A member of the Proteaceae family, the Macadamia genus has five species. Two are grown
commercially for nuts. Macadamia tetraphylla, Rough-Shelled Macadamia, often chosen
for residential gardens because of its larger nut and higher sugar content, is described
below. Macadamia integrifolia, Smooth-Shelled Macadamia, is preferred commercially because
its smaller nuts have lower oil and sugar variability. New cultivars and hybrids between
the two often become available.
50-150 years, with highest productivity in the first 40-60 years.
Slow to moderate to rapid depending on the cultivar and its environment.
30-40' high and 15-20' wide without a dwarfing rootstock.
Small pink flowers, fragrant, on short stalks, clustered along a stem 6-18" long.
Spring. The tree may flower several times in favorable conditions.
Yes. Cross-pollination with a second plant can improve yield. Hand pollination may be necessary
if bees are not available.
Years before fruiting:
For grafted trees and cuttings, 4-8 years, with full production being reached at 10 years.
For seedlings, fruiting occurs after 8-12 years.
A fleshy green husk covers a hard woody shell containing an edible seed commonly called a
nut. The shells, very difficult to open, usually have a pebbled surface which can be smooth
in some cultivars. The nuts have a slightly higher sugar content and lower oil content in
this species, making them better for eating. After roasting, the nuts will vary in color
due to their inconsistent oil and sugar content. Macadamias have a higher fat and lower
protein content than most other commonly consumed nuts and have higher levels of
monounsaturated oil than any other food source.
Months for fruit to ripen:
7. The nuts are ripe when the husk is dry and begins to split, and when the shell inside
the husk is brown and not white. Some cultivars will drop ripe nuts on the ground for easy
retrieval which is the method favored by commercial orchards. Crushed volcanic rock or
another porous surface, which stays dry on top in a rain, can be spread under the canopy
for the nuts to land on. With most cultivars, the nuts do not ripen all at once and the
tree must be visited daily once nuts start to ripen to prevent damage due to water or mold.
Storage after harvest:
Remove husks immediately and place the shells on a screen. Air dry the shells for 2-3 weeks
in a dry, cool location. This allows the kernel inside to detach from the shell. Use a
special nutcracker to open the shell and remove the kernel. If the shell does not crack with
a clean break, it is not sufficiently dry. Dry the kernel in a food dehydrator for about two
days. The dried, raw kernels can be kept in an airtight container away from heat and light
for two weeks. They may be frozen, shelled or unshelled, for up to two years.
Green, long and narrow, with spiny, wavy edges, in clusters of four leaflets. New leaves
are pinkish bronze. This tree provides moderate shade.
The branches are brittle and easily damaged in strong winds, especially when laden with nuts.
Nursery trees may be grafted onto rootstock or grown from cuttings. The roots tend to be wide
and densely packed. Transplanted young trees have a tendency be blown over in strong winds.
Cultivars of Note:
A wide assortment of cultivars is available online, including semi-dwarf and those growing to
full size. Some have larger nuts, some are easier to dehusk and crack, others handle dry
conditions better or need cooler temperatures, still others tend to drop all their nuts
within a short time period. Avoid dwarf cultivars because of their small pea-size kernels.
The flowers attract bees. The fruit attracts various animals that make off with the nuts but
are unable to open them, leaving them to sprout in random locations.
Toxic / Danger:
Cultivation and Uses
USDA hardiness zones:
9b-12. Young plants are severely damaged in temperatures below freezing and must be protected
for the first five years. Mature trees may withstand temperatures to 22°F.
In temperatures over 80°F, afternoon shade and more frequent deep watering are required.
The tree is severely stressed over 100° and may need all day part shade.
This tree is not drought tolerant in the first five or six years. When the tree is mature, it
can withstand some drought but with the loss of its food crop.
Full morning sun with afternoon shade in regions with high temperatures.
Plant in late winter or spring after the danger of frost has passed. Locate the tree where it
can have deciduous afternoon shade and is protected from strong winds. Avoid low spots in the
yard where cold air collects. This tree must be spaced 20-25' away from other plants.
The soil must be well-draining to prevent root rot. This tree will suffer from micronutrient
deficiencies in alkaline soil, but is somewhat tolerant of soil types otherwise. Its has low
Use an organic fertilizer every 2-3 months, but not after September to avoid possible frost
damage in regions with freezes. Add a plant micronutrient solution containing chelated iron
to irrigation water three times a year. Avoid chemical fertilizers and fertilizer containing
more than 3% nitrogen, or any phosphorous, because native Australian soils, where macadamias
evolved, are low in these nutrients and the trees are very sensitive to them.
Water after becoming established:
according to a citrus watering
schedule, increasing water frequency as temperatures rise. Insufficient water is signaled by
dropping fruit. Overwatering is signaled by iron deficiency, seen as leaf yellowing between
Macadamia trees need slightly less water than large citrus trees. They use an estimated 688
gallons of water to produce one pound of nuts, more than carob but less than walnut.
Use mulch, keeping it 8-12" away from the trunk, to reduce water evaporation and soil
surface temperatures. Organic mulch is commonly used, although crushed volcanic rock may
be used in Hawaii because it also aids harvesting.
First Five Years' Care:
Protect from freezing. Always provide regular deep irrigation and afternoon shade except in
winter. Do not fertilize for the first six months in the ground.
Prune to develop a single central trunk with horizontal side branches. Flowers occur on old
Cuttings grafted onto seedling rootstock, rooted cuttings, seed. Seedlings produce a deep
taproot, if not transplanted, that anchors the tree better in strong winds and may provide
better drought resilience. Seed, however, often does not grow true to its parent,
so a seedling is best used as in-place rootstock for grafting. Rooted cuttings have a
shallower root system.
Food crop, ornamental, shade.
There is a difference of opinion over which species of Macadamia handles
temperature extremes better. Because improved cultivars have been developed, some of which
are hybrids, the choice for best temperature tolerance should be based on cultivar, not
Hawaii pioneered the commercial cultivation of macadamia nuts. The largest
commercial producers of macadamia nuts today are Australia, South Africa, and Hawaii.
Cultivated varieties are successfully grown in parts of the world that must be more than
15° from the equator.
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