Lemon Myrtle

24.05.17

Lemon myrtle (Backhousia citriodora) is the giant of the Australian native food industry. Its annual production may be up to 1,000 tonnes (fresh leaf weight), compared with 5–15 tonnes of annual production for most other native food crops and less than five tonnes for a few crops in the industry. Lemon myrtle is a medium-sized native tree (3–20m) originating in subtropical coastal rainforests of Queensland. The tree produces intensely flavoured leaves with a distinctive lemon/lemon grass fragrance and taste.

Overview

The potential uses of lemon myrtle have been recognised for over a century by European settlers, and the tree has long been cultivated in home gardens and small cottage-style enterprises. The leaves are used as a culinary herb, tea or spice. Alternatively, oil can be distilled from the leaves and used as a flavour agent for food and in a wide range of personal care products. Commercial production of lemon myrtle in Australia commenced in the mid-1990s.

The lemon myrtle industry is made up of approximately 60 small- and medium-sized businesses in northern New South Wales and south east Queensland; and one very large operation in northern Queensland.

Facts and figures

  • Citral is the ingredient that gives lemon myrtle its distinctive lemon fragrance and taste
  • Lemon myrtle essential oil contains up to 98% citral, which is considerably more than the citral content of other lemon-flavoured oils derived from citrus (3–10%), lemon grass (75%) and tropical verbena (74%)
  • Lemon myrtle essential oil was first distilled in 1888 and reported as an essential oil extremely rich in citral
  • During World War II a national drinks company, Tarax, used the essence of lemon myrtle to flavour drinks when natural lemon essence was in short supply
  • Lemon myrtle is used in tea, herbs, spice and personal care products, and potentially as a food preservative and cleaning agents

Production status

Accurate information is not readily available for the native foods industry but a recent stocktake of the industry provides good estimates of industry characteristics, production figures and product value.

There are approximately 60 small and medium-sized businesses in northern New South Wales and south east Queensland who produce lemon myrtle to supply contracts for raw product, i.e. leaf or oil, to processors and larger manufacturers. These businesses will grow lemon myrtle in a single species stand, and they may also have stands of other native food trees. These operations vary from small, 1,000 to 4,000 lemon myrtle trees, to medium-sized, with 10,000–15,000 trees. The medium-sized businesses may buy additional harvested leaf from smaller growers and process it with their own harvest. Small and medium-sized growers may also form groups to process and market their lemon myrtle products.

There are some small businesses in the northern New South Wales area that have plantations of mixed species where lemon myrtle is planted with other trees such as anise myrtle, cinnamon myrtle, Davidson plums and sometimes round or finger limes, lemon-scented tea trees, riberries and other species. The concept was based on not creating a monoculture, which provides good pest and disease management, however machine harvesting is not possible and therefore production volumes are limited. This system suits an operation that value-adds and markets its own product.

In northern Queensland there is one very large operation, with over one million trees planted. This business grows, processes and markets its own material; and accounts for about 50% of Australian production.

Although lemon myrtle is an Australian native, it has established well in plantations in Malaysia and China. It is anticipated that product from these areas will have lower labour costs and provide strong price competition for Australian product in the future.

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Map of current and potential growing regions

Uses

Lemon myrtle leaves are used fresh or dried as a culinary herb and tea, and dried as a spice. The fresh leaves can also be steam distilled to produce lemon myrtle essential oil, which is used as a food-flavouring agent in sweet and savoury applications. As a leaf product, it can be used instead of lemon grass in cooking, and in leaf or oil form it is popular in curries, pasta, cheesecakes, ice-cream, breads, dressings, sauces, drinks and syrups.

The essential oil of lemon myrtle may be used in a wide range of personal care products such as soaps, creams, toothpaste, shampoos and conditioners.

Lemon myrtle is high in anti-oxidants, vitamin E, lutein (a carotenoid compound important for eye health) and calcium, and has potential as a functional food.

The antimicrobial and antifungal properties of lemon myrtle oil have been recognised for nearly a century, and recent research confirms that these properties are superior to tea tree oil. There are potential applications of lemon myrtle as a natural food preservative and as a natural surface-cleaning agent.

A number of research projects have been conducted to understand and investigate the properties of lemon myrtle, and other native foods, including health benefits and health-enhancing compounds in native foods, physiological activities of native foods, nutritional data, defining the flavours of native foods, and using native oils for the management of postharvest diseases of horticultural crops.

Production Requirements

Growing regions

Lemon myrtle grows naturally in subtropical and tropical regions but it has been commercially cultivated in all states of Australia, except Tasmania. The main growing regions are the Northern Rivers region of New South Wales and the adjoining region across the border in south east Queensland. There is also a significant operation in the Whitsunday area of north Queensland. Small-scale operations also exist in Victoria, South Australia and Western Australia.

Soil type

Lemon myrtle requires well-drained, nutrient-rich soils of medium to heavy texture. The tree grows better on neutral soil than it does on acid soil, and it is prone to yellowing on alkaline soils.

