Growing the Cooktown Orchid

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Dendrobium phalaenopsis
Cooktown Orchid (Floral Emblem of Queensland)
Family Orchid

The generic name Dendrobium is derived from the Greek 'dendron', meaning 'tree', and 'bios', meaning 'life'; plants of many species of this genus perch on tree trunks and branches. The specific name phalaenopsis from the Greek 'phalaina', meaning 'moth', due to the flower's resemblance to a moth. Dendrobium is a very large genus of more than 1400 species in south and east Asia and in the south-west Pacific. Dendrobium belongs to the orchid family, the largest family of flowering plants. This family is distributed widely throughout the world, with the greatest number in tropical areas. The common name, Cooktown Orchid, refers to the northern Queensland town, Cooktown, which lies within the distribution of the species on the Endeavour River, named by Captain Cook after his ship was repaired there in 1770.

Plants are up to 80 cm in height, comprising 3-20 flowering canes up to 1.5 cm in diameter. Three to six lance-shaped leaves, 5-12 cm long, are arranged on the upper parts of the pseudobulbs. The stems bearing the flowers are 10 to 40 cm long, carrying up to 20 flowers. Each flower is about 3 to 6 cm wide and usually coloured deep to pale lilac, or rarely white. It usually flowers in the dry season in the wild, but may flower throughout the year in cultivation.

Dendrobium phalaenopsis distribution map

It occurs naturally in northern Queensland, from Johnston River to Iron Range. Although it is found in tropical districts with very high summer rainfall, it is not a rainforest species but grows in exposed situations, usually attached to tree trunks such as paperbark melaleucas in savanah woodland or in vine thickets. Habitat alteration and indiscriminate harvesting by some commercial plant collectors have made this species rare or extinct in some places within its range, especially in the southern part.

Cooktown Orchids may be propagated from seed by commercial orchid laboratories, or mature plants may be divided at any time. As far south as Brisbane it is suitable for outdoor cultivation attached by wire or twine to the sunny eastern or northern side of a tree with persistent bark. Until the roots become fully established on the bark surface, they should be protected by a piece of hessian to avoid drying. A slab of cork provides a satisfactory alternative to cultivation on living bark. It may also be grown in pots or baskets, using fern fibre as a growing medium over a deep layer of broken crocks to provide effective drainage. South of Brisbane, glasshouse cultivation is necessary using pots or cork slabs. Generous watering must be provided during summer when growth is active. Winter watering is required only to avoid shrivelling, otherwise the plant is liable to decay and leaf-drop. Light applications of organic or artificial fertiliser during summer improve the number and size of flowers.

It is an ideal cut flower in autumn and winter, lasting up to two weeks in water, especially if pollination has not occurred. Flower-spikes can last up to three months, giving the species considerable commercial potential as an indoor flowering plant suitable for warm well lit rooms. Variations in the size and colour of flowers and the size of pseudobulbs have been noted. Several varieties have been described but these represent the extremes of a continuously varying range of shapes and colours of the flowers.

Cooktown Orchid is considered one of Australia's showiest orchid species and has been successfully cultivated in heated glasshouses in England since the latter part of the nineteenth century. In recent years they have been exported from Australia to New Zealand, USA, Papua New Guinea and Fiji.