Eucalyptus johnstonii

Eucalyptus johnstonii lives up to its name of Tasmanian Yellow Gum with its predominantly yellow, but also orange-brown or pale green, smooth bark. Its mountain origins give it vigour and robustness, but also an excellent ability to resist cold, going down to -15 °C. This beautiful evergreen tree, with fairly rapid growth, quickly takes on the posture of a fine specimen, requiring little and attractive all year round. In the garden, it requires a suitable location, in full sun, in acidic or neutral, moist, well-drained soil, not too dry in summer. The young, very colourful and aromatic foliage, is very popular in floral composition.

Eucalyptus johnstonii is an endemic species of south-east Tasmania, on Mount Wellington, Bruny Island, Tasman Peninsula. In these high regions, at an altitude of 500 to 1000 metres (1640 feet 5 inches to 3280 feet 10 inches), in the high forests of the mountains and on the high plateaus, it develops on peaty and sandy soils, poorly drained, temporarily flooded, exposed to quite harsh climatic conditions (rain, winds, frosts). Belonging to the Myrtaceae family, it is commonly called Tasmanian Yellow Gum. It was described in 1922 by Joseph Maiden (1859-1925), a British botanist and the name johnstonii, honours the passionate geologist and botanist, Robert MacKenzie Johnston (1845-1918).

This eucalyptus forms a tree, with an erect habit, with a straight trunk, but dwarfed and stunted at high altitude, bearing numerous branches with flexible and pendulous shoots. In its natural habitat, it reaches a height of 40 to 50 m (131 ft 2 in to 164 ft) and 10 to 20 m (32 ft 10 in to 65 ft 7 in) in spread. In our climates, its more moderate size hardly exceeds 20 m (65 ft 7 in) in height. With fairly rapid growth, it rises on one or several trunks starting from a lignotuber* located just below the soil surface. When young, it displays brown to reddish shoots, bearing juvenile foliage, composed of ovate leaves 3 to 6 cm (1.2 to 2.4 in) long by 2 to 4 cm (0.8 to 1.6 in) wide, and shiny green. Then as it develops, the leaves take on a lanceolate to crescent shape, 7 to 15 cm (2.8 to 5.9 in) long by 2 to 4 cm (0.8 to 1.6 in) wide, shiny green. The leaves are tough, slightly aromatic and release a menthol scent when crushed, rich in eucalyptol. As it ages, the bark peels off in thin flakes, revealing a smooth underlayer, yellow to brownish or greenish. Flowering occurs from February to April in our climates, on plants a few years old. The inflorescence, arranged in the leaf axil, is composed of three small white flowers gathered in a tight bouquet, delicately scented and very attractive to bees.  After flowering, the fruits, called "gumnut", appear in the form of a woody capsule, globular, truncate, attached to the branch by a short petiole. They are a beautiful whitish-grey colour and remain attached to the stem for a long time. 

This eucalyptus has a *lignotuber, constituted by a swelling rich in starch that forms on the roots just below the soil surface. This organ allows it to grow again from the stump in the event of severe frost, fire or pruning to the ground. The plant also produces numerous shoots from dormant buds located under its bark, which allows it to respond well to cutting back, topping or more severe pruning.

The Tasmanian Yellow Gum finds a place in the garden planted alone in a clear space to appreciate the beauty of its bark and the elegance of its foliage. In order to highlight its architectural habit, it is trained on one or several trunks. It tolerates both semi-mountain and semi-arid climates in summer, and its resistance to cold will go down to -15°C. Note that this Eucalyptus, native to the high plateaus and alpine regions of Tasmania, tolerates peaty and sandy soils, even regularly waterlogged. It is therefore comfortable in moist, but not swampy soils, which it has the ability to dry out.