Eucalypts – Propagation

Introduction

Eucalypts are usually propagated from seed. Vegetative propagation (i.e. cuttings), although possible under certain circumstances (such as the use of juvenile foliage) has practical limitations and is of little interest to the average grower. Some work on grafting has been carried out in an effort to extend the range where desirable species can be grown or for early flowering of ornamental species.

Seed

Seeds (and chaff) of the River red gum (Eucalyptus camaldulensis) Photo: Brian Walters

The seed capsules need to be collected and placed in an open container in a warm position until the fine seed is released. This should occur in 2-3 days. For best results, the capsules should be at least 12 months old (ie. the most recently formed capsules are best avoided). The seed capsules usually contain true, viable seed together with a considerable quantity of infertile seed known as ‘chaff’. The true seed is easily identified as it is usually larger and darker in colour than the chaff. Generally it is not necessary to separate the true seed from the chaff; both can be sown together and the chaff simply becomes part of the propagating mix.

Germination of the seed of Angophora, Corymbia and Eucalyptus species is usually quite easy by normal seed raising methods. In most cases no special pretreatment is needed, however, germination is improved with some high altitude species if the seed is “stratified” for a period of time. Stratification involves exposing the seed to a period of low temperature and is beneficial for those species normally found at high altitudes. The simplest method is to sow the seed normally in a punnet or pot, cover it and place the container in a refrigerator. The period required under stratification varies with the species and can range from 3 weeks (E.perriniana) up to 10 weeks (E.delegatensis).

A common method used for germination of eucalypts and related plants is the “bog method” where the pot containing the seeds is placed into a saucer of water until germination occurs. This results in moisture reaching the seeds by capillary action and ensures that the seeds do not dry out.

Although germination will occur right throughout the year, germination is usually slower, more uneven and percentage not as high during the period from May to mid-August. During this period germination may take from 2 to 3 weeks, compared to 3 to 10 days during spring and summer.

Grafting

A number of horticulturally desirable species are found in the south-west corner of Australia and have proven to be unreliable in humid, coastal areas of the eastern states. Species in this category include the popular “Red flowering gum” (C.ficifolia), the “Mottlecah” (E.macrocarpa) and E.caesia. All of these have large, colourful flowers and are desirable garden subjects. Grafting has shown some potential for extending the horticultural range of some of these species but the long term viability is not certain. Most work has been done on C.ficifolia using the related C.gummifera as rootstock.

General Propagation

Further details on general plant propagation can be found at the Society’s Plant Propagation Pages.

Eucalypts – Cultivation

Introduction

Eucalypts have proven to be reliable and adaptable over a wide range of environments but many are too large for small suburban properties so some care is needed in their selection. In addition, consideration needs to be given to the natural environment and climate of the species being considered. If this is vastly different to that of the local environment, alternative selections may be more satisfactory. The table below summarises features of about 20 popular species as well as indicating some selection criteria for each.

Eucalypts for Cultivation

Pests of Eucalypts

There are quite a number of pests which can attack eucalypts and which may require control in a garden situation. Leaf chewing insects are probably the main concern but, unless damage is severe, there is little reason to resort to chemical controls. Regular observation will enable removal by hand for trees which are being established and, if a few chewed leaves can be tolerated, birds will often keep the infestations in check on larger specimens.

Sometimes insects such as “Christmas beetles” can appear in plague proportions and cause severe defoliation which is beyond the ability of the bird population to control. If access is possible, the beetles can be shaken off, collected and disposed of.

Another chewing pest that can appear in large numbers are steel-blue sawfly larvae. They do most of the damage to a tree’s foliage during the night and in daylight hours they gather into groups around small branches. If they are accessible at these times they can be removed by cutting off the branches where they cluster together.

Psyllids (including lerp-forming species) and scale can also cause problems. These are sap-sucking insects and can cause a tree to lose vigour. Again, birds will normally keep them under control but often a strong jet of water directed at the pests will also dislodge them. This may need to be carried out several times. If this is not successful, the traditional treatment with white oil is usually effective.

Some insects lay their eggs into leaves or twigs forming “galls” in which the next generation develop. The galls form as a response by the plant to secretions by the particular insect. To prevent hatching of the adults, galls can be removed by hand and burnt. Often, however, only a few galls occur and are unlikely to damage the tree to any serious extent. They are sometimes attractively coloured and of interesting shapes which can be appreciated as part of the local garden environment. Wasps, flies and thrips are among the gall-forming insects.

People sometimes worry about the appearance of mistletoe on a tree but this is usually unwarranted. These parasitic plants are commonly seen on eucalypts as ovoid-shaped clumps of foliage hanging from the tree’s branches.