Well-drained soils are essential, so while river flats may have suitable fertility and texture, they are prone to waterlogging and not suitable for planting lemon myrtle.

Climate

Lemon myrtle trees prefer a climate with annual rainfall greater than 800mm. However, distribution of moisture throughout the year is more important than annual rainfall total. Even in rainfall areas greater than 1000mm, growers will irrigate in the dry season or dry months to maintain adequate soil moisture.

Young trees do not tolerate drought and will require irrigation during dry spells. However, once established, the trees are relatively hardy and recover quickly from dry spells.

Young trees are particularly frost tender so plantations should be established in frost-free regions or frost protection provided. Once established, lemon myrtle trees can tolerate frosting but their biomass production will be less than trees growing in frost-free regions.

Varieties

Most commercial plantings of lemon myrtle are based on two selections (referred to as lines within industry and nursery circles) propagated by specialist nurseries.

The predominant variety planted is Line B, sometimes referred to as the Limpinwood selection, which has superior ornamental presentation, high biomass production and high oil yield. The oil of this variety has a high citral content of 96–98%. Preliminary observations suggest Line B is exhibiting better resistance to myrtle rust than Line A (all other selections from within the industry). Cuttings from this variety are difficult to strike and specialist nurseries are used as a source of planting stock.

The other selections within the industry are jointly referred to as Line A (and sometimes referred to as the Eudlo clone)It is a vigorous plant but is slightly lower in biomass and oil production than Line B. The Line A citral content is 90–93%. This line is relatively easy to strike.

Formal variety development will be more likely in the future, as a breeding trial comprised of all known provenances was established in northern New South Wales. The key focus of the trial in the first instance was myrtle rust resistance, in association with oil yield and product quality as other key parameters to be maintained.

Planting and crop management

Plantation layout is important to optimise growing conditions for the trees. The field should have a northerly aspect to maximise exposure to sunlight, and ideally, the rows of plants should run north–south to give equal sunlight to all plants, year round. Plantation layout also needs to take into consideration the best design for machinery access and minimising soil erosion, therefore a compromise of true north–south rows may be needed.

The plantation is established using plants grown from cuttings, and these are placed in cultivated planting rows, 1.2–1.5m apart in single rows. The spacing between rows will be determined by the width of machinery that is used for maintenance and harvesting, but is generally 3–4m wide. Planting density generally averages about 2500 trees/ha.

Seedlings require irrigation to ensure good establishment and mulching will assist with moisture retention in the soil.

Lemon myrtle trees easily snap off at the base of the trunk, particularly when trees are around 60–80cm tall, because stock grown from cuttings has poor root development. The plantation should be protected from wind or managed to reduce wind damage, such as regular pruning and windbreaks or shelterbelts to lessen the impact of prevailing winds, especially during the stormy season. Other species can be used for windbreaks however care should be taken with species selection as some may increase disease potential in lemon myrtle.

There is limited information on the water requirements of lemon myrtle. Irrigation should be available, especially when trees are young and as the plantation establishes. Extremely dry conditions should be avoided. Lemon myrtle grown from cuttings does not have a deep taproot, so it depends on ample surface moisture and mulch to maintain leaf productivity in dry seasons. Irrigation throughout the dry season is recommended, however it must be carefully managed to avoid extended periods of waterlogging. Soil moisture monitoring equipment, such as tensiometers allows for accurate soil water management.

The nutritional requirements of lemon myrtle are not well documented. Trees can be harvested up to two times each year, with each harvest removing a large amount of biomass. Even on fertile soils, it is essential to return nutrients for long-term productivity. As more experience is gained with crop management, objective nutrient assessment techniques will become available.

Pruning of lemon myrtle should occur regularly within the first years to manage leaf mass and shape the trees into a hedge about 2–3m tall. Leaf mass needs to be managed in the first few years as trees can become top heavy and snap at the base in storms and winds; once trees reach about three years of age and have grown into a hedge, this is less of a problem. Once established, regular harvesting increases leaf production and keeps the tree from becoming woody. On occasion, established trees may require pruning (in addition to harvest) to reduce woody material and increase subsequent yields.

Weeds, pests, and diseases

Weeds need to be controlled at seedling establishment to reduce competition for nutrients, water and sunlight. Mulching the planting row will help suppress weed growth. Hand weeding is required on occasion to remove rainforest trees, such as camphor laurel, that germinate from seed spread by birds. Once established the lemon myrtle has a heavy leaf growth to ground level, preventing weed growth under the tree. Kikuyu is managed by running the mower underneath the leaf canopy, a short way into the hedgerow.

Historically, lemon myrtle has had a remarkable resilience to pests and disease with sporadic outbreaks of sooty moulds—especially if the plantation is in close proximity to other native trees that can harbour the moulds. Occasional attacks of the monolepta beetle (Monolepta australis) have been observed during flowering but permanent damage has not been reported.

