Eucalyptus (Gum tree - Myrtaceae) is a genus of evergreen trees and shrubs containing over 600 species, varieties and hybrids from Australia and Tasmania. Of all plant genera, this genus shows the greatest variation in size at maturity, ranging from small shrubs of under 3 metres to the tallest known broadleaf tree in the world (Eucalyptus regans, 124m). There are species adapted to almost every climatic condition from freezing alpine regions to arid desert to tropical rainforest.
The hardy Eucalypts grow well in gardens as trees, pruned shrubs and stooled plants. Less hardy species are good in bedding schemes, or as foliage pot plants in sheltered areas or conservatories.
Prolific flowering begins in hardy species when they are from 4 to 6 years old. The flower buds occur in umbels from the leaf axils in early summer and open a year later into tufts of stamens with cream-coloured or white flowers. The individual flowers are 1 to 2.5cm across and are sweet scented.
Most Eucalypts require full sun and well drained soil of moderate fertility which must be kept moist in the summer until the plants are established. Eucalypts will thrive on both acid and slightly alkaline soils from pH 4.5 to 7.5. Plant from May to September ideally and avoid root restriction as Eucalypts are sensitive to root damage. Many species are fast growers and some may grow at a rate of 1 to 2.5 metres per year. In exposed sites young plants should be staked for the first two years to prevent wind rocking. Protection of the basal stem is advisable for the more tender species in the first winter in colder areas.
With regard to pests and diseases the Eucalypts are generally trouble free. However, the species of psyllid (Ctenaryaina eucalypti) can be a problem with the more glaucous species at the juvenile leaf stage. The snow gums are not affected by this pest. Silver leaf disease (Stereum purpureum) and aphids (Aphididae) can occasionally be a problem.