Revised November 2021
The macadamia nut tree is a fast-growing, medium-sized evergreen tree with heavy, dark green foliage that hails from Australia. Its leaves – which are blunt tipped, oblong, and generally a foot or more longer – develop in either whorls of twos, threes, or fours, but are rarely solitary. Macadamia flowers are small and whitish, hassled and growing on long spikes, while its nuts can ripen throughout the year, though they primarily ripen in the fall and the spring. The nut has a leathery case that is 1 inch in diameter, containing either a spherical nut or two hemisphere nuts. They also have a smooth hard shell that encases a white kernel.
While macadamia nuts originate and are grown in Australia, commercial production is mainly in Hawaii. Some countries in Latin America, Africa, and Asia also grow macadamia nuts, while trees can be found in California and Florida for the continental United States.
The highest quality macadamia kernels are not only free of defects or insect and fungal damage, but also contain at least 72 percent oil. The kernels with less than 72 percent oil are usually immature and harder and will over-brown when roasted.
In Hawaii, commercial macadamia nut orchards are planted with grafted seedlings. Generally, the trees are at their most vulnerable during the first four years after tree establishment, after which the rows can grow together for a continuous canopy that makes the trees less prone to damage. After that, trees are likely to bear a small crop in the fifth year after planting and will reach full production in 12 to 15 years. A good tree can produce macadamia nuts for 40 years.
They prefer deep, well-drained soils that have a pH of 5.0 to 6.5, and require 60 to 120 inches of rainfall per year. They can be grown from sea level to an elevation of 2,500 feet. Macadamia trees have lower nut yields than other nut trees, meaning that it can take a while to start and maintain a positive cash flow. Because of this and harvesting expenses, macadamia orchards generally require a major capital investment.
The trees prefer subtropical climates, though too much humidity can increase the risk of blossom blights. Temperatures should not fall below -1 degree Celsius or regularly rise above 35 degrees Celsius, since the low temperatures increase the risk of damage while the high temperatures reduce vegetative growth, increases premature nut drop, decreases nut growth and oil accumulation, and may cause leaf burn.
Since they have only limited heat, frost, wind, drought, fire, and poor drainage resistance, finding a farm block of workable size for the macadamia trees can be difficult. In addition, blocks that have steep (more than 15 percent incline) or broken terrain will be more expensive to produce and manage, while blocks in drier areas (less than 1200 millimeters/47.25 inches of annual rainfall) will require irrigation. Strong wind is also a major concern for macadamia nut trees, because it can cause severe tree loss. However, narrow profile cultivars such as Kau and Pahala are more wind resistant than others.
Macadamia trees need a lot of management for profit and good nut quality. Because they are susceptible to many pests and diseases, they require regular monitoring and control measure applications. Orchard operations are also required to minimize environmental risk, due to increasing scrutiny, which means that issues such as noise pollution from de-husking, spray drift control, and soil erosion from high rainfall, shade, and mechanical harvesting need to be addressed.
Macadamia yields vary with location, season, variety, and management level. A well-managed orchard with tree spacings of 8 meters by 4 meters (or 312 trees per hectare) is expected to yield a peak of 3.5 to 4 tons of in-shell nuts per ha (12 to 13 kilograms per tree) at maturity, though poorly managed orchards or those on poor sites may not reach these figures.
Interplanting two cultivars of macadamia, such as cultivars 344 and 660, helps to improve yield through cross-pollination. Intercropping macadamia nuts with more quickly bearing crops is also a way to generate early returns. For example, in the Kona district on the big island of Hawaii, coffee is sometimes grown between macadamia nut trees.
Fertilization needs can be determined by semiannual leaf tissue analysis if it is possible. If the orchard appears normal, one sample collected before new leaf growth (February or March) or before fertilization (September or October) per tree should be enough. The branches for leaf tissue analysis should have a bud at the tip that is just opening and beginning to grow. They should not be branches with false flush buds, which have long, hard red scales and will not open for months.
Fifteen leaves from four to five trees are needed for each sample for analysis. The samples should be placed in plastic bags and labeled with name, date of sampling, and sample number.
Poorer land in Hawaii yields around 5,200 pounds per acre, while better land can yield at least 7,000 pounds per acre. In Australia, good orchards will yield around 4,000 to 5,000 pounds per acre.
Diseases that affect macadamia trees include macadamia root rot (Kretzschmaria clavis) and truck canker (Phytophthora cinnamomi). Dieback or slow decline can occur when there is trunk or root rot, soil compaction or poor drainage, poor root structure from planting root bound trees, toxic chemicals from herbicide or improper fertilizer application, or nutritional problems.
Macadamia quick decline (MQD) can also occur. While the stress factors for MQD are unknown stressors such as waterlogged soil, low pH, nutritional problems, ambrosia beetle attacks, and fungal/stem rots are suspected to be factors. Xylaria and Nectria fungi are frequently associated with MQD.
