Eastern Arborvitae, Arborvitae, American Arborvitae, or White Cedar

(Cupressaceae - Cypress Family)

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• Form
  • small, medium, large, or very large evergreen shrub, depending upon cultivar
  • often maturing at about 20' tall by 8' wide in urban landscapes; however, the species form and larger cultivars can slowly get much bigger over time, to 50' tall by 15' wide, while dwarf cultivars can mature at 3' in height with a slightly wider width
  • upright pyramidal, upright columnar, or rounded growth habit, depending upon cultivar
  • slow growth rate

• Culture
  • full sun to partial sun
  • prefers a moist, well-drained, loamy soil in full sun, but tolerates soils that are poor, rocky, clay, compacted, dry, and of various pHs extremely well, and is very urban tolerant to heat, drought, humidity, and pollution; however, not tolerant of shady situations
  • propagated primarily by rooted stem cuttings
  • Cypress Family, with several potential diseases and pests, most of which rarely manifest themselves; however, one annual pest (bagworms, which cause minor to major feeding damage to the new foliage) and one longterm disease (heartwood rot of the interior wood, which leads to a decline in vigor with maturity) are noteworthy
  • abundantly available in ball and burlap or container forms, with many cultivars
  • very prone to having its vertical branches permanently separated in the upper canopy when under ice or wet snow loads, due to the very flexible and lightweight wood with dense evergreen foliage that catches and retains the heavy Winter precipitation
  • the cultural practice of tying together the upper canopy to support the shrub under snow or ice loads is often practiced, but care should be exercised with the width and coating of the tying device (wide rope, plastic-coated clothesline, or rubber straps, rather than bare wire or thin twine) as well as the type of "tie" that is practiced (a U-shaped loop around the branches, anchored in similar fashion to other branches or tightly tied to a driven stake, rather than circular tight knots) will properly support the growing branches for years to come, as opposed to constricting the branches, slowly killing them, and ruining the entire shrub

• Foliage
  • sprays of scale-like, dark green, miniature leaves are evergreen and held so tightly against the stems that the young twigs are often completely hidden
  • old foliage from the self-shaded middle of the shrub abscises noticeably in Autumn, and falls through the interior of the canopy directly to the ground below, forming a light brown carpet that is easily raked up
  • the remaining foliage on most of the cultivars turns to an unnattractive chartreuse-brown in the coldest portions of Winter, but thankfully returns to medium- or dark green by late March
  • foliage is highly scented if sheared

• Flowers
  • monoecious and ornamentally insignificant in April

• Fruits
  • the small green to chartreuse clustered cones of about 1/3" long often go unnoticed in Summer, maturing to brown in early Autumn and spreading their scales widely apart to release the small seeds

• Twigs
  • brown but covered with green scaly foliage for the first two or three years, forming sprays of stems in the same general plane of the branch

• Trunk
  • brownish-red bark exfoliates on mature branches or trunks, but is often hidden by the foliage of lower branches
  • some forms are single-trunked or few-trunked, with lateral branches, while other forms are few- to many-trunked, with strongly ascending branches
  • wood is lightweight but extremely prone to permanent bending under the weight of Winter wet snow or ice, and often the upper canopy of shrubs will separate under such loads and expose the unnattractive barren stems of the once-interior canopy

• ID Summary
  • scale-like sprays of miniature evergreen foliage cover the stems of this generally columnar shrub, which is usually multitrunked with branches that can be easily separated in the upper canopy to reveal the bare interior branches
  • the other common species of Arborvitae, Thuja orientalis, usually has foliage and stems that separate into vertical pleats, and is not quite as vigorous, nor nearly as cold-hardy

• Function
  • foundation, informal hedge, entranceway, privacy screen, non-thorny barrier, or specimen shrub, often overused

• Texture
  • medium-fine texture
  • thick density

• Assets
  • very urban-tolerant evergreen shrub (especially to heat, drought, and poor soils)
  • foliages to the ground even at maturity (unless it is limbed up into tree form)
  • responds well to continuous shearing (although it is rarely needed, except when it exceeds the height or width for which it was originally intended)
  • cold hardiness (to zone 2)

• Liabilities
  • Winter evergreen foliage color is often an unattractive yellow-brown
  • very prone to bagworms and their feeding damage
  • very prone to branch separation under snow and ice loads
  • widens at its base with age, or separates into several leaning but divergent canopies with age (this applies to both upright and rounded cultivars)
  • does not recover from severe pruning (where the bare stems are exposed, although side branches may slowly envelope the dead stems)
  • interior foliage noticeably sheds in Autumn

• Habitat
  • zones 2 to 8
  • native to portions of the Eastern United States

• Alternates
  • evergreen shrubs, especially those with an array of species or cultivars that are columnar, upright oval, pyramidal, or globed (Juniperus, Ilex, Picea [dwarf forms], Taxus, etc.)

• Variants
  • many exist, selected for their growth habit, height and width, Summer foliage color (a few are gold-tipped), and healthy green Winter foliage color; some of the most common cultivars are listed below:
  • Thuja occidentalis 'Hetz Midget' - globed form, to 3' tall by 3' wide
  • Thuja occidentalis 'Nigra' - upright columnar form with dark green Winter foliage, to 20' tall by 4' wide
  • Thuja occidentalis 'Peabody' - golden-foliaged, broad-pyramidal form, to 10' tall by 5' wide, best placed in full sun (where it does not burn), with the foliage bronzing in Winter
  • Thuja occidentalis 'Pyramidalis' - narrow pyramidal form that is very subject to Winter burn, to 15' tall by 4' wide
  • Thuja occidentalis 'Rheingold' - unusual copper-orange to yellow-brown foliage year-round, with a distinctly different awl-type of foliage resembling a dwarf Juniper, globed in shape and slowly growing to 5' tall by 4' wide
  • Thuja occidentalis 'Smaragd' (also known as 'Emerald' or 'Emerald Green') - rapidly becoming the most popular cultivar, a relatively new introduction having emerald green foliage that retains its vibrant green color throughout the Winter, with very dense foliage held in somewhat short vertical scalloped sprays, narrowly pyramidal to columnar in growth habit, to 12' tall by 3' wide
  • Thuja occidentalis 'Techny' (also known as 'Mission') - the long-standing traditional cultivar that has dark green foliage year-round, to 12' tall by 4' wide, broadly pyramidal or upright oval in shape

• Translation
  • Thuja is the Greek name for Juniper, another common evergreen shrub or tree.
  • occidentalis translates as "western", referring to it being native to the Western Hemisphere.

• Purpose
  • Eastern Arborvitae is a commonly utilized evergreen shrub with numerous cultivars, useful in many urban stess situations where a low-maintenance evergreen shrub is required.

• Summary
  • Thuja occidentalis is a common evergreen shrub, having cultivars that are narrow pyramidal, columnar, or globed in shape, often found at entranceways, at the corners of foundations, or as privacy screens in row plantings.