Growing Boxwoods 1976 -- National Arboretum Agricultural Research Service Home and Garden Bulletin...|
Growing Boxwoods |
Agricultural Research Service
Home and Garden Bulletin 120, USDA, 1967.
Slightly revised January 1976
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HOME AND GARDEN BULLETIN N0.120- U.S. DEPARTMENT OF AGRICULTURE
Boxwoods have been cultivated in
the Middle Atlantic States from colo-
nial times. The center of climatic ad-
aptation for boxwoods is the Chesa-
peake Bay region and the foothills of
the Blue Ridge in Virginia and North
Carolina. Fine specimens are also
found in the Piedmont of South Caro-
lina, in Tennessee and Kentucky, in
the vicinity of Delaware Bay, on Long
Island, N.Y., and on the Pacific coast.
SPECIES AND VARIETIES
The two most widely cultivated
boxwood varieties are the English box
and the common box. Both are mem-
bers of the botanical species Buxus
sempervirens. The English box, or B.s.
suffruticosa, is a dwarf shrub, often
less than 3 feet tall at maturity. The
common box, or B.s. arborescens, is
larger, usually attaining the height of
a small tree. Both have standard box-
wood characteristics: Dense foliage
and full, rounded shapes.
Some other forms of the species B.
• Weeping box—a tall boxwood
with drooping branches and wispy fo-
liage. Example: B.s. pendula.
• Fastigiate box—a narrow, upright
type particularly suitable for hedges.
Example: B.s. fastigiata.
• Variegated box—a shrub that has
leaves mottled or bordered with white
or light yellow. Example: B.s. argen-
Other species of boxwood, in addi-
tion to B. sempervirens, include B. bal-
earica, B. harlandii, and B. micro-
phylla. Two hardy plants, the Japa-
nese box and the Korean box, are
members of the species B. microphylla.
B. balearica plants are somewhat
scarce, but the other species are avail-
able from nurserymen.
Boxwood varieties differ in their
ability to resist cold weather (see plant
hardiness zone map, p. 3). Boxwood
culture is almost impossible in areas
where temperatures drop to —10° F.
or lower. The dry, cold winters of the
Midwest are unsuitable for boxwood
SITES AND SOIL
Boxwoods are tolerant of shade and
are often planted in heavy shade adja-
cent to walls or under tall trees. They
also do well in full sunlight. An ideal
site would provide full sunlight during
part of the day and mottled shade at
A wide range of soil types, from
sandy loam to heavy clay, are suitable
The USDA plant hardiness zone map. English box and common box can be grown
best in zone 7. Japanese box can be grown in zone 6, and the even hardier Korean
box can be grown in the southernmost portions of zone 5. Many varieties can be
grown in the warm climates of zones 7, 8, and 9, but zones 4 and lower are too cold
for any of the boxwood varieties.
for boxwoods. Soil texture is impor-
tant only as it influences moisture-
holding capacity. Best growth is made
in fairly heavy clay that is well sup-
plied with organic matter.
Boxwood soil must be well drained
and aerated. If the planting site has
no natural drainage, boxwoods can be
"planted high"; that is, the hole for
the rootball can be made shallower
than the depth of the rootball. Earth
can then be built up around the, pro-
truding rootball to provide a sloping
surface. This improves drainage
around the base of the plant.
Acid soils and lime-rich soils are
both satisfactory for boxwoods; the
plants thrive in either.
PREPARATION OF SOIL
If the planting site is suitable for
boxwood culture, little preparation of
soil is necessary before planting. Make
a hole big enough to accommodate the
rootball. If the excavated soil is stiff
and lumpy, put it aside and use woods
soil or topsoil. If good topsoil is not
available, mix bonemeal or commer-
cial fertilizer with the excavated soil.
The boxwood is a heavy-feeding
plant and will grow rapidly if liberally
fertilized. If its root system is well es-
A full, billowing shape characterizes mature boxwood plantings.
tablished, it will make some growth
even if soil is of low fertility.
Do not rely on winter mulches to
supply all of the nutrients needed by
boxwoods. Some boxwoods—particu-
larly trees and large shrubs—may lack
vigor if fed entirely by surface mulch.
You can prevent this lack of vigor by
sprinkling commercial fertilizer
around the base of each plant. Use
fertilizer grade 10-6—4. Apply 1 to 2
pounds per 100 square feet of soil sur-
Apply fertilizer in late fall just be-
fore the ground freezes, or as soon as
the ground thaws in the spring. Ferti-
lizing in early fall may delay the ma-
turing of the shoots and may promote
second growth, which will be subject
Boxwoods need the equivalent of
about 1 inch of rainfall every 10 days.
