Andy Whelton of Teagasc discusses the many commercial uses of Eucalyptus and the current interest and research on the species in Ireland
Native to Australia, Papua New Guinea and Indonesia, Eucalypts are widely cultivated throughout tropical and temperate areas including North and South America, Europe, Africa, China and India. They were first brought to the UK in seed form in 1774 to Kew with the first report of Eucalyptus planting in Ireland of Eucalyptus globulus at Garron Tower, Antrim in 1857. There are more than 700 species ranging from shrubs to 80-100m tall trees. Eucalypts provide a great variety of leaf and stem colour, bark and flowers. Most, however, can be kept as shrubs by cutting back each or every other year. This does no harm to the plant and their powers of regeneration are simply remarkable. They have this ability due to natural regeneration after fire or grazing in their native Australasia. A sense of maturity can quickly be brought to a new garden and the rapid growth of Eucalyptus can soon cover an eyesore.
HARDINESS
Key to the success of Eucalyptus is that seed is sourced from the correct provenance (exact place of origin) to ensure survival in our temperate conditions. Different provenances of the same species can differ considerably in their performance and survival. In general, only the stock of high-altitude Australasian origin should be sourced. In some cases, the environment they experience here is kinder than their natural habitat. The majority are hardy down to -14C and -18C. During the severe winter of 2009/10, when Ireland experienced some of the lowest winter temperatures ever recorded, Eucalyptus niphophila survived -17C in southern counties. However, some provenances of E. nitens were damaged. The importance of the correct selection of provenance cannot be overemphasised. Hardiness increases as the leaves change from juvenile to adult and the stem girth increases.
GROWTH
Eucalypts have evolved particularly successful ways of producing shoots which helps to explain their capacity for rapid growth and regeneration. These habits are quite unlike our native trees. Buds are present in the axil of every Eucalyptus leaf as it unfolds from the parent growing tip. These are called naked buds and are capable of rapid growth as soon as the parent leaf unfolds. The ones nearer the tips continue to produce new growth without limit and in the axil of each new leaf is another naked bud. The number of leaves that can separate from the growing tip is indefinite and the naked buds expand simultaneously.
Another feature of their growth is that they also develop lignotubers. They start life as swellings in the axils of the cotyledons or first few seedling leaves and tend to fold down the stem and bury themselves beneath the soil. They can produce very many leafy shoots if the crown is destroyed and will replace the original stem. They have this ability due to natural regeneration after fire or grazing in their native Australasia. Given the climate in Ireland, these evergreens continue to grow almost all year round and photosynthesize immediately once weather conditions are suitable.
AROMA
All Eucalyptus have oil-producing glands in their leaves which give their characteristic odour. They may also be in the bark and in the flowers. There are more than 15 essential oils found in the Eucalyptus genera with between one and four found in different combinations and quantities, in turn, producing a slightly different aroma for each one. The Aborigines found that oils from certain Eucalyptus had a beneficial effect on colds, influenza, toothache, headaches, fevers and skin soars. Eucalyptus oil is widely used for cleaning, as an antiseptic, for de-odorising and in foods such as cough drops and toothpaste. Certain oils are also used in the perfumery, drugs, disinfectants and deodorants.
COMMERCIAL USES
CUT FOLIAGE – Over 100 ha of Eucalyptus is cultivated in the South of Ireland for the floristry trade at home and abroad. A sheltered site is a prime requirement without which the young foliage, as it meets in the rows can rub against one another causing damage to the growing tips. After two seasons, cutting commences in October and continues until March in mild areas.
