Rural Industries Research & Development Corporation

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Introduction

Boronia heterophylla can produce reasonably long stems of vibrant pink flowers. Bushes are quite productive for several years. Postharvest life is adequate and there is strong export demand. The main limitations for expanding boronia production are the restricted flowering period and colour range. Boronia heterophylla is the dominant crop both domestically and for export. Unfortunately in most areas the harvest is over within two weeks.

Some varieties of B. megastigma are cultivated but the market is much smaller as the postharvest life is short and the perfume is unattractive in Asia, making it unsuitable for export. Production of other species is quite limited. Until recently B. megastigma was the only species that had been surveyed for superior varieties. New selections of B. heterophylla have recently become available and more should be released within the next few years. These varieties will offer a greater range of colour and flowering time. Also a breeding program examining a wider genetic base within the genus Boronia has begun and this should result in a range of new products. Increases in production are likely to be tied to the demand for new varieties. Access to the USA could also increase demand for Australian product and this is currently being pursued.

Boronias are currently grown for cut flowers on the east and west coasts of Australia, New Zealand, California, Israel and to a lesser extent in South Africa and Europe. They are susceptible to root rots and rust and require good site selection and careful management.

Markets

Plant selection

Boronia heterophylla is an upright shrub 2–3 m tall from Western Australia. It bears a profusion of vibrant, pink, bell-shaped flowers about 1 cm long which provide a spectacular floral display. This species is the most widely grown for cut flowers. The flowering period for individual plants is usually less than two weeks in late September/early October and flowers fade if left on the bush. Some flower colour selections have been registered including, ‘Moonglow’ (white), ‘Cameo’ (pale pink), and ‘Lipstick’ (mid-pink) and ‘Morandy Candy’ (deep pink), which may be hybrids. B. heterophylla is fast growing and responds well to pruning. It withstands light to moderate frost. Plants prefer dappled shade or partial sun but will grow well in full sun if roots are kept moist and protected.

Boronia megastigma is an upright, dense shrub 1–3 m tall. It is found in wet or seasonally wet sites in Western Australia. Individual plants flower from late July to October. The bell-like flowers are usually dark to reddish brown on the outside and yellow on the inside and are not showy. Flowers are very fragrant. B. megastigma used to be extensively grown as a cut flower in Victoria but rust (Puccinia boroniae) wiped out the industry. Selections, based on morphological characters desirable for cut flowers, include forms where the outside of the petals are red, such as ‘John Maquire’s Red’, ‘Arch Chandler’s Red’ and its sport ‘Harlequin’ which has vertical reddish-brown and yellow stripes, and ‘Lutea’ a yellow-green form. Unfortunately these selections have poor vase-life and do not transport well. The perfume, which is the main attraction in Australia, is less desirable in Asia. Much variation exists in flowering time, flower colour, fragrance, oil content and growth habit.

Boronia muelleri is from the southern coast of New South Wales and Victoria. Flowers are 1.5 cm across and vary from white to pale pink. Flowers are borne on terminal clusters from August to November. At present production is limited.

Boronia purdieana is a small shrub from Western Australia. It bears a profusion of perfumed, greenish-yellow flowers from July to August. This early flowering species has short stems (30–40 cm) but it is sought after as a cut flower. Cultivation is still limited and in 1993 there were 49,000 bush harvested stems and 900 stems from cultivation. Boronia purdieana is from the coastal sandplain north of Perth and it probably requires well drained soils and will grow in hotter/drier areas than B. heterophylla.

Boronia pinnata is a small shrub from New South Wales. It bears pink clusters of flowers from August to November. It is largely bush picked and is in demand from florists. It has 5–8 days of vase life. It is difficult to propagate.

Boronia serrata is a small shrub 1.5 m tall from New South Wales which produces abundant rose pink flowers. Individual plants produce flowers for 4–8 weeks but flowering in natural habitats occurs from late July to November. A short vegetative flush occurs from December to January and this can be extended in cultivation with irrigation. Plants produce 20–25 cm cut flower stems.

