 |
 |
|
|
|
by. Dr. William R. Chaney
|
|
|
|
|
| The name arborvitae or "tree of life" dates from the 16th century and
the French exploration of the Saint Lawrence River. Jacques Cartier
learned from the Indians along the river how to boil the tree's branches
and foliage to make a concoction that was rich enough in vitamin C to treat
the scurvy afflicting members of his expedition. In gratitude
for curing their sickness, the French carried the tree home in 1534 where
it was named “l’arbor de vie” by the King of France and planted in medicinal
plant gardens. As a consequence, eastern arborvitae is thought
to be the first American tree introduced to Europe. Even today an
over-the-counter elixir made with arborvitae extracts is used to treat
the common cold.
There are only six species in the Thuja genus, two in North America and four native to eastern Asia. The native range of eastern arborvitae (Thuja occidentalis) is the southern part of the eastern half of Canada and the adjacent northern part of the U.S., extending south to western North Carolina and eastern Tennessee in the Appalachian Mountains in U.S.D.A. Hardiness Zones 3b-7b. Lumbermen call this tree northern white cedar and wonder why arborists, who prefer the name eastern arborvitae, can’t recognize a cedar when they see it. The other North America species, western red cedar (Thuja plicata) is found in the northwestern U.S. and southwestern Canada. This species can attain gigantic proportions and is one of the four most important commercial species of the Pacific Northwest. |
||||
| Description | ||||
| Eastern arborvitae has a dense, upright, oval or conical shaped-crown
with short ascending branches arising along the trunk to nearly the ground-line.
It frequently branches into multiple upright trunks. The tree is
a slow growing evergreen that may live 300-400 years. Its twigs are
highly branched and flattened in a horizontal plane, forming fanlike sprays.
The small scalelike leaves are shed with the twigs after several years.
Most cultivars are preferable to the seedling-grown native tree because
its foliage tends to yellow badly in the winter. There is no cause for
alarm when the oldest foliage turns rusty red in the autumn since it is
a natural coloration prior to shedding of entire branchlets with attached
foliage. All evergreens drop some of their foliage every year, usually
in the fall when the leaves of deciduous hardwoods are colorful.
The attractive bark consists of a close network of fibrous ridges and furrows
that vary in color from gray to cinnamon-red.
Arborvitae is relatively shallow-rooted and isolated individuals are subject to windthrow and uprooting. In forest situations or when planted in dense screens or windbreaks some windfirmness may be the result of natural root grafts between adjacent trees. Because of their shallow position, the roots are easily exposed in lawns. Male and female flowers of eastern arborvitae, a monoecious species, are usually borne on separate twigs in the spring. They are tiny, non-showy, terminal, cone-like structures. Male flowers are yellowish and arise from branchlets near the base of shoots. Female flowers are pinkish and appear at the tips of short terminal branchlets. Ripe cones, which are pale cinnamon brown, mature in August to September and are up to 0.5 inch long. Similar to junipers in use and appearance, eastern arborvitae is distinguished from the junipers by their flattened branchlets. The resemblance between eastern arborvitae and Chamaecyparis (falsecypress) is so close that it can baffle an amateur plantsman. The common test is to look at the underside of the leaves. Those of Chamaecyparis show whitish marks, giving them a silvery appearance, whereas the leaves of an arborvitae are generally green on both sides. But the rule is not absolutely reliable for either species. |
||||
| Landscape Use | ||||
| Eastern arborvitae has received wide acceptance in landscaping as screens,
windbreaks, accent plants, or hedges and in fact has become stereotyped
for these uses. The tree also can be placed at the corner of a building
to soften or frame a view. Because of its upright shape and limited
crown spread, eastern arborvitae is one of the few trees recommended for
the outer edges of electric transmission rights-of-ways. Trees commonly
reach 40 to 50 feet all and 12 to 24 inches in diameter at maturity.
However, the American Forestry Association's record eastern arborvitae
found in Michigan measured 69 inches in diameter and 113 feet tall.
The rot- and termite-resistant wood is quite useful, principally for products in contact with water and soil. The decay resistance and durability of the wood of arborvitae bring it into urban settings as rustic fencing and posts or roofing shingles. The lightweight wood is strong even though ring shake, or separation of the annual growth rings, is common in standing trees. It splits easily into thin layers, the characteristic that accounts for ring shake in standing trees and the wood's use for shingles. For the same reason the wood was used in the past by native Americans to make ribs for canoes. Eastern arborvitae is particularly valuable in winter deeryard management as both cover and browse. The trees also provide excellent cover for birds, particularly warblers, white-throated sparrows, and kinglets. In large urban parks or estates where white-tailed deer numbers may be high, browsing of eastern arborvitae could be a problem. . |
||||
| Planting and Care | ||||
| Eastern arborvitae grows best on limestone-derived soils that are moist,
but well drained, and neutral to slightly alkaline, pH 6.5 to 7.5 being
most favorable. Native trees are usually found in moist woods, often
near or beside water although they do not tolerate prolonged flooding.
