Canadian Hemlock, Hemlock, or Eastern Hemlock Tsuga canadensis

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FEATURES

* Form
o naturally a large evergreen specimen or shade tree; however, under cultivation, a small-, medium-, or large-sized evergreen shrub or tree (depending upon site conditions, cultural treatment, and/or cultivar)
o species form matures to at least 80' tall by 40' wide in its native habitat, but it is normally a much smaller tree under urban conditions (to 25' tall by 10' wide, as a general rule)
o upright pyramidal growth habit
o medium growth rate, sometimes with a second flush of growth later in the growing season (a slow growth rate is often achieved under urban stress conditions, or for the numerous dwarf shrub cultivars)

* Culture
o full sun to full shade
o Canadian Hemlock can be quite finicky in its exacting requirements for transplant success:
+ best performance occurs in an evenly moist but very well-drained soil, which is rich in organic matter and acidic to neutral in pH, lightly mulched to maintain a cool root zone, and sited in partial sun to partial shade conditions; however, it tolerates full sun to full shade and acidic to alkaline pH soils
+ physiologically, this species generally does not tolerate nutrient-poor soils, wet soils or poorly drained sites, prolonged drought, prolonged heat, sunscorch, windy and exposed sites, aerial pollution, or Winter salt spray (most of the above conditions can occur when it is sited as a foundation tree or as a roadside screen planting)
o species form is propagated by seeds or rooted stem cuttings, while cultivars are often grafted onto species rootstock
o Pine Family, with numerous potential disease and pest problems that affect the roots, bark, wood, or foliage, but a major problem for this species down the road may be the adelgid pest, which has devasted the species in some areas of its native habitat
o abundantly available in ball and burlap form, and increasingly in container or field pot form
o if allowed to grow naturally from the start, it has quite an open growth habit in youth that fills in with age, but it is often repeatedly sheared at the nursery (or Christmas tree farm) to promote a dense canopy effect when it is sold
o Canadian Hemlock is somewhat sensitive to being transplanted in Autumn, and care should be taken to amend the soil, fertilize, water thoroughly, mulch adequately, and avoid Winter salt spray, to enhance survival chances during the first Winter
o in addition, good water drainage is essential for transplant success, and the site soil should be amended (if necessary) with peat moss or sand to improve its porosity, with the root ball elevated about 2" to 4" above the surrounding soil grade, followed by light mulching, to optimize the moisture requirements of the sensitive and re-establishing root system
o Hemlock should be regularly watered (but not overwatered, which will lead to root rot) during its first year after transplanting, to prevent the amended soil and original root ball from drying out
o due to its densely sheared evergreen canopy, Hemlock should be staked for the first two or three years following transplanting, to prevent windthrow during the rooting-in period

* Foliage
o the evergreen, medium- to dark-green needles are about 0.5" long, subtlely petioled, and in a spiraled or pectinate (two-ranked) arrangement on the slender stems, with two bluish-white bands underneath each needle

* Flowers
o ornamentally insignificant; staminate flowers in axillary catkins, and pistillate flowers in terminal conelets

* Fruits
o 0.5" miniature cones are initially green, becoming brown in their second year, quite attractive when viewed up-close on the branches, but not ornamentally significant

* Twigs
o thin, green-brown, and pubescent, with slightly drooping branch tips (the branch tips will droop much more if it is under drought stress from Spring transplant shock)
o terminal branch tips and the central leader have long, slender, relatively unbranched and open growth when allowed to grow naturally, but are much more dense when they are periodically sheared

* Trunk
o scaly to flakey and red-brown on young trees (seldom seen, as the young tree is allowed to branch to the ground), but becoming dark brown to gray and furrowed/ridged with age, and quite noticeable if the tree is limbed up

* ID Summary
o small evergreen needles and thin wispy horizontal stems that turn down at the ends combine to yield a very fine-textured and gracefully branching pyramidal tree, often sheared for density in nursery production and utilized in shady spots as a specimen, screen, or group planting evergreen tree

