Common Name: Canadian Hemlock

General Information

Tsuga canadensis is an evergreen tree with a broadly conic, dense crown; it can grow up to 30 metres tall. The straight, cylindrical bole can be up to 150cm in diameter[, ].
The tree is commonly harvested from the wild as a commercial source of wood, which is considered to be of low quality and so is used especially as a source of pulp for making paper. It is occasionally planted for its timber in Germany[]. The bark has been a major source of tannins in the past, though is little harvested for this purpose at present. The tree also has a wide range of other uses as a food, medicine and source of materials. It is often grown as an ornamental, with many named forms available, and can be used as a hedge and ground cover.
This very widespread and abundant species occurs in many forests and woods. In parts of its range, mainly the southwest (Alabama, Tennesses, Kentucky), dieback that is caused by an invasive alien insect pest is spreading. Whether this pest is moving the species closer to extinction in the near future is uncertain as there is past (prehistoric) evidence of great fluctuations of Tsuga canadensis that were possibly caused by pest outbreaks, from which it recovered. The plant is classified as 'Near Threatened' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

None known

Botanical References

, ,

Range

Eastern N. America - Minnesota to Nova Scotia, south to northern Alabama and northern Georgia

Habitat

Woods and swampy areas on cool moist sites[], also in upland forests, often covering the north side of ridges[]. Moist rocky ridges, ravines, and hillsides; at elevations from 600 - 1,800metres [].

Properties

Conservation Status	Near Threatened
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	20.00 m
Growth Rate	Medium
Pollinators	Wind
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Tsuga canadensis grows in the cool, humid temperate zone of eastern N. America where the mean annual precipitation is around 700 - 1,500mm[].
An easily grown plant, it thrives best when growing in a deep well-drained soil in the more humid regions of the temperate zone, where it appreciates the higher rainfall[]. However, it succeeds in most soils and positions, being especially good on acidic sandy soils[] but also tolerating some lime[] so long as there is plenty of humus in the soil[]. In the wild plants are often found on highly acidic soils with a pH in the range 3 - 4[]. Plants are very shade tolerant when young, but need more sunlight as they grow older[, ]. Plants are thin and poor when grown in dry or exposed places[].
Seedlings grow slowly and cannot tolerate full sunlight until fully established, usually when they are 90 - 150cm tall[].
Tsuga canadensis is the most shade tolerant of all tree species and saplings may remain in the understory in natural stands for 25 - 400 years waiting for a gap to appear in the canopy and can then grow relatively quickly to exploit that gap[].
A slow-growing but long-lived species in the wild, with specimens nearly 1,000 years old recorded[]. It is very slow growing in cultivation for the first few years, it then grows more rapidly with annual shoots up to 60cm long. This rate of growth soon slows as the tree loses apical dominance and it becomes slow growing again[].
The tree has shallow, wide-spreading roots and casts a dense shade. Especially when growing in stands, it allows very little other plant life to flourish beneath it[].
The shallow root system makes trees highly susceptible to wind-throw when exposed through timber cutting or planted in open sites. Plants should be staked for the first two or three years following transplant in order to prevent wind-throw[].
Saplings and small trees are highly susceptible to damage from fire because of the thin bark, and root injury often also occurs from high intensity fires because of heavy litter concentration[].
Seed production commences around the age of 20 - 40 years, with good crops produced every 3 - 4 years[].
The crushed foliage has a sweet lemony scent[]. Another report says that it emits the unpleasant smell of hemlock[].
An insect pest introduced to N. America, the Hemlock Woolly Adelgid (Adelges tsugae) is causing substantial dieback in many areas, expanding from Virginia where it was apparently introduced in 1951 to the north and east. It has not yet reached the main area of occupancy around the Great Lakes. Moderating temperatures associated with climate change could allow the spread of this pest into areas where it has so far been prevented from infesting due to low winter temperatures[].
Many named forms have been selected for their ornamental value[]. Almost all of them are dwarf forms[].
Tsuga canadensis is the state tree of Pennsylvania[].
Plants in this genus are notably resistant to honey fungus[].

Edible Uses

Inner bark - raw or cooked[]. Usually harvested in the spring[], it can be dried, ground into a powder and then used as a thickening in soups etc or mixed with cereals when making bread[, , ]. An emergency food, it is only used when all else fails[].

