Crop of the Month: Macadamia Nut

William H. Purvis, the young manager of the Pacific Sugar Mill at Kukuihaele on Hawaiʻi Island, planted the first mac nuts in 1882 at Kapulena.

By Damon Adamson.

Rows of trees in mac nut orchard.
Macadamia Nut Orchard (Macadamia integrifolia) ssp. Makai 800. Photo by Damon Adamson, click to enlarge.

Hailing from southern Queensland and northern New South Wales on the continent of Australia and belonging to the Proteaceae family, the macadamia nut (Macadamia integrifolia) was first imported into Hawaiʻi in 1882 by William H. Purvis. Purvis, the young manager of the Pacific Sugar Mill at Kukuihaele on the Big Island, planted seeds that year at Kapulena.

Though many species exist of Macadamia ssp., only two species produce kernels or nuts that are edible in their raw form: Macadamia integrifolia and Macadamia tetraphylla. Generally, both tree species grow medium to large (40-60 ft with very mature trees), produce lengthy green leaves, and make for very attractive orchard specimens.

While many traits are similar, between the two species, it is M. integrifolia that is the most important as a tree crop macadamia due to its likability and preference by individuals across the globe.

The sub-species Keaʻau (660), according to Richard A. Hamilton, professor emeritus of horticulture at the College of Tropical Agriculture and Human Resources, University of Hawaiʻi at Mānoa, was selected in 1948 and named in 1966. It has an upright growth habit, allowing somewhat closer planting than varieties with more spreading trees. Keaʻau has outstanding nut and kernel characteristics, with 42 to 46 percent kernel, more than 95 percent of its kernels are grade one. Keaʻau trees have performed well in most areas where this variety has been tested.

The singular seed, rarely double, boasts an extremely hard shell accompanied by an outer husk. The singular seed or kernel is pale in color, smooth, and circular in shape unlike M. tetraphylla, which produces slightly spindle shaped nuts.

Nutritionally, the kernel yields a powerhouse of beneficial vitamins and minerals such as significant levels of vitamin B6, manganese, iron, iron, magnesium and protein.

Additionally, like all nuts, macadamia are noted for higher fat levels.

The kernel is enclosed within a round shell usually between 0.6 to 1.1 inches in size which is enclosed in a husk outer shell. The slightly pointed leaves are medium in length (150-200mm) with a slightly undulating margin, narrow, has few spines and a long petiole.

A moderate to dense canopy can yield high production rates.

Flowers have medium to long racemes (150-200mm), are highly concentrated, and have variable timing and bunch numbers.

It is prone to early nut drop and generally tends to germinate in wetter conditions. Many commercial orchards maintain the practice of utilizing M. tetraphylla as a root-stock for propagation of M. integrifolia, though both stocks are viable.

M. tetraphylla is suggested to be preferred for its ability to germinate uniformly, grow faster, and are considered somewhat easier to graft and transplant. There is, however, a possible problem whenever M. tetraphylla seedlings are used as root-stocks for M. integrifolia varieties. The trunk of M. integrifolia varieties sometimes grows faster and increases in diameter more rapidly than the M. tetraphylla root-stock.

Happy growing…


Macadamia Integrated Pest Management: IPM of Insects and Mites Attacking Macadamia Nuts in Hawaii, Vincent P. Jones, College of Tropical Agriculture and Human Resources (CTAHR), UH Mānoa.

Macadamia, Hawaii’s Dessert Nut, Richard Hamilton, CTAHR, UH Mānoa.

Macadamia Nuts in Hawaii: History and Production, Gordon Shigeura, CTAHR, UH Mānoa.

Damon Adamson (senior, horticulture) received a bachelor of arts in history from UH West O‘ahu. He is retired U.S. Army, born in San Diego, CA.