Mistletoes and their hosts have evolved together and, unless the host tree is unhealthy, one or two mistletoe clumps should not cause any problems. In fact they can also be enjoyed as part of the overall garden environment and the fruit may attract the beautiful mistletoe bird.

Once a tree gets to a reasonable size, control of pests by hand removal will be impractical. If serious damage is being caused, it may be necessary to seek advice from the local Agricultural Department.

For further information on mistletoes, see the excellent two-part article by Marion Jarratt published in Australian Plants online. Part 1 is here and Part 2 is here.

Volatile Oils from Eucalypts

Ken Stuckey

The following article is based on one which was published in the November 1985 issue of the newsletter of the Eucalyptus Study Group. Some minor editorial amendments have been made where necessary to bring details up to date.

Essential oils are the aromatic ‘essences’ found in various plant parts. Because they evaporate when exposed to the air at ordinary temperatures they are called volatile or essential oils. These oils possess characteristic odours, are colourless, insoluble in water and are separated from plant material by steam distillation or solvent extraction.

Essential oils from the leaves of eucalypts have attracted interest since the earliest days of settlement in Australia. One of the first articles of export from the newly established colony of New South Wales in 1788 was a quarter of a gallon of an essential oil steam-distilled from the leaves of a eucalypt (Eucalyptus piperita) growing on the shores of Port Jackson.

The therapeutic properties of the Australian flora so fascinated the botanist Baron Ferdinand von Mueller that he prompted a Victorian pharmacist colleague, Joseph Bosisto, to investigate the commercial production of eucalyptus oil. Bosisto responded and, in 1852, commenced operations at Dandenong, Victoria. This was the beginning of the Australian essential oil industry. Between 1854 and 1891 Bosisto displayed commercial eucalyptus oils at no less than seventeen exhibitions around the world. Through his pioneering efforts the eucalyptus industry spread to other states as the demand grew and its products became known in world trading centres. By 1900 the industry was firmly established, and for the next fifty years Australia remained the world’s largest supplier of eucalyptus oil.

One problem confronting the industry from the outset was the variation in the oils marketed. At the turn of the century, new light was thrown on the problem by two early curators of the Museum of Applied Arts and Sciences, Sydney, in a series of investigations into the botanical classification of the eucalypts and their oils. Further progress was made by successive curators at the Museum with the discovery of chemical variation within species, a phenomenon which had been troublesome to distillers. The curators found that populations of E.dives at Braidwood yielded piperitone and phellandrene, whereas cineole-rich oils were obtained from populations of the same species at Tumbarumba.

There are over 700 species and varieties of the eucalypt but only about 20 have been exploited commercially and less than a dozen are presently of economic importance. The commercial eucalyptus oils are broadly divided into three classes; medicinal, industrial and perfumery oils, according to their specific uses.

• Medicinal oils — the active therapeutic agent of medicinal oils is cineole, of which a minimum of 70% is required to meet commercial specifications. Medicinal oils are graded on their cineole content, and it is common practice to improve them by blending and purification. These oils are used for inhalants, embrocations, soaps, gargles, sprays, lozenges and dentrifices. Eucalypt species which contain commercial quantities of cineole are E.polybractea, E.radiata, E.dives, E.sideroxylon, E.leucoxylon, E.goniocalyx, E.viridis, E.smithii, E.cneorifolia, E.globulus, E.dumosa and E.oleosa.
• lndustrial oils — these contain phellandrene and piperitone as the principal constituents. Phellandrene oils are used in the manufacture of inexpensive disinfectants, household and industrial liquid soaps, and germicidal preparations. Piperitone oils provide the base material for the manufacture of synthetic menthol and thymol. Species used to provide these oils are E.dives, E.elata and E.radiata.
• Perfumery oils — two species of eucalypt have been exploited to supply oils for the perfumery industry: E.citriodora now (Corymbia citriodora) for citronellal and E.macarthurii for geranyl acetate and eudesmol. Extraction of these oils in Australia is no longer economically viable.

Eucalyptus Study Group

The Eucalyptus Study Group is one of a number of Study Groups within the Australian Native Plants Society (Australia). Its aim is to further knowledge about the cultivation, propagation and conservation of the eucalypts (the genera Eucalyptus, Corymbia and Angophora). Members of the Group are mainly keen amateurs with no formal horticultural or botanical knowledge, although a number of professionals in those fields also participate. As in all study groups, the members’ work is mainly carried out in their own homes and gardens and in their own spare time.

Further information about the Study Group, its activities and access to the newsletter archive can be found at the link below.

