To help secure additonal funds for research (which would be matched by grants from RIRDC), ANFIL offers a sponsor package which lists products and companies specialising in supply of raw and value added lemon myrtle products. Contact rus@anfil.org.au for details.

Description:

Growing information:

Lanceolate leaves are reddish brown when juvenile, fresh green when mature, 50-100mm long, with slightly serrate margins, an acute apex and visible venation.
Strikingly pretty white aromatic flowers form in November or December. They are numerous on long stalked clusters. Single flowers show a bell shaped hairy receptacle with 5 persistent spreading calyx lobes, topped by 5 small petals and fluffy stamens about 10 mm long, about half the size of the petals.
Fruit is a small capsule with small seeds.

In the wild, trees occasionally reach 20 metres in height.

Introduction:

Lemon myrtle performs well in the garden and has been used as an attractive ornamental tree in landscapes and home gardens for many years. This information below is particularly pertinent to commercial operations.

Seedlings are hard to germinate and often form small side branches taking root on the ground.

Cutting-grown plants usually do not grow to the same size as seed-grown trees and typically are large shrubs to small trees.

Cuttings from semi hardwood are hard to strike.

Source:
Kibbler, H., Johnston, M.E., and Williams, R.R., 2004, Inhibition of Adventitious Rooting in Backhousia Citriodora F. Muell. Cuttings Correlate With the Concentration Of Essential Oil, The University of Queensland, Gatton.

Kibbler, H., Johnston, M.E., and Williams, R.R., 2004, Adventitious root formation in cuttings of Backhousia citriodora F. Muell: 1. Plant genotype, juvenility and characteristics of cuttings, School of Agriculture and Horticulture, The University of Queensland, Gatton Campus, Gatton Australia.

Climatic and soil requirements:

Lemon myrtle grows naturally in a sub-tropical climate in areas with < 800mm rainfall.
The tree prefers a nutrient rich soil of medium to heavy texture in a well-drained, wind-protected sunny position. Young trees are particularly frost and drought tender and require irrigation during dry spells.
The trees prefer neutral instead of acid soils and are prone to yellowing in alkaline soils. Once established, the trees are relatively hardy and recover quickly from dry spells.

Plantation layout:

Plantation layout needs to take several variables into account:

• Northerly aspects maximise sunlight and flat, free draining soils are preferred for mechanical harvesting, however River flats are not suited, as the trees will succumb to waterlogging.

• Ideally, orientation of rows should be north/south to provide equal amount of sunlight to all plants all-year round. This is not always possible due to property layout. A balance needs to be found between being able to effectively mow/slash and access between rows with machinery, minimise erosion and maximise sunlight.
• Cutting grown plants can be spaced at 1- 2.5m apart in single or multiple rows. Inter-row spacing depends on machinery used for maintenance or harvesting.
• Mono-cropping is advisable for mechanical harvest.

Wind protection:

Wind protection for cutting grown lemon myrtle is essential as the trees are prone to wind damage and easily snap off at the base of the trunk. Regular pruning will lessen the threat and selected windbreaks or shelterbelts can lessen the impact of prevailing winds during the stormy season as well as filter hot air which can cook the leaves on the trees. Native windbreaks can add biodiversity values to the plantation area, reduce moisture requirements and provide habitat for insect predators; however the selection of native trees for the windbreak needs care as some trees may be allopathic to lemon myrtle or increase disease potential.

Varieties:

Two main varieties have dominated the plantation grown lemon myrtle in the last ten years. The line commonly referred to as “Limpinwood” is hard to strike as a cutting, however it presents superior ornamental presentation, high biomass production and high oil yield as well as high citral content. The other variety, commonly referred to as Line B or Eudlo clone is relatively easy to strike, vigorous but slightly lower in biomass, oil and citral yield. Most commercial plantations have been supplied by specialist nurseries or contract propagated.

Water requirements:

At the moment there is only limited information available on the water requirements of lemon myrtle. Lemon myrtle grows naturally in areas of above 800mm rainfall and is prone to suffer from drought, especially when young.

• Excessive irrigations, leading to extended periods of waterlogging, should be avoided, as this tree does not like ‘wet feet’!

• Cutting grown lemon myrtle does not have a deep taproot and requires ample surface moisture and mulch to maintain leaf productivity in dry seasons.

• Extremely dry soil conditions should also be avoided.

• Within their range, plants normally experience a wet summer/autumn and dry winter/spring rainfall pattern.

Most importantly, growers should monitor and record their irrigations and soil moisture status using instruments such as tensiometers. This will help them and their advisors assess their current situation and practices, identify any problems and refine their future management.

Nutrition:

The nutritional requirements for lemon myrtle are not well documented, but the trees grow best in rich, fertile soils and need increasing amounts or organic fertilisers as they are maturing. The trees can be cut up to three times/year and as each harvest removes a large amount of biomass, it is essential to return nutrients for long-term productivity. As experience with the crop accumulates firmer guidelines and objective assessment techniques, such as leaf analyses will become available. Until then, some general principles should be kept in mind when designing a fertilizer program:

• Many Australian native plants are intolerant of high phosphorus levels, so a relatively low P fertilizer, suitable for natives, should probably be used.

• In the first season following establishment the aim should be to maximise growth to develop a good plant structure and produce several flushings.

• Once established, nutrient availability is necessary to promote vigorous vegetative growth after harvesting.

• Documented regular observations, soil and corresponding leaf analyses will assist any grower to adjust their fertilizer regime.

Pest and diseases:

Lemon myrtle has shown a remarkable resilience to pests and diseases, however it can be affected by sooty moulds – especially if in close proximity to other native trees (shelterbelt) that foster it. The occasional attack of the Monolepta beetle (Monolepta australis) on juvenile leaves can be observed – however no permanent damage has been reported.

Canopy management:

Plants need to be pruned regularly within the first years to provide a “shrubby” shape and to increase leaf production. It is recommended to avoid top-heavy leaf mass as the trees easily snap off at the base in storms or wind gusts.
Regular harvesting of leaf increases leaf production and keeps the tree from becoming woody.
Woody trees are best pruned heavily to increase subsequent yields.

Harvesting and Handling:
In Australia, lemon myrtle leaves can be harvested all year round. Lemon myrtle harvested in Northern Queensland may be restricted in the traditional Monsoonal rainy periods.
Commercially available leaf products are typically cut from the tree and immediately after harvest placed into a drying unit. Some leaf is dried on stem, others are stripped off the stem for drying. Various different methods are used within the industry to achieve a quality end product. The dried leaves are then processed (milled) to suit the application.
Research suggests that variation of drying temperature may affect the retention of citral and has an impact on retention of colour
Source:
http://rirdc.infoservices.com.au/downloads/04-125.pdf
http://www.rirdc.gov.au/programs/new-rural-industries/new-plant-products/native-foods/native-food-fact-sheets.cfm

Buchaillot, A., Caffin, N., Bhandari, B., (2009) Drying of Lemon Myrtle (Backhousia citriodora) Leaves: Retention of Volatiles and Colour, Drying Technology, Volume 27, Issue 3 March 2009, pages 445-450.

Yields:
Yields will vary with variety, orchard fertility and management. Comprehensive data is not available at this present time.

Author: : Sibylla Hess-Buschmann
Contributors: Rus Glover, Chris Read.
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