Agronomy

For cut flower production, boronia should be propagated from cuttings. This will provide uniformity in flower quality, stem length and harvest date. Choose a reputable nursery and allow at least four months between ordering and delivery. Tip cuttings are most successful when taken from new shoots over summer (Nov–May). High concentrations of auxins, basal heat and misting improve rooting. Losses through damping off can be reduced with good hygiene and by avoiding root damage. Boronia can be propagated in vitro but shoot multiplication is initially quite slow. Time for delivery will greatly depend on the availability of cultured stock material. Murashige and Skoog nutrients supplemented with benzyl amino purine (BAP at 1 µM) stimulate shoot production. Root formation can be promoted by naphthalene acetic acid (NAA at 2.5 µM) in liquid media.

Boronias require a period of cool conditions (winter nights less than 10°C) to initiate flowers. Warm conditions can lead to flower abortion at certain stages of flower development. Inadequate chilling is often seen as vegetative growth at the tips of stems and this reduces stem value. Boronias have been successfully cultivated across a range of latitudes from the hot dry conditions of Coorow, WA (30°S) to the cool temperate conditions of Tasmania (42°S) and even the South Island of New Zealand. The site should be frost free but many species are frost tolerant. Strong winds will damage shoots and weaken roots and so windy sites should be avoided or wind breaks constructed or planted.

Although some boronias naturally grow in wet areas, in cultivation they prefer well drained soils. Soils from the site should be analysed. Boronias prefer slightly acidic soils. Soils with a very high residual phosphorus level should be avoided. Sites should be tested for the presence of Phytophthora and nematodes. Phytophthora affects many Australian plants and is virtually impossible to eradicate. Also avoid sites with root attacking nematodes, such as Meloidogyne or Pratylenchus, or treat the area with a suitable soil fumigant or nematocide.

The ground should be prepared and weeds controlled before planting. Good planning at this stage is critical. Remove any large tree roots and cross rip. Remove soil from machinery before use to reduce the risk of introducing Phytophthora to the site. Plants should be ready to plant in winter to capitalise on the growth flush over spring/summer. Plants should be disease free, 10 cm high with well formed roots. Ensure plants are not root bound. Remove plants carefully and do not disturb the roots when planting.

Planting design will depend on your irrigation system, management practices and the species selected. Blocks of single or double rows of plants with roads for machinery access between blocks are the most common designs. Plants in single rows are 1.5 m apart with 0.7 m between plants with a spray row where required. Double rows with 1–4 m centres have 0.7 m between plants down the row and 0.5–1 m across the row. Rows are aligned north to south. In Western Australia the usual planting density of B. heterophylla is 7,000–10,000 plants/ha, whereas in Tasmania, densities of up to 19,500 plants/ha are used for B. megastigma.

Irrigation or reliable rainfall throughout the year is essential for successful production. Boronias are shallow rooted and B. heterophylla, for example, produces a mat of roots in the top 30 cm of soil. The soil therefore needs to be kept moist. Roots are susceptible to root rot and collar rot fungi and so should be grown in free draining and not waterlogged soils. Mature boronia plants require 2–10 litres of water/day depending on conditions. Micro-irrigation supplied several times a day is preferable.

Mulching is highly recommended due to its beneficial effects on water use, and disease and weed control. Artificial mulches include plastic mulch, weed mat and local by-products such as wood chips can be used for organic mulches. Organic mulches can substantially reduce water loss from evaporation. They also keep the roots cool which reduces plant losses from water stress and slows the growth of root rots. Composted straw and other organic mulches give some control of diseases, such as Phytophthora, by encouraging organisms antagonistic to these pathogens.

Mulching generally gives good weed control. This is particularly important in boronia as root disturbance often leads to plant death. Grasses can be controlled with systemic herbicides like Fusilade®. Broad-leaved weeds are more difficult but may be controlled with a hooded wand using a non-selective herbicide. There are no selective broad-leaved weed herbicides registered for use on boronias.