You can be safe in watering plants
thoroughly every 10 days from spring
to midsummer. Omit watering for 10
days after heavy or prolonged rains.
From midsummer on, water spar-
ingly—every 2 to 3 weeks. If fall
weather is dry, water the plants heav-
ily just before the first freezing
weather is expected.
If drought persists into winter,
BN-36203, BN-36262, BN-36261
Some of the variation in boxwood leaves: Top, variegated box;
bottom left, common box; bottom right, English box.
water the plants every 2 to 3 weeks
during the winter, whenever the
ground is not frozen.
Boxwood foliage is very dense.
Outer shoots should be pruned so that
inner shoots can get light and air.
Small shoots should be pruned at
their juncture with larger branches. If
large branches must be removed,
standard precautions should be ob-
served: The cut should be close and
clean; the bark should be bruised as
little as possible; and cut surfaces of a
square inch or more should be
promptly coated with shellac followed
by tree paint.
At least once a year, remove debris
(leaves, twigs, etc.) that has accumu-
lated in your boxwoods. Much of it
will come out if you shake the bushes
vigorously. Pick out the rest. If debris
is not removed, it may promote fungus
Boxwoods can be transplanted at
any time except when they are in
active growth or when the ground is
Rootballs should be large and solid.
Dwarf boxwoods require a rootball
with a diameter at least half the diam-
eter of the top of the plant. Tree box-
woods should have a rootball with a
diameter at least one-third the height
Plants 2 to 3 feet high or broad
should be shaded for a year after
transplanting. A lattice that cuts off
about half the light should be used.
Shading is especially important if the
plants are moved from a partly shaded
Boxwoods may need winter covers. In
mild climates, pine branches placed
along the north side of hedges will pro-
vide adequate protection.
to an exposed site. The lattice should
clear the foliage by 10 to 18 inches
and should protect at least the sunny
sides as well as the top of the plant.
Newly transplanted boxwoods must
be watered thoroughly and regularly.
Direct a slow flow of water under-
neath the crown to the trunk. Con-
tinue watering until the rootball is wet
all the way through. Build a low ridge
of soil around the rootball to prevent
wasting water and to allow thorough
In areas ideally suited for boxwood
culture, a mulch of wood chips, leaf
mold, or similar material provides ad-
equate protection to boxwood plants
during the winter. A mulch protects
by preventing rapid temperature
change at the soil surface, deep pene-
tration of frost, and excessive loss of
Additional protection is needed in
areas where the winter temperature is
likely to be colder than 20° F. In these
areas, some covering is necessary for
the top of the plant.
The covering can be made of bur-
lap, a section of snow fence, or any
other material that will protect the
top, yet permit air circulation around
the plant. The foliage should not rub
against the covering.
Do not put the cover on until the
ground surface freezes; take it off as
soon as the risk of temperatures colder
than 20° F. is past. Mild frosts after
removal of covers do little harm.
Diseases of boxwoods can be di-
vided into three classes: Those that
attack the leaves, those that attack the
stems and branches, and those that
attack the roots. All of these diseases
are caused by fungi.
Snow accumulation sometimes breaks down the branches of small boxwood shrubs.
This means of support—cords strung along the sides and crisscrossed through the
interior of shrubs—helps prevent such damage.
Boxwoods grow in a variety of forms. Pic-
tured on these pages are:
A, a common, or "tree" box. This one is
about 5 feet tall; the common box may
grow to a height of 30 feet.
B, a weeping box, with drooping branches
and wispy foliage.
C, a variegated box the leaves are edged
with pale, yellow-green markings.
D, a boxwood with extreme fastigiate
E, a typical planting of young English box.
The two most widely cultivated boxwood
varieties are the common box and the
English box. They have been grown
in the Middle Atlantic States since colo*
nial times, and their range now extends
westward to the Pacific coast (see zone
The other boxwoods pictured are a few of
the many horticultural varieties that
have been named by nurserymen. For-
mal classification of boxwood is diffi-
cult. Consequently, a given variety may
have different names in different
Leaf diseases result in spotted or
discolored leaves. Fungus pustules
usually appear on the leaves. Leaf dis-
eases can be controlled by spraying
from one to four times with Bordeaux
mixture. The first spray application
should be made in the spring, before
plant growth begins; the second, when
new growth is about half completed;
A, leaf fungus. B, twig fungus. Fungi
usually develop only on weak or in-
jured plant parts.
the third, about 3 weeks after the
second; and the fourth, in the fall
after growth has ceased.
