Fruit Facts from
California Rare Fruit Growers, Inc.
© Copyright 1997, California Rare Fruit Growers, Inc.
Common Names: Macadamia, Australian nut, Queensland Nut.
"Smooth-shelled Macadamia" (Macadamia integrifolia Maiden &
Betche), "Rough-shelled Macadamia" (M. tetraphylla L. Johnson). Hybrid
forms exist between the two species.
Distant Affinity: Helicia nut (Athertonia diversifolia), Chilean Hazel (Gevuina avellana), Australian Rosenut (Hicksbeachia pinnatifolia).
Macadamia integrifolia is native to southeastern Queensland where it
grows in the rain forests and close to streams. M. tetraphylla is
native to southeastern Queensland and northeastern New South Wales,
growing in rain forests, in moist places and along stream banks. At the
point where the two species meet, there are types that appear to be
natural hybrids. The macadamia was introduced into Hawaii about 1881
where it was used as an ornamental and for reforestation. The Hawaii
Agricultural Experiment Station named and introduced several promising
selections in 1948, which led to the modern macadamia industry in
Hawaii. In California two seedling macadamias were planted in the early
1880's and are still standing on the Berkeley campus of the University
of California. The importation of improved and named varieties into
California from Hawaii began about 1950. Macadamias are also
commercially important in Australia, South Africa and Central America.
Macadamias are ideally suited to a mild, frost-free climate with
abundant rainfall distributed throughout the year, roughly the same
climate suitable for growing coffee. Both species, however, grow well
in the coastal areas of California, although varieties often respond
differently to a given location. Mature macadamia trees are fairly
frost hardy, tolerating temperatures as low as 24° F, but the
flower clusters are usually killed at 28° F. Young trees can be
killed by light frosts. M. tetraphylla appears to be slightly more
cold-tolerant. Consistently high summer temperatures will reduce
yields, although again M. tetraphylla shows more tolerance. When grown
in a large tub, macadamias make suitable container plants.
Macadamias are large, spreading evergreen trees reaching 30 to 40 ft.
high and almost as wide. More upright types are known and being
selected because of their suitability for closer planting. The bark is
rough but unfurrowed, brown and dark red when cut. The macadamia has
proteoid roots, dense clusters of short lateral rootlets in well
defined rows around the parent root axis. The prime function of such
roots appears to be in increasing the surface area of the root system
for maximum absorption. The vigor of seedlings appears to be related to
the degree of proteoid root development.
The two species are fairly easily distinguished by their foliage. The
leaves of M. integrifolia are 8 to 11 inches in length and occur
usually in whorls of 3. The adult leaves are entire with few spines.
New growth is pale green. The spiny, often sessile leaves of M.
tetraphylla usually appear in whorls of 4 and may grow to 20 inches
long. The new growth is bronzy pink. Growth in mature trees of both
species occurs in two flushes, in spring and midsummer. In young trees
four flushes may occur.
Flowers are borne on long narrow racemes arising from the axils of
leaves or the scars of fallen leaves. They may be borne on the new
growth if it is mature, but more often on the two, or three season's
growth preceding the most recently matured flushes. The flowers, about
1/2 inch long, are perfect but incomplete in that they have no petals,
but four petaloid sepals. M. integrifolia has creamy white flowers
borne in clusters 6 to 12 inches long, while the flowers of M.
tetraphylla are cream-colored or pink and borne in clusters up to 15
inches long. Macadamias can self-pollinate, although varieties vary
from being totally self-compatible to being almost self-sterile. Wind
pollination may play some role, but bees are apparently the major agent
in pollination. Cross-pollination by hand has been shown to increase
nut set and quality.
Macadamia nuts have a very hard seed coat enclosed in a green husk that
splits open as the nut matures. As the common name indicates, this seed
coat is smooth in the case of M. integrifolia. It holds a creamy white
kernel containing up to 80% oil and 4% sugar. When roasted it develops
a uniform color and texture. Although M. tetraphylla is often referred
to as the rough-shelled macadamia, the seed coat of some cultivars are
smooth, while others are rough and pebbled. The quality of the kernels
of M. tetraphylla are also more variable. The oil content ranges from
65% to 75% and sugar content ranges from 6% to 8%. These factors result
in variable color and texture when the the nuts are roasted under the
same conditions as those of M. integrifolia. M. tetraphylla is well
suited to the home garden, however, and has been planted for commercial
production in California.
Macadamias do best in full sun, although in hot climates partial shade
can be beneficial. Windy locations should also be avoided. The brittle
branches can be damaged by wind, especially when laden with a heavy
crop of nuts.