The leaves and twigs yield 'spruce oil', used commercially to flavour chewing gum, soft drinks, ice cream etc[].

A herbal tea is made from the young shoot tips[, , , , , ]. These tips are also an ingredient of 'spruce beer'[].

Medicinal

Canadian hemlock was commonly employed medicinally by several native North American Indian tribes who used it to treat a variety of complaints[]. It is still sometimes used in modern herbalism where it is valued for its astringent and antiseptic properties.

The bark is rich in tannin and is astringent and antiseptic[, ]. A decoction is used in the treatment of diarrhoea, colitis, diverticulitis and cystitis[].
Externally, the bark is used as a poultice to cleanse and tighten bleeding wounds, as a douche to treat excessive vaginal discharge, thrush and a prolapsed uterus, and as a mouthwash and gargle for gingivitis and sore throats[, ]. The poultice has also been applied to the armpits to treat itchiness there[].

The inner bark is diaphoretic and styptic[, , ]. An infusion is used in the treatment of colds and abdominal pains[, , ].
A decoction of the inner bark has been applied externally in the treatment of eczema and other skin conditions[]. The pulverized inner bark has been applied to cuts and wounds to stop the bleeding[].

A tea made from the leafy twig tips is used in the treatment of dysentery, kidney ailments, colds and rheumatism[, , ].
Externally, the twigs are used in steam baths for treating colds, rheumatism and to induce sweating[]. A decoction of the branches has been boiled down to a syrup or thick paste and used as a poultice on arthritic joints[]. A poultice of the crushed branch tips has been used to treat infections on an infants navel[].

Hemlock pitch has been used externally as a counter-irritant in the treatment of rheumatism[].

Agroforestry Uses:

Tolerant of light trimming, plants can be grown as a hedge[]. This species does not make a good hedge in Britain[].
Some dwarf cultivars can be grown as a ground cover when planted about 1 metre apart each way[]. 'Pendula' is slow-growing but makes a very good cover[].

Other Uses

The tree yields a resin similar to Abies balsamea, it is gathered by incisions in the trunk or by boiling the wood[, , ].

A pitch (called hemlock pitch), is obtained by distillation of the young branches[]. 'Oil of Hemlock' is distilled from the young branches according to another report[].

The bark contains 8 - 14% tannin[, , ]. The inner bark is used according to one report[].

The inner bark has been used in making baskets[].

A red to brown dye is obtained from the bark[, , ]. A red dye is obtained from the inner bark according to another report[]. A little rock dust has been added to act as a mordant when boiling the bark[].

The boiled bark has been used to make a wash to clean rust off iron and steel, and to prevent further rusting[].

The wood is coarse-grained, light, soft, moderately strong, brittle, not durable outdoors[, , , , , , ]. It is difficult to work because it splits easily[]. The wood weighs 26lb per cubic foot[]. The trees do not self-prune and so the wood contains numerous remarkably hard knots that can quickly dull the blade of an axe[]. The wood of this species tends to be brittle and inferior to that of the other North American Tsuga species[]. A coarse lumber, it is used occasionally for the outside of buildings[, , , , , ]. The wood is of good quality suitable for use in construction for making roofs, floors etc., and for making crates or boxes, but until recently these kinds of use were completely overshadowed by its widespread use in the paper pulp industry[]. Other former uses were to make telegraph poles and railway sleepers[].
The wood is used as a fuel. It should be used with caution as a fuel for outdoor fires because it can project embers and burning wood several metres from the fire[].

Propagation

Seed - it germinates better if given a short cold stratification[, ] and so is best sown in a cold frame in autumn to late winter. It can also be sown in early spring, though it might not germinate until after the next winter. If there is sufficient seed, an outdoor sowing can be made in spring[]. Pot-grown seedlings are best potted up into individual pots once they are large enough to handle - grow them on in a cold frame and plant them out in early summer of the following year. Trees transplant well when they are up to 80cm tall, but they are best put in their final positions when they are about 30 - 45 cm or less tall, this is usually when they are about 5 - 8 years old[]. Larger trees will check badly and hardly put on any growth for several years. This also badly affects root development and wind resistance[].