Boronias require fertiliser application, especially nitrogen. For spring flowering species, vegetative growth occurs from mid-spring to autumn with a peak over summer. Stem length is critical for profitable cut flower growing, and fertilising during the growth phase is essential. However late application of fertiliser, particularly nitrogen, can reduce flowering especially of shoot tips, and should be avoided. Fertiliser can be applied as a solid or in liquid form through fertigation. Greater control of fertiliser application is possible with fertigation and split applications are recommended for solid fertiliser to avoid plant death or nutrient loss through leaching by heavy rain. The NPK requirement will vary depending on soil type but applications of N:P:K::90:10:130 kg/ha/year have been used for B. heterophylla in Western Australia and N:P:K::50:79:100 kg/ha/year for B. megastigma in Tasmania. Trace elements should be applied in areas deficient in micronutrients. Plants should be analysed to determine any nutrient
deficiencies.

Pests and diseases

Boronias are susceptible to root diseases, especially Phytophthora and Pythium. Boronia often suddenly die and this is probably due to infection from these pathogens after wounding from insects, wind damage or water stress. Fosject® can be used to control both Phytophthora and Pythium. Rust (Puccinia boroniae) causes brown pustular growths on boronia and may cause leaf drop. Tilt®, Mancozeb® and Baycor® have been used but contact your local agronomist for suitable methods of control. Boronias are also susceptible to Botrytis and require fortnightly treatment from bud initiation to harvest, especially during wet conditions. It is better to use a rotation of fungicides, such as Rovral®, Bravo® and Octave®.

Harvest, handling and postharvest treatments

Stems should have abundant flowers for most of their length. At least 50% of flowers need to be open at harvest. Clean straight stems of B. heterophylla 60–70 cm, with 50–70% of blooms open and no wilting are regarded as first grade cut flowers by the Floral Export Council of Australia. Second grade stems are less than 60 cm but should have a minimum length of 50 cm, 50–70% of flowers open, no wilting and clean stems with no more than 5% curve. A premium is paid for >80 cm stems. Stems are bunched in fives or tens for Japan, while most other markets require the product to be sold by weight.

Without treatment, vase life is short. Standard postharvest care, including placement in clean water, removing field heat as soon as possible and storage at
1–5°C, greatly improves quality and longevity. Delays in cooling greatly reduce flower quality. Pulsing with a biocide, such as
8-hydroxyquinoline citrate (HQC, 800 mg/L) overnight
(8 hours) increases vase life. Flowers are usually provided bunched to the exporter, who handles packaging and consignment to domestic and export markets. Check requirements for handling with your exporter.

Economics of production

Harvest date will also affect value and whether part or the whole crop is given the same price. For example Victorian ‘Red’ B. heterophylla is usually harvested before Western Australian product, and the variety ‘Lipstick’ is earlier still. Product which appears on the market earlier usually obtains a better price. Prices will also depend on the air freight charged to the exporter and this is considerably higher out of Western Australia than from the eastern States. For example freight charges to Japan in 1996 were $1.40/kg from the east coast and $2.80/kg from Perth or $0.75–$1.20/bunch higher from the west coast. The responsibility for risk will also affect prices. This includes quality claims against the product and quarantine claims; on the west coast these are the exporter’s risk. A summary of prices paid by exporters to growers is presented for 1996. Be sure to check with your exporter on which charges and costs are the grower’s and which are the exporter’s as this will greatly affect your returns.
 

Key references

Growing Boronia Agriculture WA Farmnote No. 47/96 (Agdex  282/220).

Plummer, J.A. and Considine, J.A. 1997 Genetic Resources, Biology and Agronomy of Selected Boronia Species for
Production of Essential Oils and Flowers Final Report to RIRDC/HRDC. Technical Report No. 4. Plant Sciences, University of Western Australia.

Plummer, J. A. et al 1998 Selection and production of Boronia. Acta Horticulturae (in press).
 

Key contacts

Gill Lisson
Agriculture Western Australia Albany
Phone: (08) 9892 8424
Fax: (08) 9841 2707

Exporters
Collina Exports
Phone: (03) 9329 3322
Fax: (03) 9329 3366

Total Flower Exports
Phone: (08) 9451 5744
Fax: (08) 9351 8019

Sunglow Flowers
Phone: (08) 9525 1800
Fax: (08) 9351 8019

Westralian Flora Exports
Phone: (08) 9250 2431

Floratrade
Phone: (03) 9338 0444
 
 

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