***Click here to go to the Eucalyptus Study Group***

Eucalypts – Further Information

Most books dealing with Australian native plants will contain useful information on the botany and horticulture of eucalypts. There are also a number of eucalypt resources on the internet and on CD. Some of the most detailed references are listed below.

Books:

• Boland, D, Brooker, M, Chippendale, G, Hall, N, Hyland, B, Johnston, R, Kleinig, D and Turner, J (1984), Forest Trees of Australia, Thomas Nelson, Australia and CSIRO.
• Brooker, M and Kleinig, D (1990; Revised Ed.), Field Guide to the Eucalypts, Vol.1 South-eastern Australia, Inkata Press, Melbourne and Sydney.
• Brooker, M and Kleinig, D (1990), Field Guide to the Eucalypts, Vol.2 South-western and Southern Australia, Inkata Press, Melbourne and Sydney.
• Brooker, M and Kleinig, D (1994), Field Guide to the Eucalypts, Vol.3 Northern Australia, Inkata Press, Melbourne and Sydney.
• Brooker, M and Kleinig, D (1996), Eucalyptus: An Illustrated Guide to Indentification, Reed Publishers, Australia.
• Chippendale, G (1968), Eucalyptus Buds and Fruit, Australian Government Publishing Service, Canberra.
• Chippendale, G (1973), Eucalypts of the Western Australian Goldfields (and the Adjacent Wheatbelt), Australian Government Publishing Service, Canberra.
• Elliot, W. R and Jones D (1986), The Encyclopaedia of Australian Plants, Vol.4, Lothian Publishing Company Pty Ltd, Melbourne.
• Hill, K and Johnson, L (1995), A Revision of the Bloodwoods, Genus Corymbia (Myrtaceae), in Telopea, Volume 6(2-3), Royal Botanic Gardens, Sydney.
• Holliday, I and Watton, G (1989), A Gardener’s Guide to Eucalypts, Hamlyn Australia
• Kelly, S (1969), Eucalypts, Vol.1, Thomas Nelson, Australia.
• Kelly, S (1978), Eucalypts, Vol.2, Thomas Nelson, Australia.
• Prior, L and Johnson, L (1971), A Classification of the Eucalypts, Australian National University Press, Canberra.

CD-ROM:

• EUCLID; This is a computer-based, interactive identification and information system. It allows the user to quickly and easily identify any of the 324 species and subspecies of Eucalyptus and Angophora native to south-eastern Australia, i.e. New South Wales, Australian Capital Territory, Victoria, Tasmania and part of South Australia.

Journals:

Many issues of the Society’s journal “Australian Plants” contain material on eucalypts and eucalypt cultivation. Issues of particular interest are:

• Vol 8, No.61 December 1974; Small Eucalypts, with particular reference to colourful mallees.
• Vol 9, No.72 September 1977; Forms of Eucalyptus leucoxylon.
• Vol 10, No.78 March 1979; Eucalypts for arid areas; Eucalypt propagation; A close look at Eucalypt leaves; Scribbly gums; Root systems.
• Vol 11, No.88 September 1981; Descriptions and photographs of yellow-flowered species; Pests of Eucalypts.
• Vol 20, No.164 September 2000; Ornamental Eucalypts – Species for cut bud and flower production.
• Vol 22, No.176 September 2003; Eucalypts in the Goldfields.

Internet:

• Eucalyptus Study Group Newsletters – recent issues can be found here.

• Corymbia, Corymbia….Wherefore Art Thou, Corymbia? – a look at the naming controversy
• Corymbia ‘Summer Red’ and ‘Summer Beauty’
• Currency Creek Arboretum – specialist eucalypt research arboretum.
• Dyeing with eucalypts
• Eucalypt Australia – A grant making Charitable Trust that focuses on eucalypts and co-ordinates National Eucalypt Day (March 23).
• Eucalypts by Cuttings.
• Eucalypts…but not Eucalyptus – The new genus Corymbia
• Eucalyptus oil industry in the NSW Southern Highlands – A two-part article from the Southern Highland News, sourced from the archives of Berrima District Historical & Family History Society. Part 2 is here.
• Growing Native Plants – a series of plant profiles by the Australian National Botanic Gardens; includes a number of eucalypts.
• Hardy Eucalypt Page – Eucalypts for Cold Climates
• Medicinal properties and bush foods of eucalypts
• The marri, Corymbia calophylla
• Mistletoe – Part 1
• Mistletoe – Part 2
• Small-growing Eucalypts
• Small Gums for Small Gardens
• Stratification of Eucalyptus Seed
• Temperate Area Eucalypts
• When to Plant Eucalyptus Seed