Leptospermum and its Relatives - Cultivation

Introduction

With such a large and diverse group of plants which inhabit most climatic niches, it is not possible to give more than a brief and fairly superficial guide to some of the more commonly seen genera and species. The wide distribution of the Leptospermum Alliance also means that problems may be experienced when trying to grow a species in a different climate to that of its natural habitat. As a general guide:

• Species native to south western Australia when dry summers and wet winters are experienced may prove unreliable in tropical and sub tropical areas and temperate areas of wet, humid summers.
• Tropical species may be difficult to maintain in cold districts.

Despite these cautions, a number of species have proven to be adaptable in seemingly unsuitable climates. For example, the western species M.fulgens, M.nesophila, M.lateritia, M.diosmifolia and M.huegelii are grown very successfully in coastal areas of New South Wales and Queensland while the tropical species M.viridiflora will grow successfully in colder districts if it is protected from frost when young. The two western Callistemon species are also successful in many east coast areas and even spectacular western Kunzea such as K.baxteri and K.pulchella can be grown successfully in the south-east. However, when selecting plants for the garden it is always worth considering the natural distribution of the species and, if in doubt about the suitability of the plant, seek advice from local specialist nurseries.

Some of the plants in the Leptospermum Alliance, particularly Melaleuca and Callistemon, can be found in nature in poorly drained areas. A few, including Melaleuca quinquenervia and M.linariifolia are found in locations where their roots are either permanently or seasonally subject to innundation. As a general rule, however, most plants in this group will perform best in medium to light soils (eg. sandy loam) that are well drained but which retain some moisture. Most require a sunny or lightly shaded position for best flowering.

Left: Members of the Leptospermum Alliance usually respond well to severe pruning. Right: Sawfly larvae on the foliage of Callistemon citrinus. Photos: Brian Walters

Most species respond favourably to a light annual trim to promote bushy growth and the more robust growers will even respond to severe pruning if absolutely necessary. However, pruning those species which have a weeping growth habit can destroy their shape (eg.C.viminalis and its cultivars such as "Hannah Ray" and "Dawson River").

There are few pests that cause serious problems with this group of plants except that western species may be sensitive to root rot fungus (Phytophora sp.), which is one reason why they can be difficult to grow under humid summer conditions.

Other pests that can be troublesome are:

• Sawfly larvae. These are common pests of Callistemon. They are bronzy green in colour with a pointed tail and, because they occur in groups, they can inflict a great deal of damage to the foliage quickly. They are best controlled by physically removing them either by hand (using gloves!) or with a jet of water from a hose.
  
• Scale: This can attack a wide variety of native and exotic plants. On smaller plants it can be removed by a strong jet of water but this may need to be carried out several times. If this is not successful, and on larger plants, the traditional treatment with white oil is usually effective.
• Webbing caterpillar. These grubs commonly attack genera such as Melaleuca and Leptospermum but can cause damage to certain callistemons (the cultivar C."Little John" seems particularly prone). The insects cause branches to become bare of leaves and encrusted with a webbing material full of brown dust-like material. Again, a jet of water is effective treatment. The use of general insecticides is possible if effective contact with the caterpillars can be achieved but this is often difficult. Webbing caterpillar attack is most severe with fine leafed species.
  
  For further information on webbing caterpillar, see the article Teatree Web Moth (Webbing Caterpillar)

Right: Scale insects. Right: Webbing Caterpillar. Photos: Brian Walters and Ben Walcott

Species in the Leptospermum Alliance are fairly tolerant of fertilisers, unlike some other genera of Australian plants. The use of a slow release fertiliser after flowering will usually be sufficient.