Recently, myrtle rust became a serious disease concern for several native food species, including lemon myrtle. Myrtle rust is a fungal disease first found in Australia in April 2010 but by December 2011, it had spread from Cairns in far north Queensland to Victoria. Left untreated, the disease can cause deformed leaves, heavy defoliation of branches, dieback, stunted growth and even plant death. 

Infrastructure Requirements

The cultivation of lemon myrtle requires standard equipment for plantation maintenance such as a tractor, mower or slasher, and sprayer.

An irrigation system and soil moisture monitoring equipment is required if production is to be maximised.

For businesses with less than 10,000 trees, harvesting and drying equipment is not a viable investment. Smaller sized growers will use a contractor for harvest and drying.

Harvest equipment is based on modified vineyard pruning saws mounted on the front of a tractor, which cuts the material from the trees in a triangular hedge. There is no standard harvesting equipment because the industry has had to modify machinery used in other horticultural enterprises. The equipment, however, requires the capacity to collect the leaf material once it is cut, which may involve sweepers attached to the tractor that transfer the cut material into a trailed bin. Some bins are custom-designed to fit into the drying facility, eliminating the need to handle the product between harvest and drying.

If trees are well-managed and harvested at least twice a year, pruning will not be necessary. However, if trees do require pruning, tractor-mounted pruning saws are used.

The need to own distillation equipment will depend on the nature of the business, and whether or not the producer is value-adding their own product or providing leaf to a contract drier and distiller.

Harvesting & Processing

Plantation lemon myrtle may be harvested mechanically or manually. Larger operations (more than 1,000 trees) are harvested mechanically. Lemon myrtle can be harvested all year round but location, operation size and end product will influence the harvest regime. A commercial operation should strive for two harvests each year. In northern Queensland, harvest may be restricted during the traditional monsoonal rainy period. Large operations tend to undertake a major harvest two times a year, whereas smaller operations may harvest when orders are secured.

At harvest, leaf and stem material is cut from the tree. Depending on the end product and quality required, leaf may be dried on the stem or stripped from the stem before drying. The leaves must be dried quickly to preserve the citral content. The dried leaves are milled or ground according to end product requirements, and then stored in dark, temperature-controlled environments.

Lemon myrtle essential oil is produced by steam distillation of the fresh leaf and stem material. Distillation should be carried out as soon as possible after harvest to ensure the highest quality oil. If the trees are overgrown and have thick stems (greater than 30mm), the harvested material may be chipped before distilling.

The dried leaf and extracted oil may be further processed and packaged on farm and sold as value-added product; or they may be sold as raw product to distributors, wholesalers or processors for further manufacturing.

Markets & Marketing

Producers of small volumes of lemon myrtle generally process and value-add their own product, and market their product locally, through farmers’ markets and online. Sometimes, several producers will work together under this enterprise model.

Lemon myrtle producers who have sizeable plantations (1,000–4,000 trees) sell their leaf to a processor, who may also be a lemon myrtle producer. Alternatively, small- and medium-sized growers may form groups to process and market their leaf and oil products. A single large producer in northern Queensland, processes and markets its own product entirely.

Almost 90% of lemon myrtle leaf produced in Australia is exported in the dried form. The European Union and the United States are the major markets, where lemon myrtle is consumed as tea or used as spice. The Global Financial Crisis and continued financial stress in the key markets had a dampening effect on export demand. Domestically, lemon myrtle products are sold through native food retailers, farmer markets and online sales.

The market for lemon myrtle is regarded as stable and likely to remain a niche market in the foreseeable future.

Risks & Regulations

Risks/challenges

There are several challenges common to all native food producers and their industry more broadly, such as annual variation in production volume, low return on raw product, and concurrent oversupply of niche markets and undersupply of potential large-scale markets.

While lemon myrtle is an exception to the general industry in terms of having a reliable supply of product, medium and smaller-sized producers are more vulnerable to economies of scale in the face of variable consumer demand and an oversupplied market of value-added products.

Lemon myrtle is produced in five countries overseas at lower cost than Australian product, so maintaining a competitive advantage through quality and reliability is critical; and remains challenging with ongoing economic stress in Europe—the major market for Australian lemon myrtle. Synthetic and substitute sources of citral also present a challenge for maintaining and growing markets.

A major risk to the productivity of lemon myrtle trees is the fungal disease, myrtle rust, which affects a range of species and native food plants. Left untreated, the disease can cause deformed leaves, heavy defoliation of branches, dieback, stunted growth and even plant death. 

Regulatory considerations

Currently there are no industry-wide product descriptions or quality standards developed for lemon myrtle. Some producers of lemon myrtle products choose to participate in Freshcare, which is currently the largest Australian on–farm assurance program for fresh produce for on-farm food safety and quality and environmental certification services.

When processing raw product into value-added food products, consideration should be given to food standards regulations. Further information can be found at the websites of Freshcare, HACCP and Food Standards Australia New Zealand.

Image Gallery

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Lemon myrtle under commercial production

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Lemon myrtle tree in flower

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Lemon myrtle leaves

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Myrtle rust on lemon mytle leaf

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Ground lemon myrtle