Cultivation of Leptospermum
Most members of the genus make useful ornamentals and some are fine specimen plants with attractive foliage or bark as well as showy flowers. L. scoparium, a species that Tasmania shares with New Zealand, has produced many cultivars. These have usually arisen as chance seedlings from New Zealand stock and will not be dealt with in this treatment.
Some have originated in other countries such as the United States, the United Kingdom and Ireland. The potential for further breeding with other species such as L. sericeum, L. rotundifolium, L. spectabile and L. macrocarpum is excellent and would undoubtedly produce cultivars far superior than have yet been seen.
Most tea-trees have showy flowers, often quite large and varying in colour from white, through pinks to red. Those with peeling bark reveal trunks in shades of shiny browns, greys or even pinks. Two species have highly aromatic, lemon-scented foliage, L. petersonii and L. liversidgei and others have pendulous branches which make them fine specimens.
Cultivation presents few problems as most adapt well to a variety of soil types. Full sun is preferred but many species will tolerate poor drainage and, in fact, some thrive in regularly inundated conditions. Tip pruning after flowering improves the vigour of most species and tends to avoid the woody appearance that may develop in some.
Propagation is easy from both seed and cuttings and cultivars must be reproduced by vegetative means if clonal properties are to be retained.
Pests and diseases
Unfortunately, a large number of species are prone to a variety of pests. Probably the worst and most common is the webbing caterpillar, which feeds on the foliage of most of the smaller-leaf species, matting the leaves together with webbing and filling it with their droppings. This can cause complete defoliation in small plants and may even cause death. The easiest and safest means of control, if the problem is found early enough, is to remove the mass of grubs, webbing and frass with the fingers and squash it. If spraying is considered necessary, a systemic spray must be used, as contact sprays are mostly ineffective.
Another prevalent pest is scale, which is usually associated with black smut causing an unsightly blackening of the foliage. The L. scoparium cultivars are particularly affected. Treatment is to spray with white oil when the crawling stage of the insect is mobile, usually in early spring. Later application should have an insecticide added to the white oil solution, to obtain effective control.
Borers may also attack tea-trees and their presence is made apparent by small piles of sawdust-like frass on the branch forks or near the base of the shrub. The safest method of control is to use a small syringe containing methylated spirits and squirt it into the hole made by the borer.
text from 'Bottlebrushes, Paperbarks and Teatrees
by Wrigley & Fagg, 1993, Angas & Robertson