Tree of the Week: Lemon-scented gum

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Lemon-scented gum -- Corymbia citriodora

Tall and towering, with a smooth, pinkish white, bare trunk extending for half its height and graceful open foliage borne in distinct layers, the lemon-scented gum stands out in the landscape. Most people would call this native from the central and northern coasts of Queensland, Australia, a eucalyptus but it was reclassified as a Corymbia.

Fast growing to 45 to 90 feet, this widely planted evergreen tree remains rather narrow at 20 to 40 feet. Eventually it produces a dense, sturdy wood, but initially it grows so fast that judicious cutting back is needed to strengthen the trunk. But since pruning practices too often leave a lot to be desired, here we still see many horizontal branches cut off which shouldn’t be, or indiscriminate heading back taking place. Powdery bark on the tree sheds in thin curling flakes. The tree is deep rooted and often planted closer than normal to walks and walls. The drooping, narrow, adult leaves are 3 to 7 inches long, yellowish green and smooth; the juvenile leaves look similar but have a more sandpapery feel. Crushing a leaf produces a strong lemon smell due to the presence of citronella and other essential oils. Winter and spring blooming white flowers are not very flashy; the urn shaped seed capsules are hard as wood. The tree takes a variety of soils, needs full sun and is medium drought-tolerant. But if its internal moisture content goes down too low the tree becomes quite susceptible to pests and diseases. Introduced tiny predatory wasps are gradually bringing the sometimes fatal attacks by aphid related psyllids under control; this biological control is far preferable over chemical sprays, which have undesirable consequences.

Unlike the strongly scented oil from the blue gum, Eucalyptus globulus, of vapor rub and lozenge fame, the more delicately scented oils from the lemon-scented gum are used for perfumes, antiseptics, insect repellents, medical applications and aromatherapy. The tree is grown in many subtropical countries for timber and firewood production.

-- Pieter Severynen

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