Thuja occidentalis, Arbor vitae

An evergreen conifer from North America with aromatic foliage, traditionally prized for ­purification and having antiseptic and antiviral properties.

scientific name Thuja occidentalis L.

family Cupressaceae

alternate names American white cedar, tree of life

parts used Leafy twigs

Description

Arbor vitae is an evergreen tree growing to 15m tall by 5m wide, possibly taller in damp nutrient-rich soils. It is monoecious with male and female flowers growing on the same plant and is wind pollinated. It has flat scale-like leaves and small cones. On older trees the bark sheds in long ragged strips.

Habitat

Indigenous to eastern North America, growing in moist and rocky soils. It is widely cultivated as an ornamental or hedging plant.

Related plants

Western red cedar (T. plicata) is used to produce an essential oil for insect repellent and topical cosmetic uses.1 There are ornamental arbor vitae varieties, including ‘Smaragd’ or ‘Emerald Green’, a semi-dwarf compact shrub to 4m spreading to 1m. An Asian species of the cypress family, Platycladus orientalis (previously known as T. orientalis), is used in traditional Chinese medicine.

Arbor vitae trees at Weleda, Nottinghamshire, UK

Cultivation and harvest

Cultivation

Arbor vitae is hardy to USDA zones 3 (UK zone 2) and will grow in full sun to part shade. It can be grown on most soils, and grows best in moist well-drained soils. Arbor vitae can be used to form a hedge as it is tolerant of regular trimming. Whole branches can be harvested close to the main stem.

Pests and diseases

The young leaves are eaten by deer.

Propagation

Fresh ripe seed is sown in the autumn in a cold frame. Stored seed germinates best if given a short period of cold stratification. 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 out into their permanent positions in late spring or early summer, after the last frosts. Cuttings of half-ripe wood, 5-8cm with a heel, can be taken in July/August in a shaded frame, and overwintered in a frame. Cuttings of almost ripe wood, 5-10cm with a heel in September.

Harvesting

The leafy young twigs can be harvested in spring and used fresh in infusion or dried for later use. An essential oil can be distilled from the leafy twigs.

The leaf of arbor vitae

Therapeutic use

Traditional

Traditionally, arbor vitae was considered purifying and used by Native Americans for colds, fever, cough, headache, skin disorders, swollen extremities and rheumatic problems.2

Medicinal actions and uses

Antimicrobial, antiviral, anti-inflammatory, diaphoretic, diuretic, emmenagogue, immunostimulant and laxative. The essential oil is antiseptic, expectorant and rubefacient.

A tea of the leaves has been used internally for respiratory problems, and externally as a wash for swollen feet or burns. The tincture has been used to treat fungal skin infections and warts. The powdered leaves can be used as an insect repellent.

Clinical applications and research

Limited studies have been carried out. Arbor vitae is part of a herbal product, Esberitox, used in viral upper respiratory tract infection, supported by randomised controlled trials for reducing common cold symptoms.3 Thujone, a toxic constituent of the essential oil, has been investigated for possibilities of use against brain tumour cells.4

Preparations and dosage

The leaf can be infused in oil for external use in skin complaints such as warts. Arbor vitae leaf tincture, which is high in alcohol (90%), contains significant amounts of thujone, and is only for external use. A tincture with a lower proportion of alcohol (30%) is safer for internal use, 1-2ml three times per day.5

Constituents and commerce

Key constituents

Fresh leaves contain essential oils (1-4%), sugars, poly­saccharides, minerals and are high in vitamin C. The essential oil contains monoterpenes including thujone, isothujone, fenchone, sabines and pinenes.

Commerce

Esberitox is promoted for the common cold and contains arbor vitae, purple coneflower (Echinacea purpurea and E. pallida) and wild indigo root (Baptisia tinctoria) extracts.

Safety

Not for use in pregnancy. Not for long-term use. Large doses of fresh arbor vitae leaves and twigs are irritant to the gastrointestinal tract, uterus, liver and kidney. The essential oil is not for internal use.

Other uses

Shelter belt formation and hedging. Incense smudge sticks. Disinfectant and moth repellent. Floristry wreaths. Timber.

1 Han X and Parker TL. (2017) Arborvitae (Thuja plicata) essential oil significantly inhibited critical inflammation- and tissue remodeling-related proteins and genes in human dermal fibroblasts. Biochim Open 20: 56-60.

2 Duke JA. (1983) Handbook of energy crops, unpublished text from https://hort.purdue.edu/newcrop/duke_energy/Thuja_occidentalis.html (accessed 26 August 2018).

3 Naser B, Bodinet C, Tegtmeier M, et al. (2005) Thuja occidentalis (Arbor vitae): A review of its pharmaceutical, pharmacological and clinical properties. Evid Based Complement Alternat Med 2: 69-78; Henneicke-von Zepelin H, Nicken P, Naser B, et al. (2019) Non-interventional observational study broadens positive benefit-risk assessment of an immunomodulating herbal remedy in the common cold. Curr Med Res Opin. 35: 1711-1719.

4 Pudełek M, Catapano J, Kochanowski P, et al. (2019) Therapeutic potential of monoterpene α-thujone, the main compound of Thuja occidentalis L. essential oil, against malignant glioblastoma multiforme cells in vitro. Fitoterapia 134: 172-181.

5 Mills and Bone (2005) pp600-601.