Common name: Narrow-leaved Peppermint

Narrow-leaved Peppermint is an essential-oil-yielding eucalyptus native to eastern Australia, with a natural range extending from near Melbourne in Victoria, through Ballarat and Gippsland, to the high country of New South Wales, as far north as the Queensland border.

On favourable forest sites, it may reach up to 50 m (164 ft), with a trunk diameter of 1.5 m (5 ft). However, it is typically around half that height, with a straight trunk supporting a moderately branched crown. On open sites, it is somewhat shorter and develops a large, rounded crown. The bark is grey or dark brown, smooth on young trees, and becomes vertically fissured, fibrous, and strappy with age.

Like other eucalyptus species, the leaves change shape as the tree matures. In this species, they change from pairs of stalkless, dull green, broadly lance-shaped leaves on young trees to alternately arranged, long-stalked, dull green, lance-shaped leaves on mature trees. They remain on the tree throughout the year and release a strongly menthol-like aroma when crushed.

The flowers are typical of a eucalypt, being perfect (bisexual) and small, with long, creamy-white filaments set in a cup-shaped base. They arise at the sides of the branches, usually in groups of eleven to twenty and bloom from spring through summer.

Fertilised flowers develop into small, goblet-shaped seed capsules that become dark brown and woody when they mature, with tiny, glossy brown, pyramidal-shaped seeds inside.

Maranoa Gardens, Melbourne, Australia

Material uses

Essential oil - Steam distillation of the leaves yields 3 to 5% eucalyptus oil of two distinct types, depending on the variety. The variety known as 'A' yields eucalyptus oil with a high cineole (aka. eucalyptol) content, the most valuable of the Eucalyptus oils due to its medicinal and antiseptic qualities. It is almost identical in composition to oil from Broad-leaved Peppermint (Eucalyptus dives), a closely related eucalyptus species that overlaps with it in its native distribution. When extracted, both 'A' and 'B' type oils are colourless but age to pale yellow, especially under long or poor storage conditions.

Stain removal - Cineole-type oils are also good stain removers, proven effective at removing grease, glue, and dried stains from skin and clothing.

Anti-mildew agent - Eucalyptus oils are also generally used for mould removal, 

Natural disinfectant - ...as a disinfecting agent,

Natural fragrance - ...and in perfumery. The variety known as 'B' produces an oil unsuitable for medicinal purposes, but it has a robust, peppery-camphoraceous aroma that makes it attractive to the fragrance industry.

Natural insecticide - It is also used in pest insect-control products.

A significant amount of 'B'-type oil is also produced and used in the mining industry to create froth to separate floating from non-floating minerals, and as a solvent or hardener in paints and lacquers.

Hardwood - The timber is moderately heavy, averaging 720 kg per cubic meter (45 lbs per cubic ft), and has light-brown heartwood. However, it shrinks significantly on seasoning and is not durable, with low natural resistance to rot, decay and wood-boring insects.

Timber and lumber - It is mainly used for indoor construction or other applications where a durable wood is not required.

Environmental uses

Public garden tree - Narrow-leaved Peppermint develops an attractive form on sites with adequate moisture and deep soil, with a straight trunk and large, densely leafy crown. In Australia, local town councils recommend planting it as an amenity tree in town parks and public gardens.

Health uses

Cineole-type eucalyptus oil is a proven expectorant and antiseptic, particularly against Streptococcus. It is used in cough drops, syrups, and vaporiser fluids, and in ointments, liniments, and gargles for its general antiseptic action.

Natural dental care - It is also used in oral hygiene products such as toothpaste and mouthwash, and commonly in dentistry as a solvent and sealer for tooth fillings after root canal surgery.

Climate

Narrow-leaved Peppermint grows naturally in humid subtropical and warm-temperate climates, generally areas with annual lows of 5 to 12°C, annual highs of 16 to 25°C, annual rainfall of 600 to 1400 mm and a summer or winter dry season of 5 months or less.

Growing

New plants are mostly grown from seed, which germinate readily. The seeds are sown in containers with a free-draining potting mix and usually germinate within two to five weeks. Seedlings are then tended in a nursery until around 30 to 50 cm tall, then planted out.

Narrow-leaved Peppermint performs best on free-draining clay-loam, loam, sandy-loam and loamy-sand soils of a moderately acid to slightly alkaline nature, generally with a pH of 5.0 to 7.5, and on sites with full to partial sun exposure. It has poor tolerance to waterlogged or poorly drained soils.

Problem features

None known

Books

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

• Boland D.J., Brophy J.J. & House A. P. N. 1991, Eucalyptus leaf oils, use, chemistry, distillation and marketing, Australian Centre for International Agricultural Research (ACIAR) & Commonwealth Scientific Industrial Research(CSIRO), Inkata Press, Melbourne

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

• Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

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

• F. R. Beuhne 1922, Honey flora of Victoria, Melbourne Albert J. Mullett, Govt. printer

• Jacobs M. R. 1979, Eucalypts for planting, Food and Agriculture Organization of the United Nations (FAO), Rome

• Nicolle, D. (2016). Taller Eucalypts for Planting in Australia: Their Selection, Cultivation and Management. Dr Dean Nicolle, Adelaide.

• Scheffer, T. C & Morrell, J. J. 1998, Natural durability of wood : a worldwide checklist of species, Forest Research Laboratory, Oregon State University, Corvallis, Oregon

• Streets, R. J. & Troup, R. S. 1962, Exotic forest trees in the British Commonwealth, Oxford University Press, Oxford, England

Articles, Journals, Reports and Working Papers

• Ciesla W.M. 2002, Non-wood forest products from temperate broad-leaved trees, FAO Technical Papers 15, Food and Agriculture Organization of the United Nations (FAO), Rome