Common Name: American Arbor-Vitae

General Information

Thuja occidentalis is an evergreen tree with a conical crown; it usually grows up to 15 metres tall, exceptionally to 38 metres, though it is stunted or prostrate in harsh environments. The straight, cylindrical bole is up to 90cm in diameter (exceptionally to 180cm) and is sometimes divided into 2 - 3 secondary stems. The tree often reproduces by means of layering or by forming erect, rooted branches from fallen trunks[].
Thuja occidentalis is an important timber tree, the wood being used especially for applications requiring decay resistance. It also has a range of medicinal uses, was a traditional food of the native N. Americans and has a range of other uses. The tree is often grown as a timber crop in temperate regions, and is widely utilized as an ornamental - it has more than 120 named cultivars. It was probably the first North American tree introduced into Europe (ca 1566)[].
Thuja occidentalis is extremely widespread and in some parts of its range is increasing by invasion of abandoned farmland. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

The essential oil in this plant contains thujone. Thujone is a GABA receptor antagonist which allows neurons to fire more easily. In larger doses this can cause muscle spasms and convulsions, and can also be toxic to brain, kidney, and liver cells.
There has been a lot of negative press regarding thujone, particularly in the mid 19th century when thujone was reported to be more dangerous than alcohol - since shown to be exaggerated; and reports in the 1970’s that it might have a similar effect on the brain to THC (found in cannabis) – since found to be incorrect.
Thujone is probably best known for its use in the alcoholic drink ‘Absinthe’. It is also found in the essential oils of many other plants that are used in herbal medicines and foods, including Arborvitae (Thuja species), some Junipers (Juniperus species), Wormwoods (especially Artemisia absinthium) and Sage (Salvia officinalis). There are some legal restrictions in various countries on the quantity of thujone that can be added to foods and drinks and these vary between countries.
Side effects from consuming thujone can include sleeplessness and anxiety but, unless the pure essential oil is used, the quantity of thujone found in plants is well within safety levels. Pregnant women, however, may be advised to restrict their use of thujone-containing plants.

Botanical References

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Range

Central and eastern N. America - Manitoba to New Brunswick, south to Illinois, Tennessee and Virginia

Habitat

Swamps and cool rocky banks of streams[], forming dense almost impenetrable forests[, ]. On mostly calcareous substrates, neutral to basic swamps, shores of lakes and rivers, uplands, cliffs, and talus; at elevations up to 900 metres[].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	15.00 m
Growth Rate	Slow
Pollinators	Wind
Cultivation Status	Wild

Cultivation Details

Thuja occidentalis occupies a geographical range touching in the north on the subarctic taiga-tundra interface and in the south it extends well into the belt of deciduous angiosperm forests. It is a very hardy tree, tolerating very cold winters with temperatures down to -46°c[, ]. In cold weather the leaves turn brown, becoming green again in the spring[].
Prefers a permanently moist soil[], it is intolerant of dry soils[]. A useful plant for very poorly-drained soils[, ]. It grows equally well in swamps and on dry ground, but avoids extremes of both habitats; it is often growing abundantly on soils over limestone in upland areas and on alluvial soils with a high organic and mineral content in lowlands (rich fens supporting forest)[]. The best stands in America are on well-drained soils[]. Grows well in heavy clay soils. Succeeds in sandy soils[] and on chalk[].
It is usually a slow growing and short-lived tree in cultivation in Britain and rarely looks thrifty[, ]. However, there are some good specimens in western Britain[, ]. Some cultivars are more healthy, 'Lutea' is growing very well in several places and 'Spiralis' is also growing well[].
Trees live 200 - 300 years in the wild[].
The tree is sometimes planted for timber tree in central Europe[].
Plants cannot regenerate from old wood. Pruning is not normally necessary for this species, any pruning that is carried out should be done with care, not cutting back into old wood[].
The wood and the foliage are strongly aromatic[]. The crushed leaves have a scent of apples[].

Edible Uses

Pith of young shoots - cooked[]. It can be added to soups[]. Pleasantly sweet, the pith was used as the basis of the soup according to one report[].

Inner bark - cooked. It is only used in times of emergency or scarcity[]. The inner bark can be dried and ground into a powder, then used with wheat or other cereals in making bread, biscuits etc.

