This article is only concerned with one species, the smooth-shelled variety, Macadamia integrifolia.
HISTORY AND TAXONOMY
The history of the discovery of the first macadamia and the subsequent discovery of at least nine other species, all in Australia, is still being written. There is still taxonomic confusion, or indecision, and species are probably still being shuffled around.
A German explorer, Friedreich Leichardt, discovered a new tree in Australia in 1843. It was not immediately identified or given a name until 1858 when other botanists collected additional specimens and named it after one John Macadam, a Secretary of the Philosophical Institute in Victoria, Australia. Besides M. tetraphylla and M. integrifolia, at least 4 other macadamias grow wild in Australia: M. whelanii, whose nuts are bitter and poisonous; M. praealta, whose 5-cm round fruits contains one or two nuts with a thin shell, which were once part of the aborigines' diet; and M. ternifolia and M. heyana.
Over the years, other species have been discovered in the Celebes, and New Caledonia and for the moment anyhow, ten members of the genus, members of the Protaceae family are recognized.
The macadamia may never have achieved its status as an economic crop had it not been for the innocence (or insubordination) of a horticultural assistant in the Botanic Garden at Brisbane. It seems that the Garden's director, Walter Hill, had given some nuts to his assistant to crack and then plant. He dutifully cracked and planted some of the seeds, but ate other ones, much to Hill's horror; for the aborigines had let it be known that the nuts were poisonous. When the assistant did not become ill, Hill himself tried the nut, became enthusiastic and became its first promotor. One of the trees he planted in 1858 is still thriving and still produces nuts.
The first macadamia trees were planted in Hawaii in 1882, and in 1918, 18,000 seedlings were planted as a reforestation project! The real beginning of the macadamia industry in the Islands though, begins in the 1920s and the 1926 legislative Act that exempted from taxes, lands used only for macadamia culture for 5 years. This is the sort of intelligent legislation that is needed in many of the agricultural areas of our country. The exemption from taxation of small (and we must emphasize the idea of 'small') growers who are willing to take a chance on a new and potentially valuable crop will not have any immediate impact on state or federal revenues, but could have a great and positive impact in the future.
The Proteaceae family has about 55 genera and approximately 1200 species. It is one of the most consistent families in terms of consistent characteristics. Most of the species have a 4-parted perianth, showy racemes, 4 stamens and the fruit is usually a nut. The Macadamia genus all have whorled leaves, small bisexual flowers and a fruit which is a hard, round drupe or nut.
Macadamia integrifolia, Maiden and Betche, is also known as the Queensland Nut, Australian Nut, and the smooth-shelled macadamia. It is an evergreen tree which, if grown in an isolated area, will reach a height of 60 feet and grow a canopy 50 feet wide. The petioled leaves grow in whorls of three and are coarsely dentate when young and when mature, they are stiff, obovate and vary from a few inches to 12 inches long, have a round apex and may have from 1 to 12 teeth on each side. The inflorescence is a 12-inch-long raceme which may contain from 100 to 300 flowers. The fruit is a very round drupe enclosed in a green pericarp (husk) up to 1¼" in diameter, which usually does not dehisce on the tree.
As the two main species, M. tetraphylla and M. integrifolia hybridize freely, a large number of cultivars have been developed, most of which have been given Hawaiian names such as Ikaika, Kakea, Mauka, Makai, Keaau, Keauhou, etc. Other cultivars are Elimbah, Sewell and Probert 2. Some of the many cultivars have such desirable qualities as being immune to anthracnose, wind-resistant, yielding a larger crop, etc., but for each positive feature, there are negative ones as well. Because of the ease with which these species can be hybridized and with the advances being made in genetic engineering, it is likely that a near-perfect cultivar will eventually be developed.
Seeds can be planted in order to obtain rootstock for grafting. To do this, the fruit should be collected within a few days of falling, put in a tray and dried in the shade where there is good air circulation. When the husk splits open, the nut can be removed and planted in a sterile medium, placing the nut so that the ventral suture, the slight 'crease' that runs from the hilum to the micropyle, is on its side. If you soak the seeds for a few days prior to planting, germination, which is normally 30 to 60 days, will be speeded up somewhat.
Grafting onto seedlings that are at least two years old is practiced. Such a grafted tree will take at least four more years before it bears fruit. The grafting is straightforward: the scions should be between ½ to ¾" in diameter and be taken from branches that had been girdled six to eight weeks previously. The graft itself can be either a side-wedge or a side veneer.
Air layering is much more feasible, as you can get fruit before three years. There is a physical advantage too in that the cutting obtained from the air layer can be planted deeper and additional roots will develop near the surface.
Except for two things, the macadamia is a most tolerant tree. It will continue to thrive whether there is too much or too little water, and in almost any kind of soil. What it can't stand is excessive winds or really long periods of hot, dry weather; neither condition is usual in most of our subtropical climates. Once it is established, it will tolerate temperatures down to 25°F (-3.5°C). In Hawaii there are commercial plantings as high as 2500 (800 M) and the trees are known to be productive up to 3600 feet (1200 m). In an article written for the CRFG, B.D. Spooner notes, what Mr. Arkin has observed here in South Florida, that climate is more important than soil in the growing of this tree. Whereas any type of soil seems to do, hot, dry conditions can severely limit growth and production.