Flower blights can be caused by Phytophtora capsici or Botrytis cinerea, with Cladosporium usually as a secondary problem affecting raceme tips. While most premature nut drop is normal, environmental stress may cause excessive premature drop.
In addition to providing the nuts for harvest, macadamia trees can also help to generate honey production for nearby beehives. Sheep also can be used as natural lawn mowers to reduce the costs of herbicides and weeding, decreasing the risk of chemical toxicity in the soil and providing additional income with wool products.
Macadamia nuts are harvested manually after falling, which occurs for eight to nine months of the year in Hawaii (July to March). On relatively even land, large-scale producers use mechanical sweepers and pickup devices to offset the high cost of agricultural labor. CTAHR has developed a tractor-mounted pickup device that works for smaller orchards. To prevent losses from mold, germination, and animal damage, macadamia nuts should be harvested at least every four weeks during rainy weather, though they don’t need to be harvested as frequently during dry weather.
Unhusked nuts should not be stored for more than a day. Rather, it is best to husk the nuts immediately and either air dry them or take them to the processor the next day. In cases where the nuts were picked and cannot be husked or deliver to the processor, the in-husk nuts should be dried, by spreading them on a wire or slotted rack that is out of the rain and in direct sunlight.
While the shell accounts for most of the macadamia nut’s weight, with Hawaii’s average kernel recovery rate being around 23.5 percent during 1989-1990, an improved cracking system, along with better shell-kernel separators and high kernel cultivars, could raise the recovery rate to 35 percent.
In 1988-1999, 49 million pounds of gross, wet, in-shell nuts were delivered to processors and 3.5 million pounds (7.1 percent of the gross) were culled. This was primarily because of mold and rot, immature nuts, stink bugs, germinating nuts, koi seed worm (Cryptophlebia illepida), and the macadamia shot hole borer (Hypothenemus obscurus)
Prices paid by processors vary depending on world market forces of supply and demand, as well as Australia’s exchange rate. From 1990 to 2003, prices for in-shell nuts with 33 percent sound kernel recovery, 3.5 percent unsound kernel recovery max, and 10 percent moisture content ranged from $1.60 to $3.20 per kilogram.
Cost of Production
Before macadamia trees start to bear fruit, it can cost around $3,000 to $3,500 per hectare per year to operate a 312 tree per hectare orchard, making each tree around $10 to $12. This includes fertilization, irrigation, mulching, pest/disease/weed control, tree training, machinery operation, and labor costs. With harvesting, mechanical harvesting, de-husking, drying, and storing costs are generally around $1,000 to $1,500 per hectare, if there is a yield of 3,500 kilograms in-shell nuts per hectare. As a result, annual production costs for a mature orchard are around $4000-5000.
Significant income shouldn’t be expected until the sixth year, when the trees are mature and costs generally exceed income until the eighth year. Accumulated costs generally exceed accumulated income until at least the eleventh year. At an in-shell nut price of $2.50 per kilogram, a yield of 3,500 kilogram in-shell nuts per hectare, and production costs of $4,500 per hectare, the income from mature trees should be around $4,000 to $4,500 per hectare before fixed or overhead costs are subtracted. This makes a mature, 20-hectare orchard’s income roughly $80,000 to $90,000 before fixed or overhead costs are subtracted, though these figures can vary and taxation will affect the breakeven point.
The cost of production for New South Wales Macadamia nuts in 2004 can be found at http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0010/140212/macadamia-costs-and-returns-for-northern-nsw.pdf
There are no regulations or restrictions in the market of macadamia nuts, so the prices are determined by supply and demand market forces. The largest markets for macadamia nuts exported from South Africa are the United States, Europe, and Asia.
Currently, macadamia nuts are used for confectionary, baking, ice cream, and snack food industries. Because of the oil’s rich, cushiony skin feel and high oxidative stability, it is also suitable for heavy creams and skin care formulas. Research has shown that macadamia nut consumption may significantly lower heart disease risk.
The kernel, which is the main product of the macadamia nut tree, is oil or dry roasted after the husk is removed. Oil that is extracted from the culled nuts is commonly used in soaps, sunscreens, and shampoos, while the remaining press cake can be used in animal feed. An ounce of oil-roasted macadamia nut, which is about 10 to 12 whole kernels, has 204 calories, 21.73 grams fat, 2.06 grams protein, and 3.66 grams carbohydrates, along with 13 milligrams calcium, 33 milligrams magnesium, 57 milligrams of phosphorus, 94 milligrams of potassium, and 2 milligrams of sodium.
While the kernel and oil are the main products of macadamia nuts, both the shells and the husks also have uses. Macadamia shells can be used as mulch, as fuel in macadamia nut processing, as a planting medium for anthurium cultures (flowering plants native to tropical America), for plastic manufacture, or as a sand substitute for sandblasting. Macadamia husks can be used as mulch or compost for fertilizer.