Some symptoms of stem disease are
loss of color in the leaves, develop-
ment of spore pustules in the bark,
and loosening and peeling of bark.
Most stem diseases can be controlled
by pruning the diseased parts or goug-
ing out the diseased areas. Pruning
should be done before humid summer
weather arrives and promotes further
growth of fungus spores. As a preven-
tive measure, remove all debris from
the interior of the plant. Shake bushes
vigorously and go over them with a
broom or vacuum cleaner.
Root rot affects many plants in ad-
dition to boxwood, and is very difficult
to control once it becomes established.
Good cultural practices will help pre-
vent infection. Good drainage around
the roots is especially important. If
boxwoods die of root rot, the roots
should be dug up and the soil steri-
lized before new trees are planted.
INSECTS AND RELATED
The principal pests of boxwoods are
the boxwood leaf miner, the boxwood
psyllid, the boxwood mite, and oyster-
shell scale. Pesticides named in this
section kill pests present in old foliage
and protect new foliage from infesta-
tion. Local conditions may influence
spraying requirements; if you want
advice about spraying, get in touch
with your county agricultural agent.
Boxwood Leaf Miner
The boxwood leaf miner is the larva
of a small gnatlike fly. In spring, the
. , BN-36259, BN-36258, BN-36265, BN-36260
A, the orange-colored adult, or fly, of the boxwood leaf miner. B, a miner-infested
leaf; the arrow points to the thin spot through which the adult fly will emerge.
C, leaf miner maggots, exposed by removing the surface membrane of the leaf
D, pupal skm hanging from the undersurface of the leaf. The adult fly has emerged
from the skin.
flies inject their eggs into the young
boxwood leaves. Larvae from the eggs
develop slowly during the summer,
hollowing out areas inside the leaves
as they feed. They winter inside the
The larval, or feeding, stage of the
life cycle is completed late in April or
early in May. The pupal stage follows;
it lasts about 10 days. During this
stage, the larvae turn to pupae. The
pupae break through the surfaces of
the leaves and work themselves part-
way out. The adult flies then emerge
from the pupae.
Adults of this insect are easily con-
trolled with properly-timed applica-
tions of carbaryl. To determine the
right time to apply carbaryl, watch the
development of the pupae. Every 2 or
3 days during the pupal period, break
open a leaf and examine the pupae.
A pupa's head and wing pads turn
dark brown near the end of the pupal
period—just before the adult fly
emerges from the leaf. This is the time
to apply carbaryl.
To control the leaf miner when in
the young larvae stage, spray with car-
baryl about June 15 just after they
hatch. Spraying later in the summer
or autumn also controls the larvae,
but their mines will remain as yellow
spots in the leaves.
Dimethoate sprays will control ma-
ture larvae if applied in early spring as
plants resume growth.
The adult boxwood psyllid is a
grayish-green sucking insect about
one-eighth inch long. In its preadult
(nymph) stage, the psyllid feeds on
leaves and causes the characteristic
leaf-cupping deformity on young
Boxwood foliage infested with psyllids.
Note the excreted white material and
the cupping of leaves.
spring growth. The nymph also ex-
cretes a white waxy substance. In late
May and early June the nymphs be-
come adults. The adults feed 6 to 7
weeks, then deposit their eggs at the
base of overwintering buds. The eggs
hatch between August and October.
The newly hatched nymphs are
oval, legless, and scalelike in appear-
ance. They feed by inserting their
thin, hair-like mouth parts into the
live tissues of the plant and hibernate
in this stage under the bud cover. In
spring, usually about mid-April, they
molt, grow legs, and crawl to new
leaves to feed. To control nymphs,
spray with malathion in early spring
when new plant growth starts and
again about May 15. Spray again
about June 15 to control adults.
The boxwood mite is found in most
boxwood plantings. The adults are yel-
lowish green to reddish brown and
about one-sixty fourth inch long. Eight
or more generations may be hatched
during the spring, summer, and fall.
The last generation to mature in the
fall lays eggs that remain dormant
during the winter and hatch in mid-
Newly hatched mites feed first on
adjacent leaf tissue, then move from
leaf to leaf. The adult mites feed
mostly on tender shoots and on the
upper surfaces of leaves. Leaves at
first show tiny scratchlike markings;
later they become bronzed and with-
ered, and sometimes drop to the
ground. Dicofol and dimethoate, ap-
plied about May 15 and again June
15, will control most mite infestations.
If infestations are extremely heavy,
spray once every 2 weeks.
