Macadamia

Siting: Macadamia trees want full sun and a humus-rich, moist, well-drained loam or sandy loam with a pH between 5.0 and 5.5; heavy clays and frost are both to be avoided. Because the wood is brittle, a site sheltered from strong wind is important, and in colder climates the tree can be grown in a container and brought under glass for winter.

Transplanting: Young trees are set out in spring or fall into holes about 45 cm deep and 60 cm across, backfilled with a mix of soil, compost and rock phosphate, then watered and staked against wind damage. In plantations, spacing runs 4 to 8 m within a row and 7 to 11 m between rows, chosen according to soil and rainfall.

Watering: Young trees need steady moisture, roughly equivalent to the 50 inches of annual rainfall found in their native range, but established trees become drought tolerant.

Feeding and pruning: Animal manure and organic mulch are applied liberally during the first four years, after which manure is reduced to avoid excess nitrogen and a resulting potassium deficiency; mulch is best spread after harvest and kept clear of the trunk. Vigorous young growth is encouraged by clipping the leading shoot once it reaches about 80 cm to promote branching, while mature trees are pruned in spring to remove old, unproductive, or diseased wood along with any nuts left on the tree.

Macadamia trees can be affected by fungal pathogens that cause flower blight, as well as anthracnose. Commercial growers must monitor and manage pests and diseases regularly to protect nut quality, though in some regions, such as Florida, few pests or diseases have been reported.

Harvest: Nuts are gathered after they fall to the ground, typically every one to two weeks during the nut season, using hand collection or mechanical sweepers in large orchards. Grafted trees begin bearing about three years after planting, though a commercially significant crop does not arrive until the seventh year, with peak yields reached after 15 to 20 years.

Storage: Fallen nuts should not sit in their husks for more than a day; husking immediately and air-drying, or delivering them to a processor the next day, helps avoid losses to mold, germination, and animal damage. When immediate husking isn't possible, in-husk nuts can be spread on a wire or slotted rack out of the rain in direct sun to dry.

Culinary: The kernels are eaten raw or roasted as a snack food, ground into flour, and used in baked goods, confectionery, and ice cream.

Cosmetic and industrial: Oil pressed from the kernels is valued for its rich, cushiony feel and oxidative stability, making it suitable for skin creams and soaps, while the leftover press cake is fed to livestock. The tough shells are put to further use as mulch, fuel, a growing medium for anthurium cultivation, a sandblasting abrasive, and in plastic manufacture, and the husks are composted as mulch.

Ornamental: Beyond the nut harvest, the tree's fragrant flowers and dense evergreen canopy also make it valued as a shade and flowering ornamental that attracts bees and other pollinators.

Cultural: The nut was an important bushfood for Aboriginal peoples in its native Australia before commercial cultivation began.

Macadamia originates in the coastal rainforests of southeastern Queensland and northeastern New South Wales, where it was gathered as a bushfood by Aboriginal peoples long before cultivation began. Seeds were carried to Hawaii in the 1880s, and though a plantation had already been established in Australia by 1888, it was the University of Hawaii's development of the crop in the 1930s that turned macadamia into a commercial success, prompting other countries to begin plantings from the 1950s onward, with cultivation expanding rapidly worldwide after 1970.