Form: Tree.

Lifespan: 50-150 years, with highest productivity in the first 40-60 years.

Leaf retention: Evergreen.

Growth rate: Slow to moderate to rapid depending on the cultivar and its environment.

Mature Size: 30-40' (9-12m) high and 15-20' (4.5-6m) wide without a dwarfing rootstock.

Flowers: Small pink flowers, fragrant, on short stalks, clustered along a stem 6-18" (15-46cm) long.

Bloom: Spring. The tree may flower several times in favorable conditions.

Self-fruitful: 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.

Fruit: 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.

Leaves: Green, long and narrow, with spiny, wavy edges, in clusters of four leaflets. New leaves are pinkish bronze. This tree provides moderate shade.

Stems: The branches are brittle and easily damaged in strong winds, especially when laden with nuts.

Roots: 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.

Wildlife: 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: No.

Origin: Australia.

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 (-5.5°C).

Chill hours: None.

Heat tolerant: In temperatures over 80°F (27°C), afternoon shade and more frequent deep watering are required. The tree is severely stressed over 100°F (38°C) and may need all day part shade.

Drought tolerant: 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.

Sun: Full morning sun with afternoon shade in regions with high temperatures.

Planting: 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' (6-7.5m) away from other plants.

Soil: 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 salt tolerance.

Fertilize: Use an organic fertilizer every 2-3 months, but not after early fall 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: Deep water 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 green veins. Macadamia trees need slightly less water than large citrus trees. They use an estimated 688 gallons (2600 liters) of water to produce one pound of nuts, more than carob but less than walnut.

Mulch: Use mulch, keeping it 8-12" (20-30cm) 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: Prune to develop a single central trunk with horizontal side branches. Flowers occur on old wood.

Litter: Dry fruit.

Propagation: 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.

Uses: 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 species.

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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