Oystershell scale attacks many kinds
of plants. This scale has a covering
shaped like an oyster. The covering is
brownish gray, one-eighth inch long,
and one-sixteenth inch wide. The
scale itself is yellow and soft bodied.
Healthy boxwoods have dense, lush foliage. Above, one of the specimens of common
box at Blandy Experimental Farm, Boyce, Va.
Scale eggs pass the winter under the
coverings of female scales. The eggs
hatch in May or June, and the
nymphs become adult scales by mid-
If large numbers of scales build up,
severe stunting or death of infested
branches may result. Prune heavily en-
crusted branches before spraying.
Apply dimethoate about June 15 to
control young scales. In addition,
apply a summer oil emulsion before
plant growth begins in the spring. Fol-
low the directions on the container
Boxwoods are attacked by several
species of plant-parasitic nematodes,
the most common of which are root-
knot nematodes, root-lesion nema-
todes, and spiral nematodes.
Root-knot nematodes enter the
roots and cause the root swellings, or
galls, that are usually called root-knot.
When infections are severe, plants
become stunted, foliage turns yellow,
and leaves fall. The plants may even-
Root-lesion nematodes enter the
root cortex and kill the cells on which
they feed. The damaged tissue is in-
vaded by bacteria and fungi, and the
roots rot. This stimulates formation of
new lateral rootlets above the dead
area, which in turn are invaded by the
nematodes. The result is an excessively
branched root system with the individ-
ual roots rotted or partly rotted.
Spiral nematodes feed with their
heads imbedded in the root tissue.
Cells of the root cortex are killed and
adjacent cells are affected by a sub-
stance secreted by the nematodes. The
result is an open wound that may be
invaded by bacteria and fungi.
If the roots are seriously damaged
by nematodes the plant will be unable
to get food and water, and will appear
sickly even when heavily watered and
Because nematodes are too small to
be seen without magnification, and be-
cause a number of other ailments
cause similar symptoms, nematode in-
festation is difficult to determine.
Treating Infested Plants
The chemical l,2-dibromo-3-chloro-
propane (DBCP) has been used with
CAUTION: This chemical may kill
boxwoods if too much is applied. Fol-
low the manufacturer's directions
Emulsifiable formulations of DBCP
are the most convenient. Bank up the
earth to form a basin around the
plant, then pour the chemical, mixed
with water, into the basin. Use enough
water to distribute the chemical evenly
Trade names are used in this publi-
cation solely for the purpose of provid-
ing specific information. Mention of a
trade name does not constitute a guar-
antee or warranty of the product by
the U.S. Department of Agriculture or
an endorsement by the Department
over other products not mentioned.
The pesticides mentioned in this publication are available in several different
formulations that contain varying amounts of the active ingredient. Because
of differences in active ingredient, dosage rates are not indicated in this publica-
tion. The user is cautioned to read and follow all directions and precautions
given on the label of the pesticide formulation that will he; used.
over the area of the basin. Add
enough water to fill the basin to a
depth of at least 3 inches. The chemi-
cal is effective only if enough water is
used. The water carries the chemical
down around the roots.
Do not apply DBCP when plants
are in active growth. The best time of
year for application is spring or early
fall. Soil temperature at a depth of 6
inches should be between 40° and 80°
F. during application.,
One treatment does not kill all ne-
matodes. Repeat the treatment as ne-
matode populations rebuild, but do
not repeat it more frequently than
once a year.
Before replacing a nematode-dam-
aged plant, treat the soil with DBCP
or some other nematode killer. Exam-
ine the roots of the replacement plant
for nematode damage. Do not buy ne-
matode-infested plants. Such plants
seldom thrive, even in fumigated soil.
Federal and State regulations require
registration numbers on all pesticide
containers. Use only pesticides that
carry this designation. Read and follow
all directions on the label.
USDA publications that contain sug-
gestions for the use of pesticides are
normally revised at 2 year intervals. If
your copy is more than 2 years old, con-
tact your Cooperative State Extension
Service to determine the latest pesticide
The pesticides mentioned in this
publication were Federally registered
for the use indicated as of the issue date
of this publication. Because the regis-
tration of a pesticide that you have had
in your possession for some time can be
changed, you may wish to check with
your local agricultural authorities to
determine the registration status of the
Information for this publication was furnished by
National Arboretum, Agricultural Research Service
This edition replaces all previous editions of this publication. Because of
changed insecticide recommendations, earlier copies should be destroyed.
Washington, B.C. Revised July 1971
Slightly revised January 1976
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