

aerated, or treated with a nematicide

beore planting.

Leaf spot

When a boxwood has lea spot, straw-

yellow leaves are dotted with small,black, ungal-ruiting structures o the

ungusMacrophoma candollei. Only

leaves weakened by winter injury are

inected. o manage this lea spot, pro-

tect plants rom wind, sa lt spray, and

salt runo.

Leaf burn

When a boxwood has lea burn, lea

tips and margins yellow and red-

den as leaves all prematurely. Waterstress and low temperatures result in

lea burn. Tereore, protect shrubs

rom drought and drying winds in the

autumn and winter.

Nematodes

Root-eeding nematodes, including

Pratylenchus, slow growth and cause

stunting. Te leaves o nematode-

inected plants have a bronzed appear-

ance and the shrub declines. Small

roots have small, brown, dead areas

that enlarge to engul the entire root

ends. Tere are no adequate controls

once the plant is inected. I the shrub

is removed, do not replace it unless the

soil is rst umigated and aerated, or

treated with a nematicide beore plant-

ing. Fertilizing the plants will over-

come the oliar symptoms. However,

nematodes also will benet rom the

increased plant nutrition and be able to

increase their numbers. Tis, then, only

worsens the problem over time.

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Prepared by James Sellmer, assistant

proessor o ornamental horticulture;

Greg Hoover, senior extension associate

in entomology; and Gary Moorman,

proessor o plant pathology.

Visit Penn States College o Agricultural Sciences on

the Web:www.cas.psu.edu

Penn State College o Agricultural Sciences research,extension, and resident education programs areunded in part by Pennsylvania counties, the Com-

monwealth o Pennsylvania, and the U.S. Depart-

ment o Agriculture.

Tis publication is available rom the Publications

Distribution Center, Te Pennsylvania State Univer-

sity, 112 Agricultural Administration Building, Uni-versity Park, PA 16802. For inormation telephone

814-865-6713.

Where trade names appear, no discrimination is

intended, and no endorsement by Penn State Coop-

erative Extension is implied.

Tis publication is available in alternativemedia on request.

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the policy that all persons shall have equal access

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Produced by Ag Communications and Marketing

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Some Selected References

Batdor, L. R. Boxwood Handbook.

Boyce, Va.: American Boxwood Society,

1995.

Dirr, M.A. Manual o Woody Landscape

Plants: Teir Identifcation, Ornamental

Characteristics, Culture, Propagation andUses. Champaign, Ill.: Stipes Publishing

Company, 1998.

Hamilton, C. C. Insect Pests o

Boxwood. New Jersey Agricultural

Experiment Station, 1935.

Moorman, G. W., W. K. Hock, and G.

A. Hoover. Woody Ornamental Insect,

Mite, and Disease Pest Management.

University Park: Te Pennsylvania StateUniversity, 2000.

Johnson, W. ., and H. H. Lyon. Insects

that Feed on rees and Shrubs, 2nd ed,

rev. Ithaca, N.Y.: Cornell University

Press, 1991.

Larson, P. D. Boxwood, Its History,

Cultivation, Propagation, and

Descriptions. Boyce, Va.: Foliar Press,

1998.

Rel, D., and B. Appleton. Boxwood in

the Landscape. Virginia Cooperative

Extension, 2001.

Saunders, P. M. Best o the Best:

Boxwood Cultivars Manual. Piney River,

Va.: Saunders Brothers, Inc, 2001.

Schread, J. C. Boxwood Pests and Teir

Control. Connecticut Agricultural

Experiment Station, 1953.

Documents

Boxwoods