Macadamias will perform on a wide range of soil types from open sands
and lava rock soils to heavy clay soils, as long as the soil is well
drained. They do best, however, in deep, rich soils with a pH of 5.5 to
6.5. Macadamias will not tolerate soil or water with high salt
concentrations. In areas with low annual rainfall, leach the soil
Macadamias can withstand periods of drought, but the harvests will be
small and of low quality. Irrigation seems to be more important during
certain critical periods in the crop cycle, particularly from the time
of nut set, through nut filling and through the vegetative growth
period in midsummer. The trees should receive at least as much water as
is normally provided an avocado tree. The actual amount depends on the
soil. Young trees also have higher water requirements than mature
trees. In general it is important to water macadamias regularly and
deeply during dry periods.
Since macadamias grow slowly, they do not require large quantities of
nitrogen fertilizer. Six months after planting out the trees should
receive light applications of a balanced fertilizer such as a citrus
mix or fish emulsion which contains no more than 1% nitrogen.
Applications should be made at least twice a year. A mature tree should
receive approximately 5 pounds of citrus mix per application and young
trees proportionally less. Too much nitrogen may result in chlorosis.
Micronutrient deficiencies are common in some areas, but these can be
corrected with chelated sprays.
The object of pruning a macadamia is to form a tree with a single main
stem and a framework of horizontal branches, starting at 3 ft. above
the ground and from there at intervals of about 1-1/2 ft. In M.
integrifolia there are 3 buds in a vertical row in each of the three
leaf axils of a node. When the stem is is topped, all three upper buds
will grow straight up. Only one of them must be allowed to remain and
to continue 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 branches will flower and
fruit. This process is repeated until a good framework has been
established. Macadamias will take heavy pruning but this may
drastically reduces yields.
Frost protection is more critical for young trees than more mature
ones. While they are still on the small side, the plants can be given
the standard methods of protection, such as plastic sheeting and such
draped over a frame around the tree. As the trees get larger, they are
more difficult to cover, but they also become more tolerant of mild
Macadamias are easily grown from seed, but the seedlings may take 8 to
12 years to bear a crop and the quality of the nuts is unpredictable.
Grafting is the most common method of producing nursery trees and is
best done in spring or autumn. The wood of macadamia is hard, however,
requiring the propagator to have experience to be successful. The scion
wood is girdled some 6 to 8 weeks beforehand, the preferred wood being
healthy mature material of the previous flush. The recommended graft is
the simple whip, using material 3/8 to 5/8 inch thick. The side graft
is also successful, and tip, wedge or cleft grafting is used under
greenhouse conditions for working small seedlings up to 1 ft. high.
Budding is also possible as well as propagation from softwood cutting
and air-layering. Cutting-grown trees take some time to develop an
adequate root system and will need staking when young. Some grafted
varieties of macadamias begin bearing within 2 years, while others not
for 7 to 8 years.
Pests and Diseases:
In Australia there are a host of pests and diseases that afflict
macadamias, but in the U.S. there are few problems in home gardens.
Occasionally, thrips, mites and scale may be troublesome, and
anthracnose can infect leaves and nuts in humid climates. Canker can
also result from wounds to the tree. Macadamias are fairly resistant to
Phytophthora cinnamoni, and are sometimes used to replant avocado
orchards infected with the fungus. The roots of the macadamia do not
appear to be very attractive to gophers, but deer will browse on the
Mature macadamia nuts will fall to the ground from late fall to spring.
It is best to harvest fallen nuts, since shaking the trees to dislodge
the nuts may also bring down immature nuts. A long pole can be used to
carefully knock down mature nuts that are out of reach. A reasonably
good tree will produce 30-50 pounds of nuts at 10 years age and
gradually increase for many years.
Harvested nuts should be
dehusked and spread in a dry place protected from the sun and allowed
to dry for 2 or 3 weeks. To finish drying put the nuts in a shallow pan
and place in the oven at the lowest temperature setting (100° to
115° F) for about 12 hours. Stir occasionally and watch that the
nuts do not cook. Excessive heating will damage nut quality. Store the
nuts in a cool, dry area. A heavy plastic bag will prevent nuts from
reabsorbing moisture. When the nuts are dry, the shells can be removed
with a nutcracker. A cottage industry of sorts has developed around
designing nutcrackers that can best cope with the hard shells.
home-roast macadamia nuts, place shelled nuts (whole kernels or halves
only) in a shallow pan no more than two deep. Roast 40 to 50 minutes,
stirring occasionally. Watch carefully and remove from the oven as soon
as they start to turn tan. After roasting, the nuts store nicely,
salted or unsalted, in airtight jars at 40° to 65° F. They can
also be frozen. Macadamia nuts are excellent raw or roasted. In
addition to being a quality snack, they can be used in almost any
recipe that calls for nuts, including stuffings, fruit salads, cakes,
Macadamia nuts are considered by many to be the prime edible nut. Even
at the high prices demanded, twice that of cashews, the market remains
unfilled. This demand for macadamia nuts has spurred a flurry of
plantings in areas all over the world where macadamias will thrive.