The use of nutrients is something that needs to be determined by the grove owner, as the requirements will differ with the kind of soil. Generalized remarks on this subject are contradictory, though there is some agreement that nutrients during the first year can be harmful and any subsequent feeding that is necessary should be moderate.
Windbreaks are recommended, especially when the trees are young, and in the event of a very severe freeze, protective measures such as wrapping and insulating the trunks of very young trees should be taken.
In California, trees are planted 18' apart; in Hawaii from 30 to 36' apart. Harvesting, which can be done over a period of several months, is done from the ground. Various methods have been devised to simplify this process and 'catch' the nuts before they are mixed with fallen leaves and other debris, but none are very efficient. It is a job that simply must be done every day. The home grower should remove the husks and put the nuts in a tray with a screen bottom and let them dry out of the sun for two or three weeks. The nuts are dry when they are loose in their shell. The nuts can then be stored in plastic bags to prevent them from absorbing moisture, until they are ready to be used. For the commercial processing of the nuts, see the chapter on macadamias in Rosengarten's book listed below.
DISEASES AND PESTS
A variety of insects such as thrips, mites, aphids, white flies and mealy bugs have a taste for the macadamia tree, but seemingly not to the point that major control measures are called for. Those trees with an open micropyle are subject to anthracnose and an IFAS Fruits Crop Fact Sheet notes that Phytophthora cinnamoni can produce a trunk canker which could be fatal to seedlings.
Squirrels can be a serious problem. Of the two solutions I read, one is facetious: fill'em up on walnuts so they leave the macadamias alone; and the other is practical - get a dog to patrol the grove.
The kernels of M. integrifolia contain 72% oil and 4% sugar; those of M. tetraphylla have a lower percentage of oil: 67.5 - 72% and a higher percentage of sugar: 6 to 8%. The nuts, which are still a gourmet item because of their price and scarcity, can be eaten raw, roasted or they are used as ingredients in cakes, confections and as part of such main dishes as Nutted Veal Steaks and Chicken Kiev Macadamia.
As the macadamias are self-pollinating, a backyard grower can put in a single tree to "...enjoy this rare delight, a very beautiful, delicate, white and lightly-aromatic bloom comes on early in spring. Six or seven months after bloom, one will harvest a fine cluster of fresh nuts."
1. Riley, John M., "Wild Fruits of Australia" in California Rare Fruit Growers Yearbook, 1982, p73.
2. See especially Thompson, Paul H., "The Macadamia in California" in California Rare Fruit Growers Yearbook, 1980, pp46-109. This article is tantamount to a monograph on the subject and covers every aspect of its propagation, cultivation, harvesting etc. Although written from the southern California point-of-view, it gives due notice to other practices and would prove of inestimable value to anyone contemplating a new grove.
3. Rosengarten, F., Jr., The Book of Edible Nuts, Walker & Co., NY, pp120-121.
4. Macadamias were introduced into California in 1882. According to Rosengarten there were about 800 acres of the rough-shelled variety in groves in 1984.
5. Mention planting seeds to raise them for their fruit and people look at you as if you had gone mad. "Don't you know," they say, "The seeds of most fruit trees don't come true to their parents?" Yes I do know that, but I also know that almost every major variety of tropical fruit is the result of a seedling, and not of crossings. The commercial grove owner may be obligated to utilize vegetatively propagated stock, but he or she would be foolish not to plant one or two seeds a year, especially from a prolific bearer, whether it be a mango or a macadamia, and see what develops. There is always room to plant them for ornamental purposes until they show what was hidden inside their embryo. Such a procedure should be incumbent upon every Rare Fruit Council member.
6. Perhaps one of our readers (you) would write a piece on "The Effect of Altitude on the Propagation and Cultivation of Fruit Trees and Other Plants" - or some such title. The fact is, the word 'altitude' is used as if everyone understands perfectly well the factors inherent in it that affect plant growth. I admit, I don't. Is it used as a metaphor for climate or weather conditions - it is colder, the higher up you go? Does the decrease in atmospheric pressure or the change in the chemical composition of the air have an effect on plant growth? And what about the effect of gravity on a plant at different altitudes? There is probably a difference in the amount of solar radiation received by the plants and certainly a difference in the evapotranspiration rates. Information or comments, whether in the form of notes, articles or letters would be very welcome.
7. Spooner, B.D., "The Selection of Sites for the Growing of Macadamia Trees" in California Rare Fruit Growers Yearbook, 1983, pp44-46.
8. Malo, S.W. and C.W. Campbell, "The Macadamia", Florida Coop. Extension Service, Fruit Crop Fact Sheet FC-9.
9. Arkin, Morris, "The Macadamia" in Tropical Fruit News, Jan. 1984, pp3-7. See also the same magazine, Feb. 1988, p16 and June 1989 pp55-56,60.
10. Bush, Rick, "Macadamia Nuts, a rich crop for the rich coast", in Florida Agriculture May 1, 1990. This refers to Costa Rica. An abbreviated version of the article was printed in Coccoloba, May 1990, pp6-7.
11. Endt, D. J. W., "The Macadamia Nut, A New Orchard Crop for New Zealand", The Orchardist of New Zealand, May 1975.
The 'Papershell' macadamia is a name coined by Morris Arkin to describe the thinner shell obtained from a seedling of Macadamia integrifolia. It has all the qualities of a fine macadamia nut plus the advantages of easier opening and being comfortable in the climate of Southern Florida. A fledgling Macadamia Society is being formed while this edition is in press.
DATE: July 1991
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