Macadamia integrifolia, commonly known as the Queensland walnut or smooth-shelled macadamia, is a fruit tree native to Australia, renowned for its delicious nuts. It also offers decorative evergreen foliage and charming pinkish flowers. Valued both for its fruit production and ornamental appeal, it graces gardens in the mildest winter regions. It is easily grown in pots in temperate climates to add an exotic touch to patios or conservatories. It will delight enthusiasts of unique and exotic fruit trees.
Belonging to the Proteaceae family, Macadamia integrifolia is related to Protea and Banksia. This botanical species originates from the tropical rainforests of southeastern Queensland, Australia. In the wild, it grows mainly along watercourses and in dense forest areas. Introduced to various regions worldwide, it is now cultivated in Australia, Hawaii, California, and the southern Iberian Peninsula.
This tree has a moderate growth rate, reaching a height of 10 to 15 m and spreading 6 to 10 m wide. However, when grown in pots, its growth is naturally limited by the container's restricted space. For example, potted specimens in 6-litre containers typically measure between 80 cm and 1 m in height, while those in 25-litre pots reach around 1.40 m to 1.60 m. The tree has a spreading habit with a dense, rounded crown. The leaves, arranged in whorls of three to six, are single, oblong to lanceolate in shape, usually measuring between 20 and 30 cm in length. They have a leathery texture, glossy dark green colour, and slightly wavy edges. The bark is grey-brown, relatively smooth in young specimens, becoming rougher with age. The branches are sturdy, but the tree has a relatively shallow root system, making it susceptible to strong winds.
The flowering of Macadamia occurs mainly in spring, though sporadic blooms may appear at other times of the year. The flowers, grouped in pendulous clusters called racemes, measure 8 to 15 cm in length. They are white to pinkish and emit a sweet, pleasant fragrance.
The fruits are round macadamia nuts, 2 to 3.5 cm in diameter, protected by a smooth, very hard shell covered by a green, fleshy husk. Inside, the kernel is white with a delicate taste, rich in oil—a true delicacy! Fruiting may take time for potted specimens: expect 6 to 7 years.
Cultivating the Queensland walnut is possible in open ground in southern Europe, in Mediterranean climates (frost-free), provided it receives regular watering in summer. The tree prefers well-drained, slightly acidic to neutral soil and full sun exposure. It tolerates temperatures down to 3–5°C but must be protected from frost in winter, especially when grown in pots. It is a relatively low-maintenance tree with notable disease resistance. However, like many tropical plants, it cannot tolerate waterlogged soil, so good drainage is essential.
Macadamia pairs well with other orangery plants such as mimosas, lemon trees, and orange trees. It can also be placed alongside a Mango tree, a Cycas revoluta, and a red dragon fruit to create an exotic setting around this nut-bearing tree.