JUVENILE AND ADULT FOLIAGEPerhaps not fully understood, but there is a substantial difference between the juvenile, intermediate and adult foliage in some of the Eucalypts, e.g. E. perenniana. After two-three years the tree will stop making juvenile foliage altogether where the leaves tend to be broader and more upright with a brighter colour as opposed to when the leaves become adult they are longer, more drooped and duller in colour. If you require only the juvenile foliage, the only way is to coppice or cut back to a stump or frame at the end of March after at least two full seasons growth. This will force the tree to produce the suitable leaf shape desired by the florist trade. Whilst the main demand is for juvenile foliage with E. parvula and E. glaucescens being the main species, there are markets for some adult foliage and E. coccifera is suited for this purpose and should be pruned and not coppiced. Planting distance is commonly 1.5m giving 102 plants per ha.  BIOLOGICAL CONTROL OF PESTSIn Ireland, Psyllid (Ctenarytaina eucalypti) and an exotic leaf beetle pest, Paropsisterna selmani pose a risk to commercial Eucalyptus crops whether for foliage or other use including forestry. Psyllids (both adults and nymphs) can become established on the bloom of tender glaucous juvenile foliage where they surround themselves with a woolly excretion which is a mixture of honeydew and cast skins. Young trees or coppice regrowth is at most risk. The Eucalyptus beetle is a relatively new pest and can be more damaging on adult foliage. Gaining an understanding of the phenology of these pests and developing bio-control strategies have been the subject of Ph.D. studies in recent years. A parasitic wasp (Psyllaephagus pilosus) has been introduced under licence to control Psyllid where the female wasp parasitizes the Eucalyptus psyllid exclusively. The parasitic wasp Enoggera nassaui has been tested as a bio-control agent for use on the leaf beetle with success and its introduction into commercial plantations is the next step in ensuring a sustainable control strategy in the future. Careful monitoring and management of biological control agents are vital to their successful performance in outdoor crops. Glycerined foliage – successful methods have been developed for preserving Eucalyptus foliage through the use of Glycerine and dyes. Adding value to foliage by glittering and painting is an area that continues to be developed. Carbon sink – this is the fashionable term given to forests because of their major role in the planetary recycling of carbon, nitrogen and oxygen. Through photosynthesis, plants will combine carbon dioxide and water to produce sugars needed for growth. Therefore, they are critical in the adsorption of the rising levels of CO2 which lead to the greenhouse effect. Eucalyptus plantations can produce as much as ten times as much sustainable harvest as can native virgin forest and consequently absorb much higher amounts of CO2.  EUCALYPTUS AS A WOOD FUELIn recent times we have heard a lot about renewable energy and biomass. Willow and miscanthus have been promoted as energy crops for the production of wood chips and wood pellets. With the recent interest in the use of timber for wood fuel, Eucalyptus offers several environmental advantages over fossil fuel. Eucalyptus produces high volumes of dense timber suitable for wood chip, pellets and firewood logs. One of the characteristics of Eucalyptus is that the wood splits easily which makes it a delight to use for chopped firewood and an attractive proposition for owners of log burning stoves. 0.6 acres of Eucalyptus would give approximately the same heat value as 1000 litres of oil on an annual basis. i.e. 0.6 acres would produce equivalent energy as 8000 litres of oil when harvested at the end of eight years. Given the ability of the species to coppice, after felling the tree stumps will produce new growth which when thinned out to a single stem will give a new crop of timber after another eight years. This process can be repeated to give a third and final crop after which you must replant. One planting of Eucalyptus could, therefore, give you a 24-year rotation with three harvests if species that reliably coppice are used. There is currently a support programme from DAFM for growing trees including Eucalyptus species such as nitens and rodwayi amongst others for use as a domestic fuel.  HEDGING OR IN TUBSCertain species with the smaller size of adult leaf and a tendency to keep their lower branches can make an attractive 2-3 m hedge. The species coccinea and archeri are good examples. Pruning management, however, is important to maintain shape and this should start at the end of the second season’s growth to begin to shape them for a hedge. Remove a third of the height and cut to an inverted ‘V’ shape removing some of the side branches in September or April. The following year removes a third of the height again in a similar way shaping into an inverted ‘V’. Once the hedge has reached the required height cut back every year in September or April. Eucalyptus can also be grown in tubs but remember they grow fast and to accommodate the related root growth you must be prepared to re-pot into larger pots as the plant grows or alternatively prune as described for hedging. ‘NEW LEAVES’ RESEARCHGiven the current interest in Eucalyptus particularly for foliage and other uses, a DAFM funded project ‘New Leaves’ aims at improving and perfecting propagation methods through micropropagation and vegetative techniques to allow for rapid bulking of plant material of elite clones. The propagation work is also looking at using technologies to develop new lines specifically for cut foliage and is being led by Teagasc propagation expert Dr. Gerry Douglas and Dr. Farhana Alfrose of Teagasc Ashtown with the support of technician David Wallace in the glasshouse unit at Kildalton College. This innovative work is exciting those in the industry and the market and there will be an opportunity to see how the research work is progressing along with other aspects of Eucalyptus cultivation at a focused event due to be held on the 15 August in Kildalton College. The event should interest those growing Eucalyptus for ornamental purposes including hardy nursery stock, landscaping and cut foliage but also for forestry and biomass. ✽ |
 Andy Whelton M Sc Ag Sc is a horticultural development officer in the Teagasc Horticultural Development Department based in Teagasc Clonakilty College and is a specialist adviser on ornamental cut foliage. He has spearheaded the developments in cut foliage as a new sector in commercial horticulture. He also works closely with outdoor vegetables and protected crop businesses in Munster and south Leinster. You can contact Andy via andy.whelton@teagasc.ie. |