In urban settings where competition and fire are not a challenge, a wide
variety of organic and mineral soils yield trees of better form and volume
growth than natural stands. Nevertheless, eastern arborvitae does
not develop well on extremely wet or dry sites, but once established arborvitae
will tolerate considerable heat and drought.
Eastern arborvitae propagates readily from cuttings and is easily transplanted from containers or balled and burlapped. It needs little pruning to develop good structure. Although the species is rated as shade tolerant, it will become thin and open with poor vigor unless exposed to considerable sunlight, but at the same time in areas sheltered from wind and where humidity is high. The thin bark has a high oil content, accounting for its high susceptibility to fire damage. Snow and ice often damage arborvitae by accumulating on the dense foliage and breaking limbs. Trees are often bent into a permanent leaning position by the weight of ice and snow. Desiccating winter winds and low temperature, deicing salts, and drought can turn arborvitae foliage yellow or brown and sometimes cause severe damage or death. The tree’s tolerance to deicing salts is only moderate, so branches exposed to salt spray along highways commonly have severe dieback. The high salt content of dog urine too can cause unsightly browning of the foliage. Eastern arborvitae is tolerant of moderate ozone levels in urban areas and of phenoxy herbicides such as 2,4-D used to control weeds in lawns. The worst defect of eastern arborvitae is that in winter its color turns yellow or even brownish. As a consequence, there has been a lot of research to develop varieties that will remain vigorously green through the winter. |
||||
| Cultivars | ||||
There is a lot of genetic variability in eastern arborvitae as indicated
by the very large number of cultivars available, more than 120, but only
a few deserve real attention. The species may be found represented
by the thinnest of columnar forms, broad pyramidal shapes, and low globose
types that are truly shrubs. The many variations of foliage include
some that are golden or white. ‘Emerald’, ‘Nigra’, and ‘Techny’ are excellent
cultivars that hold their green color through the winter. ‘Brandon’
is an unusually cold-hardy form selected for the Canadian prairies and
valued as well in the northern prairies of the U.S. ‘Wareana’ has
large, dull blue-green leaves, making a heavy foliage mass. It is
very effective as a screen and is probably the most drought-tolerant cultivar
of Thuja occidentalis. 'Sunkist' is an exceptionally good, attractive
yellow form that is now often planted. Many of the smaller forms
such as ‘Ericoides’, Hetz Midget’, Little Gem’ and ‘Umbraculifera’ are
collector’s items or suitable for small scale landscapes or rock garden
situations.
|
||||
| Disease and Insects | ||||
| Unfortunately eastern arborvitae is susceptible to a few insect and
disease problems, some of which require control when infestations occur.
Bagworm (Thyridopteryx ephemeraeformis), juniper scale (Carulaspis carueli),
and spruce spider mite (Oligonychus ununguis) can significantly damage
ornamental arborvitae. Bagworms can devour large quantities of foliage
very quickly. Although less problematic, heavy infestations of the
Fletcher scale (Lecanium fletcheri), arborvitae aphid (Cinara tujafilina),
and arborvitae weevil (Phyllobius intrusus) can occur in the landscape
as well as in nurseries. Larvae of the northern cedar bark beetle
(Phyllbius intrusus) may occasionally girdle trees by chewing into the
inner bark and wood.
Carpenter ants can be serious pests, but their occurrence is sporadic and seem to be more of a problem in forest trees. The black carpenter ant (Camponotus pennsylvanicus) attacks the heartwood of living trees, making them subject to windbreakage. The red carpenter ant (C. ferrugineus) also can cause significant damage. Outbreaks of the arborvitae leafminer (Argyresthia thuiella) have severely damaged natural stands of arborvitae as well as ornamental plantings and nursery seedlings. The larvae of several leaf-notching weevils (Otiorhyncus sp.) damage arborvitae and may cause severe damage to seedlings in nurseries. Although eastern arborvitae has few serious diseases as a forest tree, in cultivation it is subject to several seedling and foliage diseases. The foliage blight fungi Phomopsis juniperovora, Didymascella thujina, and Fabrella thujina are among the main organisms causing diseases of seedlings and young trees, but may occur on trees of all ages. A snow-blight fungus (Phacidium sp.) may cause important damage in nurseries and hedges. Although several root- and butt-rot fungi including Poria subacida and Phaeolus schweinitzii attack arborvitae, they mainly attack old or damaged trees. When no conks show on the bowl to indicate heartrot, woodpecker workings indicate that the tree is infected. For this species, woodpeckers tap only trees with heartrot. Landscapers like to plant eastern arborvitae because of its unusual scalelike foliage, flattened branchlets, and crown pattern. Although the native eastern arborvitae may have features that reduce its landscape and ornamental attractiveness, the many cultivars now available were developed to overcome those faults. As a result, eastern arborvitae is an especially appealing tree to use and enjoy today. |
| Staff | Publications | Program Areas | Contact Us |
