Common name: Tea Tree

Tea tree is an essential-oil yielding shrub or small tree originating in Australia, its natural range extending over a small area from near Port Macquarie in northern New South Wales to Stanthorpe in southeast Queensland. As with other members of the paper-bark-tea-tree family, it thrives on swampy, poorly drained sites or sites subject to flooding or that turn into watercourses during the rainy season. 

It may reach heights of up to 14 m (46 ft), with a trunk 30 cm's (1 ft) in diameter. However, it is more typically2 to 3 m (7 to 10 ft) tall and shrub-like, with multiple trunks supporting a densely leafy, wide-spreading crown, often as wide as the plant is tall. The bark is papery, grey-white and peels in sheets that persist in layers on the trunk and branches.

The leaves are lance-shaped and small, under 1 cm (0.4 in) in length, bright green and closely arranged in whorls along thin branchlets, themselves packed tightly in the crown, casting a deep shade on the ground below. They remain on the plant throughout the year and, when crushed, release a camphorous aroma.

In spring, spikes of fluffy, creamy-white flowers cover the crown, almost completely hiding the green foliage from view. They are followed by small, woody, cup-shaped seed capsules closely spaced along the branchlets, becoming dry and light brown when mature with many tiny seed inside.

Use

The leaves are the principal source of 'Tea tree oil', one of only two species officially recognised by the International Organization for Standardization (ISO) as the source of Tea Tree oil. The other is Snow-in-summer (Melaleuca linariifolia), a minor source.

The oil is extracted by steam distillation, giving yields that range from 1 to 2% of the leaves by weight, depending on the variety, growing conditions and proportion of old- to new-growth in the distilled material. Tea tree oil is a colourless to pale yellowish-green liquid with a warm, spicy aroma, reminiscent of nutmeg, cardamom and sweet marjoram. It is used medicinally, mainly as an antiseptic, antibacterial and antifungal agent.  

Tea tree oil also has potential use in perfumery, agriculture and veterinary medicine (e.g. control of lice infestation in sheep). In hospitals, it has shown to be effective against golden staphylococcus Staphyloccocus aureus). A relatively recent application is its use in controlling mould and bacteria in air-conditioning systems.

It blends well with Clove oil (from Syzygium aromaticum), Cananga oil (from Cananga odorata), Lavender oil (from Lavandula angustifolia) and Rosemary oil (from Salvia rosmarinus), and has been used as an adulterant for Nutmeg oil (from Myristica fragrans).

Tea tree oil should be stored in a cool, dark, dry, air-free environment to minimise oxidation.

Health use

Tea tree oil has natural antiseptic, antibacterial and antifungal properties. It is generally applied to insect bites, stings, wounds, burns, acne, warts, athlete's foot, vaginal yeast infections, and oral infections, including gum disease and other topical afflictions. It is also used in inhalation treatments against coughs, colds, and flu and aromatherapy for general well-being.

Tea tree oil is found in various personal health care products, including gels, creams, lotions, shampoo, soaps, toothpaste, foot care products, insect repellents and air fresheners.

Climate

Grows naturally in humid subtropical and tropical climates, generally frost-free areas with annual lows of 9 to 21°C, annual highs of 22 to 35°C, annual rainfall of 800 to 1600 mm and a dry season of 3 months or less, extending to 7 months with irrigation or groundwater.

Growing

In commercial operations, new plants are started from the seed or cuttings of varieties known to be high-oil-yielding and rich in terpinen-4-ol (the active ingredient in Tea tree oil). It has to constitute 30 to 48% of the oil to qualify as Tea tree oil.

Direct sowing is not practical because of the small seed size, so seed are sown in containers in a free-draining potting mix. The emergent seedlings are then tended in a nursery until about 10 to 16 weeks old. Then they are planted in rows on land that facilitates mechanical harvesting. Newly planted crops are harvested first at 18 to 24 months and then on a 9 to 12-month rotation cycle, depending on the climate conditions. Harvests of fresh leaves average 12,000 kgs per hectare per year. On steam distillation, they yield about 180 kgs of oil, the equivalent of 160 lbs per acre.

Performs best on free- to slow-draining clay-loam, loam, sandy-loam and loamy-sand soils of an acid to neutral nature, generally with a pH of 4.5 to 7.0 and on sites with full to partial sun exposure. It has good tolerance to seasonal flooding, saturated soils, soil salt and strong wind conditions.

Problem features

Tea tree is assessed as a high weed risk species for Hawaii and Florida, respectively, by the Hawaii Pacific Weed Risk Assessment project (HPWRA) and the IFAS Assessment of Non-Native Plants in Florida's Natural Areas.

Books

• Arctander, S. 1960, Perfume and flavor materials of natural origin, Elizabeth, New Jersey

• Boland, D. & Brooker, I. & McDonald, M. W. 2006, Forest trees of Australia, 5th ed., CSIRO Publishing (Ensis), Melbourne

• Byrne, T. & Bourke, M. & Salvin, S. 2004, The new crop industries handbook, Rural Industries Research and Development Corporation (RIRDC), Canberra, Australia

• Chevallier, A. 2000, Encyclopedia of herbal medicine, 2nd American ed., Dorling Kindersley, New York

• Cribb, A. B. & Cribb, J. W. 1982, Useful wild plants in Australia, William Collins, Sydney

• Marcar, N. E. 1995, Trees for saltland : a guide to selecting native species for Australia, Division of Forestry, Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia, Canberra

• Oyen, L. P. A. & Nguyen X. D. 1999, Plant Resources of South-East Asia (PROSEA) 19 : Essential-oil plants, Backhuys Publishers, Leiden

• Singh, D. ed., 2014. Advances in plant biopesticides, Springer Publishing, New Delhi, India

• Winter, R. 2009, A consumer's dictionary of cosmetic ingredients : complete information about the harmful and desirable ingredients found in cosmetics and cosmeceuticals, 7th ed, Three Rivers Press, New York