The leafy branchlets are used as a tea substitute[, , ] but are probably best avoided by pregnant women[]. An aromatic flavour[]. Another report says that the foliage and bark are used, the resulting tea is a good source of vitamin C[].

Medicinal

American arbor-vitae was much used by many native North American Indian tribes as a medicine to treat fevers, coughs, headaches, swollen hands and rheumatic problems[, ]. The plant has an established antiviral activity and is most commonly used in modern herbalism to treat warts and polyps, being prescribed both internally and externally for these conditions[]. The plant can be used to induce menstruation and so should not be prescribed for pregnant women[].

The recently dried leafy young twigs are alterative, anthelmintic, anti-inflammatory, antiseptic, aromatic, astringent, diaphoretic, diuretic and emmenagogue[, , , ]. The plant is being used internally in the treatment of cancer[], especially cancer of the uterus[]. A tea made from the leaves is used in the treatment for bronchitis and other respiratory problems, colds, headaches and as a cough syrup[, ]. The plants diuretic properties make it useful in treating acute cystitis and bed-wetting in children[].
The leaves are used in steam baths in the treatment of rheumatism, arthritis, colds etc[].
Externally, the leaves are used as a wash for swollen feet and burns[]. Extracts of the leaves can be painted on painful joints or muscles as a counter-irritant, improving local blood supply and thus facilitating the removal of toxins, easing pain and stiffness[]. A tincture of the leaves has been used in the treatment of warts, piles, bed sores and fungal infections[].
The leaves and young twigs can be harvested as required and used fresh or dried[].

'Oil of white cedar', obtained from the leaves, is an essential oil that is antiseptic, expectorant and rubefacient[, ]. It is used internally to promote menstruation and relieve rheumatism[]. This volatile oil is toxic and poisoning from overdoses has occurred[], it should only be used under the supervision of a qualified practitioner and should not be prescribed for pregnant women[]. The oil also stimulates the heart and causes convulsions in high doses[].

A tea of the inner bark is used to promote menstruation[] and in the treatment of consumption and coughs[].

A homeopathic remedy is made from the leaves and twigs, gathered when the tree is flowering[]. It is used in the household as a treatment against warts, but also has a range of other applications that should only be prescribed by a competent homeopath[, ].

Agroforestry Uses:

Tolerant of regular trimming, though not into the old wood, it can be grown as a hedge[].
A natural pioneer species, it invades abandoned fields and pastures. especially in the northeast of the United States[]. It can be used in reforestation programmes to restore native woodland[].

Other Uses

The fresh branches are used as besoms[]. Their aromatic smell serves to deodorize the house whilst sweeping[].

The leaves have been kept in the clothes cupboard as a perfume, incense and insect repellent[]. The leaves and stems have been used as an incense[].

An essential oil is obtained from the leaves and branches, it is used in perfumery and in medicines[, , , ]. It is poisonous if taken internally[]. This essential oil also has insect repellent properties[].

The tough and stringy bark has been used to weave fibre bags[].

The bark is a source of tannin[].

The wood is light, soft, not strong, brittle, coarse grained, very durable, easily worked, does not warp[, , , , ]. It weighs 20lb per cubic foot[]. It is used especially where contact with water cannot be avoided, for making items such as canoes, garden buildings, shingles, posts etc[, , , , ]. The rot resistant properties of the wood make it an excellent timber for outdoor uses. These include rustic fencing, garden gates and sheds, and shingles. Canoes are still made from this wood because of its light weight, as are tubs and barrels. More industrial uses are found in kraft pulp and particleboard[]

Propagation

Seed - best sown when ripe in the autumn in a cold frame[]. Stored seed germinates best if given a short cold stratification[]. It can be sown in a cold frame in late winter. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts.
If growing large quantities of plants, the seed can be sown in an outdoor seed bed in mid spring[]. Grow the plants on for two years and then plant them out into their permanent positions in late autumn or early spring.
Cuttings of half-ripe wood, 5 - 8cm with a heel, mid summer in a shaded frame. Forms roots by the end of September but it should be overwintered in a frame[].
Cuttings of almost ripe wood, 5 - 10cm with a heel, September in a cold frame. Forms roots in the following summer. Plant out in autumn or spring[].