Species: "Smooth-shelled Macadamia" (Macadamia integrifolia), "Rough-shelled Macadamia" (M. tetraphylla L. Johnson). Hybrid forms exist between the two species.
Macadamia integrifolia is a native from southeastern Queensland, Australia. The tree grows in the rain forests near rivers and streams. M. tetraphylla has a native range from southeastern Queensland and northeastern New South Wales. The macadamia was introduced into Hawaii around 1881. The trees where introduced for reforestation purposes. Click here to buy Macadamia Fruit Trees
Macadamia nuts originally came from Australia and named after Dr. John Macadam, a noted scientist and secretary of the Philosophical Institute of Australia in 1857.
Hawaii leads the United States in production while here in Florida we also have some macadamia orchards as an alternative crop. These tropical trees, tolerate mild freezing (28-32 F), and do not tolerate excessive heat. Macadamia trees need some cold protection much like citrus and fig trees.
In 1948, the Hawaii Agricultural Experiment Station introduced several promising selections which led to the modern macadamia industry in Hawaii and later in California.
Adaptation: Macadamias are well adapted to a mild, frost-free climate with plenty of rainfall distributed throughout the year. Mature macadamia trees are fairly frost hardy, and can tolerate temperatures as low as 24° F. Flowers, however, are usually killed at 28° F and young trees need to be protected from frost or they may die. Macadamias can be good container trees if given a large enough planter.
Growth Habit: Macadamias are large, spreading evergreen trees that can reach 30 to 40 ft. high and with an impressive width. The tree bark is rough but unfurrowed, brownish and is dark red when cut.
Leaves: M. integrifolia has leaves approximately 8 to 11 inches in length and occur usually in whorls of three. Adult leaves are complete with few spines. New growth is a pale shade of green.
The leaves of M. tetraphylla usually appear in whorls of 4 and can grow to a length of 20 inches. These spiny, often sessile (leaves that are directly attached to the plant's base. These leaves do not depend on any stalks and are borne directly from the plant's stem since they do not have a petiole.) Mature trees of both species have leaves that occur in two flushes, in spring and midsummer. In young trees four flushes may occur. The new growth is bronzy pink
Flowers: Flowers are borne on long narrow racemes. The racemes may be borne on the new growth if it is mature, but more commonly on the two, or three season's growth following the most recent matured flushes. Macadamia flowers are about one half inch long. M. integrifolia has cream colored white flowers borne in clusters 6 to 12 inches in length. The he flowers of M. tetraphylla are cream-colored or they may be pink and develop in clusters up to 15 inches long. Macadamias can self-pollinate but this varies. Some trees are totally self-compatible and others require cross pollination. Bees are apparently the major agent in pollination. Cross-pollination by hand is often utilized and is known to increase nut yield and quality.
Nut/Fruit: Macadamia nuts are very hard. The seed coat is enclosed in a green husk that splits open as the nut matures. M. integrifolia produces a creamy white kernel containing up to 80% oil and very little sugar. When roasted it develops a uniform color and texture.
M. tetraphylla has an oil content range from 65% to 75% and almost 8 percent sugar versus the 4% of M. integgrifolia.
Location: Well suited to full sun but prefers part shade in hotter climates. Protect trees from windy locations since the brittle branches can be damaged by wind, especially when laden with a heavy crop of nuts.
Soil: Macadamias will perform on a wide range of soil types from open sands and heavy clay soils that are well drained. They do best in deep rich soils with a pH between 5.5 - 6.5. Macadamias are not salt tolerant.
Irrigation: Mature Macadamia trees withstand periods of drought. Drought conditions will yield a small low quality harvest. As it is common with fruit trees, irrigation seems to be critical during flowering and nut development. The trees should receive as much water as is provided an avocado tree. Exact amounts of irrigation depend on soil drainage, temperature etc. Young trees have higher water requirements than mature trees. Deep watering on a regular schedule during drought is extremely important in the growth, development and health of Macadamia trees.
These trees are slow growers and they do not require large quantities of nitrogen fertilizer. Young trees to one year old should be given light applications of fertilizer*. They are not heavy feeders, and their fine lateral roots are efficient in absorbing phosphorus and calcium, even where there are low levels of these nutrients in the soil.
The Trees are extremely sensitive to phosphorus, so fertilizer needs to be very low in phosphorus and some growers recommend they get none at all. We like to use Florikan 18-6-8* on our young trees. This fertilizer is high quality and it is low in Phosphorus. We find that it really gives them a good start. Too much nitrogen however may result in chlorosis. Additionally, micronutrient deficiencies are common in some areas, but these can be corrected with chelated sprays.
Pruning: Prune a macadamia to form a single main stem and a framework of horizontal branches. The horizontal branches should be about three or four feet from the ground. When a stem is topped, all three upper buds will grow straight up. Allow only one of these to remain as the main stem, the other two being clipped off to a stub of about 3/8 inch. Now the buds below those two stubs will grow out in a more or less horizontal direction. Only these horizontal branches will flower and fruit. Repeat this process to form a good framework.
Propagation: Macadamias are easily grown from seed, but the seedlings may take 8 years or more to bear a crop. Seedling trees are unpredictable as to nut quality. Seed grown trees however, offer new hybrids opportunities and the trees gene pool is improved over time. Named varieties of Macadamia trees can be propagated by air-layering or from cuttings for faster nut production. Grafted, air layered or cutting grown varieties of macadamias are difficult to source but they may begin bearing within 3 years. Arkin and Dana White are excellent varieties for Florida.
Pests and Diseases: In the U.S. there are few problems with backyard grown Macadamia trees. Thrips, mites and scale may be troublesome from time to time and leaves may be infected by anthracnose in humid climates.
Harvest: Mature macadamia nuts are best harvested from the ground. The nuts fall to the ground from fall to spring. A good 10 year old tree can produce between 25 -50 pounds of nuts and gradually increase for many years. Click here to buy Macadamia Fruit Trees