A perfect climate
The eastern slopes of the Great Dividing Range in southern Queensland and northern NSW are the native habitat of the macadamia tree. This area provides the perfect conditions for macadamias to flourish – deep, well drained soil rich in organic matter, high rainfall and a warm climate with minimal summer and winter temperature variation.
Best results from macadamias are achieved at temperatures between 20° and 25°c. Ground temperatures less than -1°c can severely affect young trees and frosts of -6°c will kill young trees and damage flowers and foliage of older trees. Prolonged exposure to over 35°c will also cause stress.
Average annual rainfall should be at least 1200mm, otherwise irrigation is required. Between 1500mm and 2500mm is ideal for most soils. In some areas the volcanic rock soils of Hawaii are soaked with 4000mm p.a. which would be unworkable in Australian soils. Prolonged wet periods can cause trunk canker and blossom blight.
Commercial growers look for well drained topsoil about 1 metre deep to a minimum 0.5m. Macadamias will flourish in a wide variety of soils but with an aversion to heavy clay soil.
The establishment of a contemporary orchard is highly scientific with research and information gathered by relevant government departments, the Australian Macadamia Society, Horticulture Australia, processors, growers and plant breeders.
Many things must be considered such as location, slope, soil depth and structure, variety selection, orchard design, windbreaks, contour drainage, access, grass cover, harvesting methods and so on.
Macadamias are planted in rows from 7 to 10m apart with 4 to 5m between trees depending on the variety. This creates a density of between 200 – 350 trees per hectare.
There are around a dozen varieties of M.integrifolia in common use, developed for different fruiting seasons, disease tolerance, hardiness, quality and yield. Strong winds can retard growth, flower set and yield and may even destroy trees. Some varieties are more brittle than others, so choosing the most suitable varieties for the location is very important.
Most orchards are planted with grafted or budded trees.
Macadamias are particularly difficult to graft and it was not until the mid-twentieth century that Queensland farmer, Norman Greber, after many failed attempts, successfully grafted M.integrifolia using a simple side graft.
In today’s nurseries the whip-graft is more commonly used. Generally, M.integrifolia is grafted onto M.tetraphylla rootstock.
Grafted trees account for the bulk of nursery stock, but some breeders use a technique known as budding. This is faster and does not damage rootstock if unsuccessful, but is more difficult and more sensitive to weather conditions. For punch-budding, a special tool is used to make precise incisions. Both techniques are employed to improve the rate of growth and to increase nut production.
Seedlings are easy to germinate. When they reach 5cm in height and have two or more leaves they are potted into plastic bags. However, very few plantations breed their own plants, preferring instead to obtain their supply from specialist macadamia or fruit tree nurseries.
The priority for a young orchard is to establish robust, healthy trees. Once the trees start bearing the management strategy changes to one where the goals are to maximise the growth of quality nuts, minimise the growth of vegetation, control diseases and pests, and maintain a healthy root system.
Tree plantings in frost free areas are best carried out in Autumn. Young orchards need nurturing and are susceptible to weed competition, but until mechanical harvesting begins mulching and animal manure can be used.
First rate trees conform to a rigid crop cycle of leaf growth, flowering, nut growth and nut drop. All farming operations endeavour to be in harmony with this cycle. Soil and leaf analysis are essential tools in a high standard orchard. Other essentials include record keeping of varieties, planting dates, weather patterns, fertiliser programs, pest and disease control monitoring, harvesting yields and post-harvest testing for quality.
Macadamia growers must be prepared for many years of capital investment before any returns are possible. Establishment of an orchard requires thousands of dollars per hectare for grafted trees, planting, machinery, labour, maintenance and so on.
It takes five years until the first harvest and at least eight years for the orchard to begin making a profit. This can mean eleven years or more before the cost of the initial investment is recovered.
Pests and diseases
As with most monoculture farming, pests and diseases are a major problem. Macadamia plantations in Australia have adopted a strategy known as Integrated Pest Management. IPM combines biological, chemical, physical and cultural forms of pest suppression.
Since the introduction of IPM, use of chemical sprays has more than halved and timing of spraying has improved. Plantations not only suffer from attacks by bugs, beetles, borers, coccid, canker, caterpillars and other tiny creatures but also from rats, feral pigs, wallabies and hares. The black rat (rattus rattus) is the most destructive and can gnaw a hole in the hard shell of a macadamia in seconds. Removing feeding, habitat and nesting options for the rats is the main control strategy.
An increasing demand for organically grown produce led Mike and Liz O’Shea to convert their northern NSW orchard to bio-dynamic methods. Initially the changeover caused problems until the trees had settled into the new regime. Some minor difficulties persist, but the orchard is now commercially viable.
Harvesting begins in February/March, depending on the variety, when nuts begin to drop. Prior to mechanical harvesting, the area beneath the trees is cleared of weeds and stones and an even soil surface is prepared. Harvesting occurs every 4 - 6 weeks until September.
Various harvesting methods have been tried, but the clever ‘pin-wheel’ harvester is now the most common on use. Some harvesting is carried out on varieties with ‘sticktight’ nuts before they drop. A mat is spread under the tree which is shaken or knocked to drop the nuts.
In the fifth year one tree will bear approximately 1 kg of nuts-in-shell (NIS). After twelve years the yield is about 15 kg at which time trees may have to be thinned, thus reducing the per hectare yield. Once established and profitable, a well managed, healthy orchard could have an infinite lifespan.
Dehusking takes place within 24 hours of harvesting to prevent damage from overheating of the moist nuts. Foreign matter and inferior nuts are removed. Larger orchards use flotation tanks where immature or degraded nuts float and are discarded. To avoid rancidity, nuts-in-shell are then dried to about 10% moisture content in silos fed with forced air, before consigning to the processor. The discarded husks are recycled as mulch.