Common name: Grey ironbark

Grey ironbark is an Australian eucalypt valued for its timber and the honey produced from its flowers.

Also included in this description is the closely related but botanically separate Eucalyptus drepanophylla, also known as Grey Ironbark. As it differs only marginally from Eucalyptus paniculata, mainly in its distribution.

Its natural range is limited to Eastern Australia, to the coastal strip extending from Bega, in New South Wales, to Bundaberg in South East Queensland and hilly areas in the continent's tropical north.

It can grow to become a large tree up to 30 m (100 ft) in height with a trunk diameter of 1.5 m (5 ft), though it is more typically 18 to 25 m (60 to 82 ft) tall. The trunk is usually straight, clear of branches for up to two-thirds the tree's height and supports a moderately leafy crown, compact in young trees, with age becoming broader and more open. The bark is light to dark grey, thick, hard and deeply furrowed.

As with many eucalypts, the leaves change shape as the tree matures. The leaves on seedlings and juveniles are ovate or broadly lance-shaped and short, those on fully-grown trees narrowly lance-shaped and up to 15 cm (6 in) long. Dark, dull green on top and slightly paler underneath, they remain on the tree throughout the year.

The flowers are typical of eucalypts, with long white filaments arising from a small goblet-shaped base. They bloom from autumn to spring, extending into summer in some areas, in clusters of up to nine at the ends of the branches.

Fertilised flowers are followed by small, green, cone-shaped seed capsules up to 1 cm (0.4 in) long, becoming brown and woody when mature with small, brown, ovoid seed inside.

Use

Grey ironbark is a major honey tree in its native Australia and countries where it is introduced, including Kenya and South Africa. Nectar flows peak every three years and in the first four to six weeks of flowering, with hefty flows after rains following a dry period.

Yields are in the range of 50 to 100 kgs (110 to 220 lbs) of honey per colony per season. The honey is extra light-amber to a pale-straw colour, sweet with a warm, subtle, fresh buttery taste, dense texture and granulates slowly to a fine to medium grain.

The wood has dark brown or red-brown heartwood, is very strong, hard and heavy, in the 1000 to 1100 kg per cubic meter (62 to 69 lbs per cubic foot) range, and has high natural resistance to rot, decay and wood-boring insect. This classes it as a durable hardwood, suitable for both indoor and outdoor construction.

Suitable logs are sawn into beams and planks used in heavy construction, including bridge and wharf construction, boat-building, house construction, as well as for poles and posts, railway sleepers, and heavy-duty flooring, decking and outdoor furniture. It is also an excellent fuelwood, suitable for firewood and for making high-quality charcoal.

Climate

Grows naturally in humid subtropical and tropical mid-elevation climates, generally areas with annual lows of 9 to 20°C, annual highs of 20 to 27°C, annual rainfall of 700 to 2000 mm and a dry season of 7 months or less.

Trees introduced into Hawaii, on the islands of Maui and O'ahu, thrive in forest plantations at elevations of 300 to 1000 meters (1000 to 3300 ft).

Growing

New plants are usually started from seed, which remain viable for several years stored under cold, dry, air-tight conditions. The seed are sown in containers with a free-draining potting mix, and most germinate within seven to ten days. Seedlings are cared for in a nursery for around six to eight months, after which they are ready for planting out.

Performs best on free-draining clay-loam, loam and sandy-loam soils of a moderately acid to neutral nature, generally with a pH of 6.0 to 7.5 and on sites with full sun exposure.

Problem features

Grey ironbark is classed as a Category 2 (or significant weed) in South Africa, where it has become an invader of watercourses. It is assessed as a high weed risk species for Hawaii and Florida, respectively, by the Hawaii Pacific Weed Risk Assessment (HPWRA) project and the IFAS Assessment of Non-Native Plants in Florida's Natural Areas.

Books

• Blake, S. T. & Roff, C. 1987, The honey flora of Queensland, 3rd ed., Queensland Department of Primary Industries (QLD DPI), Brisbane

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

• C.A.B. International 2013, The CABI encyclopedia of forest trees, CABI Publishing, Wallingford, Oxfordshire

• Crane, E., Walker, P. & Day, R. 1984, Directory of important world honey sources, International Bee Research Association, London

• Doran, J. C & Turnbull, J. W. 1997, Australian trees and shrubs : species for land rehabilitation and farm planting in the tropics, 2nd ed, Australian Centre for International Agricultural Research (ACIAR), Canberra, Australian Capital Territory

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

• Little, E. L. & Skolmen, R. G. 1989, Common forest trees of Hawaii (native and introduced), Agricultuural Handbook No. 679, Forest Service, U.S. Department of Agriculture, Washington, D.C.

• Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

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

• Troup, R.S. & Joshi, H. B. 1975 to 1981, Silviculture of Indian Trees (3 volumes), Government of India Publications, New Delhi

• Webb, D. B. 1984, A Guide to species selection for tropical and sub-tropical plantations, 2nd ed., Unit of Tropical Silviculture, Commonwealth Forestry Institute, University of Oxford, Oxfordshire