Common name: Tea Tree

Tea Tree is an essential-oil-yielding shrub or small tree originating in Australia, with 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 up to 14 m (46 ft) tall, with a trunk 30 cm (1 ft) in diameter. However, it is typically 2 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 it is tall. The bark is papery, grey-white and peels in sheets that persist in layers on the trunk and branches.

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

In spring, spikes of fluffy, creamy-white flowers cover the crown, almost completely hiding the green foliage. Small, woody, cup-shaped seed capsules follow, closely spaced along the branchlets, becoming dry and light brown when mature, with many tiny seeds inside.

Material uses

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

Steam distillation extracts the oil, yielding 1 to 2% of the leaves by weight, depending on the variety, growing conditions, and the 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 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.

Natural fragrance - Tea tree oil also has potential uses in perfumery, agriculture,

Veterinary use - ...and veterinary medicine (e.g., controlling lice infestation in sheep).

Natural disinfectant - In hospitals, the oil has been shown to be effective against golden staphylococcus (Staphylococcus aureus).

Anti-mildew agent - A relatively recent application is controlling mould and bacteria in air-conditioning systems.

Health uses

Tea tree oil has natural antiseptic, antibacterial and antifungal properties. People generally apply it to insect bites, stings, wounds, burns, acne, warts, athlete's foot, vaginal yeast infections and other topical conditions. It is also used in inhalation treatments for coughs, colds, and flu.

Natural dental care - People also apply tea tree oil to oral infections, including gum disease.

Aromatherapy oil - Tea tree oil is also used in aromatherapy for general well-being.

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 impractical because of the small seed size, so growers sow seeds in containers in a free-draining potting mix. The emergent seedlings are then tended in a nursery until about 10 to 16 weeks old. They are then planted in rows on land that supports mechanical harvesting. Farmers harvest newly planted crops first at 18 to 24 months, then on a 9- to 12-month rotation cycle, depending on climate conditions. Fresh-leaf harvests average 12,000 kg per hectare per year. On steam distillation, they yield about 180 kgs of oil, the equivalent of 160 lbs per acre.

Performs best in 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 tolerates seasonal flooding, saturated soils, soil salt, and strong winds.

Problem features

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

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

• Brophy, J. J., Craven, L. A. & Doran, J. C. 2013, Melaleucas: their botany, essential oils and uses, Australian Centre for International Agricultural Research (ACIAR), Canberra

• 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