Backhousia citriodora

Common name: Lemon myrtle

Other common names: Australian lemon myrtle, Lemon ironwood, Sweet verbena tree

Description

Lemon Myrtle is a flowering and essential oil yielding tree originating in Australia, its natural range limited to pockets of subtropical forest on the east coast of the continent.

Its growth is slow to moderate, to heights of up to 25 m (65 ft) in native forests with a slim, straight trunk up to 0.25 m (10 in) in diameter that is branch-free for more than half its height. On open sites, it is more typically 5 to 10 m (15 to 30 ft) tall with a low-branching habit, forming a densely leafy pyramidal crown. The bark is thin, grey- or light-brown, rough and fissured, sometimes flaking.

The leaves are lance-shaped, 7 to 12 cm (2.8 to 4.7 in) long, lime green when young, becoming dark green and have a strong lemon fragrance when crushed. They remain on the tree throughout the year.

From spring to early summer, small creamy-white flowers with long stamens bloom in profuse clusters that almost hide the green foliage from view. They are followed by brown, woody seed capsules with small seed inside. The seed are released when the capsules fall to the ground and split open on impact.

Use

The leaves on steam distillation yield a pale yellow, lemon-lime scented essential oil. The oil is used as a flavour and fragrance component and as a disinfecting agent in a wide range of industries, with use in food, perfumery, pharmaceutical, cleaning and toiletry goods. It has one of the highest levels of citronella found in any essential oil, which also gives it insect repellent properties, and its antimicrobial and antifungal properties have generated interest in its use as a natural food preservative. Corrosive to plastic, it must be stored and transported in glass or stainless steel containers.

Around 8,000 kgs of fresh leaves are harvested per hectare per year in commercial plantations and with an oil content of 0.7% to 1% yield 56 to 80 kgs of oil, or the equivalent of 50 to 70 pounds of oil per acre.

The fresh or dried and crushed leaves are used as a culinary herb, to add flavour to both sweet and savoury dishes, as well to flavour oils, syrups and preserves, or they can be brewed into a citrus flavoured tea.

The wood is heavy, averaging out at about 960 kgs per cubic meter (60 lbs per cubic ft) and the heartwood pale pink- to red-brown, but the logs come in diameters too small for sawing into lumber. The roundwood when available is used for turnery, tool handles and woodcraft more generally. Its natural durability to rot and decay, and wood-boring insects is not well researched.

The plant's low-branching habit lends itself to being grown as a fragrant hedge or privacy screen with pruning needed to keep it to a desired height and shape.

Climate

Grows naturally in moderately humid subtropical and tropical mid-elevation climates, generally best in frost-free areas with average annual lows of 10 to 19 °C, average annual highs of 20 to 30 °C, annual rainfall of 900 to 2000 mm and a dry season of 4 months or less.

Growing

New plants are usually started from semi-hardwood cuttings. It performs best on rich, moist, free-draining soil of a mildly acid to neutral nature, generally with a pH of 5.5 to 7.0 and on sites in partial sun exposure. It has poor tolerance to alkaline, slow-draining or waterlogged soils.

Problem features

There does not appear to be any record of it as a weed or as having naturalised anywhere in the world.

Where it grows

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