Brown boronia is native to the south west of Western Australia. A perennial shrub growing to 1–2 metres in height, it has small aromatic leaves and in springtime, it produces flowers that have a very intense and attractive fragrance. The flowers are usually deep chocolate brown on the outside of the cupped petals, and bright yellow on the inside, however there is some variation in colour between types.

While both leaves and the flowers are fragrant, only the flowers are used for production of essential oil/extract. The purified oil extract has been available on the world market since the 1920s. Traditionally, brown boronia was harvested from wild stands in Western Australia for cut flowers and essential oil production, however this has now stopped due to the risk of disease being spread through native plant communities. Brown boronia has been farmed since the mid-1980s, mainly in Tasmania.

Boronia oil/extract is used in perfumery and as food flavouring with the major markets being United States of America and Europe. It is also used in aromatherapy.

The boronia oil/extract industry is classified as a maturing industry in Australia and the interests of its growers and producers are represented by The Essential Oils Producers Association of Australia.

Facts and figures

• Boronia oil/extract is extracted from the flowers of Boronia megastigma, which is native to Western Australia
• Boronia is difficult to establish and manage — plants are propagated from cuttings which are susceptible to root rots and rust
• The oil/extract is extracted by a complex solvent extraction process
• 30 hectares of boronia is in production in Australia, yielding two tonnes of flowers per hectare
• The markets for boronia oil/extract are highly specialised and entrants to the industry should consider producing boronia oil/extract under contract

Growing regions

Brown boronia is endemic to the south west of Western Australia, where it is commonly found as an understorey species. However, most of the commercial boronia farms in Australia are based on the north and east coasts of Tasmania.

The most suitable growing regions for brown boronia have been identified as the coastal regions of the South West of Western Australia, the north, north east and east coasts of Tasmania, and southern coastal regions of Victoria.

Soil type

Boronia has reasonably specific soil requirements, preferring a soil pH_(water) between 4.0 and 5.0, however trials have shown the plant will grow in soil with a pH of as low as 3.5 and as high as 6.5. The soil should have high organic and low clay content, with high flower production being obtained on well-drained acid sands. The natural vegetation on this preferred soil type is usually a coastal heath or bracken fern.

Soil should be tested for phytophthora and nematodes and also for residual phosphorus as boronia, like many Australian natives, does not tolerate high levels of phosphorus. Boronia does not like warm moist soils and losses from root rots may occur in these conditions.

Climate

The cool temperate regions of Western Australia, Victoria and Tasmania are well suited to boronia production, particularly the coastal regions of these areas. Brown boronia is reasonably hardy and can survive temperature extremes, from the dryness of a Mediterranean-type climate to the frost and snow of Tasmania.

The rainfall in these suitable growing areas is generally sufficient for production, however irrigation is recommended for young seedlings and for maximum flower yield.

Temperature and photoperiod requirements for boronia are quite specific. The plant will remain vegetative at temperatures higher than 25°C and any flowers that have initiated will most likely abort. A cool period is required for boronia to initiate flowering. In autumn, the ideal weather conditions for maximum flower number are approximate night temperatures of 10°C, day temperatures of 15°C, a 10-hour day length and full to 50% sunlight. These requirements may restrict the climatic range in which boronia can be commercially produced.

Varieties

Commercial varieties for oil/extract production from Boronia megastigma have been selected for improved yield, agronomic performance and disease resistance, however these are only available through a licence agreement with the owners of the lines.

Planting and crop management

Strong winds can damage boronia plants so windy sites should be avoided or windbreaks considered. Land preparation may be as little as minimum tillage and planting as the site presents itself; alternatively, the site may be cleared and levelled to remove large tree roots, which may be a source of soil-borne diseases.

The main infrastructure requirements associated with growing boronia for oil/extract production are general farm equipment to maintain the plantation area, such as a tractor (high clearance once the crop is about 3 years old), mower/slasher and pruning equipment.

Mechanical aids and mechanical harvesters are available, though the purchase of this equipment will be determined by the size of the plantation and feasibility of using contract services rather than purchasing equipment.

Many factors influence the productivity of boronia including local climate, plant genotype, fertilisers, method of irrigation and pest and disease incidence. Plants will generally flower 12–15 months after planting and may yield 8–12 stems per plant. Commercially, plants of B. megastigma can be productive for 5 to 8 years although exceptional examples lasting up to 15 years have been experienced.

Boronia flowers in spring and is harvested when 80% of the buds are open. The flowers are combed off the plants by hand or machine. Prototype mechanical harvesters have been developed by several commercial producers. It should be noted that very strict requirements are placed on the level of leaf matter mixed with the flowers as the leaves contain waxes, which alter the composition of the oil extracted. Once the heat has been removed from the harvested flowers by refrigeration, the flowers can be stored at -18°C for a period of time before the oil is extracted.

The majority of boronia oil/extract produced in Australia is produced under contract to one major company. Most of the Australian production of boronia concrete and absolute is exported, mainly to Europe and the United States.

Risks/challenges

Boronia can be quite difficult to produce, it is prone to root diseases and rust can decimate a plantation.

The extraction method for boronia flowers is more complicated than for other essential oil crops and expert advice should be sought before establishing an extraction facility. Alternatively a contract extraction arrangement could be found to process harvested product.

The markets for boronia oil/extract are highly specialised and growers are recommended to seek contracts before considering producing the crop.

Regulatory considerations

There are regulations imposed throughout the value chain for boronia oil/extract production. For example:

• Establishment of an extraction plant requires the appropriate permits from the local government in the shire or region where the building application is being sought.
• Operating an extraction system based on solvent extraction requires expertise and the appropriate permits.
• There is no formal standard for either boronia concrete or boronia absolute.

Publications/information

Emerging Animal and Plant Industries – Their Value to Australia (2nd Edition), RIRDC Publication (2009)

New Crop Industries Handbook, RIRDC Publication (2004)

Methodology and viability Boronia Megastigma Plantations, RIRDC Publication (2002)

Boronia extracts – increasing yield and quality, RIRDC Publication (2000)

The Essential Oils Producers Association of Australia promotes and facilitates the production of essential oils and allied products in Australia