There is a limited but significant commercial production of the nuts in
Beaumont (Dr. Beaumont)
Originated in Australia. Discovered by Dr. J. H. Beaumont. Introduced
in 1965 by the California Macadamia Society. Round, medium to large
nut, 65 to 80 per pound. Shell medium-thick, kernel 40% of nut, with a
high percentage of grade A kernels. Some nuts may split on the tree and
be ruined. Texture and flavor very good. Tree upright, ornamental. New
leaves reddish, flowers bright pink, borne on long racemes. Nuts drop
over a long period. Recommended for home gardens.
tetraphylla. Originated in Encinitas, Calif. Large nut, averaging 40
per pound. Shell thin, about 1/16 inch thick, well-filled. Kernel
averages about 34% of total nut weight, quality good. Matures in
October. Tree bears annually. Not widely planted these days. Has been
superseded by better cultivars. Also used as a rootstock.
tetraphylla. Originated on the property of William R. Cate, Malibu,
Calif. Nuts medium to large. Shell average thickness. Kernels 40% of
nut, cream colored, crisp in texture, flavor good to very good. Ripens
in late October and November continuing over a period of 6 to 8 weeks.
Tree precocious, moderately hardy, shows no alternate bearing
tendencies. The most widely adapted cultivar for commercial use in
integrifolia. Originated in Hawaii. Introduced by Rancho Nuez Nursery.
Medium-sized, uniform nuts, 7/8 to 1 inch in diameter. Kernel averages
35% of nut, oil content 75%. Tree medium-tall, upright, attractive.
Begins to bear after 5 years, self-harvesting, cold resistant. Very
productive, often yielding 65 or more pounds of nuts per year.
in Australia. Imported into California by E. Westree. Thin shells.
Kernel averages 45-50% of nut. Nuts tend to drop year-round.
integrifolia. Originated in La Habra Heights, Calif. Medium-sized,
uniform nuts, about 1 inch in diameter. Kernel averages 40 to 42% of
nut, quality high, flavor very good, oil content 75%. Tree very tall,
columnar, precocious, often producing after 2 or 3 years.
Self-harvesting. Yields more per acre than any other California
cultivar, 60 or more pounds per tree when mature.
integrifolia. Originated in Lawai Valley, Kalaheo, Kauai, Hawaii.
Medium-sized nut, averaging about 80 nuts per pound; Shell smooth,
medium brown, thin. Kernel 42-46% of nut, color light cream, quality
good. Season August to November. Tree moderately vigorous, upright,
integrifolia. Originated in Kona, Hawaii by W.B. Storey. Medium to
large nut, averaging about 54 nuts per pound. Shell very slightly
pebbled, medium-thick. Kernel 37 to 40% of nut, quality tends to vary
in different locations. Harvest season relatively short, with most of
the crop maturing within about 3 months. Tree vigorous, yields well,
extremely resistant to anthracnose.
Originated in Rancho Santa Fe, Calif. by Cliff Tanner. Small to
medium-sized nut, 3/4 to 7/8 inch in diameter. Kernel averages 46% of
weight of nut, flavor excellent, oil content 75%. Shell very thin, can
be cracked in an ordinary hand cracker. Tree medium-sized, pyramidal,
begins to bear after 3 years. Self-harvesting. Flowers pink.
Recommended for both home garden and commercial plantings.
integrifolia. Originated at the Hawaii Agricultural Experiment Station,
Waimanalo, Hawaii. Large nuts, occasionally with twin halves. Shell
relatively thick. Kernel 38-1/2% of nut, flavor good, oil content 75%.
Tree medium-sized, pyramidal, productive, begins to bear after 5 years.
Produces nuts in large clusters. Resistant to frost and disease. Grows
well in cooler climates, particularly near the ocean. Also yields good
Harry M. A History of Subtropical Fruits and Nuts in California.
University of California, Agricultural Experiment Station. 1963.
California Macadamia Society. Macadamia Nut Trees for California Gardens. Undated.
California Macadamia Society. Yearbook 1955 to date.
Facciola, Stephen. Cornucopia: a Source Book of Edible Plants. Kampong Publications, 1990. pp. 380-381.
R. A. and E. T. Fukunaga. Growing Macadamia Nuts in Hawaii. University
of Hawaii, Agricultural Experiment Station Bulletin 121. 1959.
Ortho Books. All About Citrus and Subtropical Fruits. Chevron Chemical Co. 1985. pp. 59-61.
Page, P. E., comp. Tropical Tree Fruits for Australia. Queensland Department of Primary Industries. 1984. pp. 150-160.
Rosengarten, Frederick, Jr. Book of Edible Nuts. Walker and Co. 1984.
Samson, J. A. Tropical Fruits. 2nd ed. Longman Scientific and Technical. 1986. pp. 282-284.