USAGE

* Function
o correctly used as a specimen, screen, or group planting small tree, in wind-protected sites in partial sun to partial shade; with discretion, it can also be used as a foundation shrub
o the species form can alternatively be sheared over time into a formal evergreen hedge, which is very dense and foliages all the way to the ground (due to its full shade tolerance)
o often incorrectly used as a windbreak in exposed sites (where it exhibits dieback from Winter winds), as a roadside screen planting (where it is severely damaged from Winter salt spray), or as a foundation shrub (where, with proper care, it eventually gets far too big for its site, unless it is annually pruned or sheared to keep it in-bounds)

* Texture
o very fine-textured
o thick density (except in youth, when it is rarely found natural and unsheared in an open density state)

* Assets
o ultra-fine texture (a combination of the miniature-needled foliage and the slender, horizontal to drooping twigs)
o pyramidal growth habit
o branches and foliages to the ground
o grows in full shade to full sun conditions
o can be repeatedly sheared for a dense tree or dense hedge effect

* Liabilities
o often has chlorotic/sunscorched foliage or dieback when placed under urban stress conditions (especially full sun, drought, poor soils, heat, and/or salt spray)
o does not tolerate poorly drained soils or wet sites
o the adelgid pest is ravaging Hemlock in portions of its native habitat, and may spread to urban areas in the future
o somewhat overused because of its fine texture and sun/shade adaptability (use Chamaecyparis nootkatensis 'Sullivan' as an alternative)

* Habitat
o zones 4 to 7
o native to Eastern Canada and Appalachia

SELECTIONS

* Alternates
o evergreen pyramidal trees (most species of Abies, Picea, Pinus, etc.)
o evergreen conifers of fine- to medium-fine texture (Abies koreana, Chamaecyparis species, Picea orientalis, Pseudotsuga menziesii, Thuja occidentalis, etc.) or deciduous conifers of similar texture (Larix, Metasequoia, Pseudolarix, & Taxodium)
o full-shade tolerant evergreen large shrubs or trees (Chamaecyparis lawsoniana, Chamaecyparis nootkatensis, Tsuga caroliniana)

* Variants
o Tsuga canadensis 'Beehive' - a dwarf shrub to 3' tall and 5' wide, with the general shape of a spreading beehive
o Tsuga canadensis 'Bennett' - another dwarf shrub to 3' tall and 5' wide, with ascending then arching upper branchlets, preferring partial shade
o Tsuga canadensis 'Cole's Prostrate' - a groundcover form and bonsai alternative in partial shade to the prostrate Junipers, slowly to 1' tall by 4' in diameter, with the central stems becoming exposed over time
o Tsuga canadensis 'Gentsch White' - a dwarf shrub form (to 4' tall by 4' wide if never pruned, but half that size when sheared), with Spring tip growth that becomes intensely creamy-white in Autumn and Winter against the dark green background of the older foliage; must be placed in partial shade to avoid sunscorch; feather shearing is recommended to promote compactness and encourage more tip growth
o Tsuga canadensis 'Jeddeloh' - a dwarf shrub form to 3' tall by 5' wide, with a subtle depression in the center, and an alternative to Bird's Nest Spruce (Picea abies 'Nidiformis')
o Tsuga canadensis 'Pendula' - an upright weeping form, often staked during nursery production to maintain a central leader to the desired height, often anywhere from 2' to 5' tall, by about 5' wide
o Tsuga canadensis 'Sargentii' - a wide-spreading and weeping large shrub form, to 10' tall by 20' wide, with many pendulous branches, effectively used near bodies of water (where it resembles a "green ghost"), in large rock gardens, or on embankments

NOTES

* Translation
o Tsuga is the Japanese name for one of the Asian Hemlocks.
o canadensis translates as "from Canada", where it is native.

* Purpose
o Canadian Hemlock is a very fine-textured evergreen tree, branching naturally to the ground and one of the few evergreens ideally suited for shady sites.

* Summary
o Tsuga canadensis is a graceful, fine-textured, shade-tolerant evergreen tree that performs best in cool and moist northern climates, effective in groups or as a specimen tree, with several interesting shrubform cultivars.

Contact Information

Department of Horticulture and Crop Science,
The Ohio State University
202 Kottman Hall
2021 Coffey Road
Columbus, OH 43210

Phone: 614-292-1809
Fax: 614-292-7162
Email: Randle.15@osu.edu

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