Macademia (Macadamia integrifolia) is a broadleaf evergreen prized for its nuts. Indigenous to Australia, macadamia nuts have been an important food source for aboriginal Australians for thousands of years. The tree made its way to Hawaii in 1837. The shells are so hard that ordinary handheld nutcrackers can’t open them, and commercial growers use powerful husking machines to crack them.
I. Appearance and Characteristics
Macadamia integrifolia is a small to medium-sized tree, growing to 15 metres in height. Native to rainforests in south east Queensland and northern New South Wales, Australia. Common names include macadamia, smooth-shelled macadamia, bush nut, Queensland nut, Bauple nut and nut oak.
Macadamia integrifolia leaves are simple, oblong in shape, glossy, entire with wavy leaf margins and are 20 cm long and 10 cm wide. The flowers are white or pink followed by woody, edible rounded fruits which are 2 to 3.5 cm in diameter.
This tree is rarely cultivated for ornamental purposes.
It has been introduced to Mexico and has done well in the states of Michoacán and Jalisco.
The trees will survive in hardiness zones 10 and 11.
The trees in Australia can be affected by a fungal pathogens from the Neopestalotiopsis genus and the Pestalotiopsis genus (both are within Sporocadaceae family), they both cause flower blight.
Macademia is an edible nut with no known toxicity levels except in a small percentage of people with a natural allergy to them. Allergic symptoms can include red patches on the skin, often on the back, neck, face, and between fingers, and toes. Severe allergic reactions are shortness of breath and throat swelling. If left untreated, airways may close leading to eventual death. Eating too many nuts can cause bloating, gas, and diarrhea. The nuts contain phytates and tannins which are difficult to digest.
II. How to Grow and Care
Sunlight
Macademia thrives under full sun conditions where it can receive unfiltered sunlight for at least 6-8 hours per day. This exposure is crucial for the plant’s health and productivity, especially for flower and fruit development. While macademia can tolerate some variations in light intensity, prolonged shade or low light can hinder its growth, leading to reduced yield and possibly affecting nut quality. Outdoors, macademia should be planted in locations where it can bask in the maximum amount of sunlight without obstruction. Unlike many other plants, macademia does not typically present significant adaptive traits in relation to light exposure, such as leaf adjustments or color changes, emphasizing the importance of meeting its light requirements for optimal growth.
Temperature
Macademia is quite resilient, tolerating temperature ranges from approximately 0°C (32°F) to 43°C (109°F). This heat and cold tolerance helps macademia adapt to various climates but requires special care during extremes. In colder weather, macademia may show signs of frost damage, including leaf bronzing and death of young shoots, necessitating insulation or covering. In excessive heat, heat stress can manifest as leaf curling, wilting, and sunburn, requiring shade and increased watering. Understanding these tolerances ensures macademia thrives by mitigating temperature-related stress.
Watering
Macademia thrives in well-drained soils and has adapted to withstand periods of drought, indicative of its resilience. With a preference for consistent moisture without waterlogging, macademia benefits from watering once every two weeks. As an outdoor plant often cultivated in subtropical climates, macademia requires careful consideration of irrigation during its active growth phase to ensure optimal nut production.
Soil
Native to the coastal rainforests of Queensland, macademia thrives in well-draining, slightly acidic soils with a pH of 5.5-6.5. These conditions enhance nutrient uptake and plant health. The natural soil composition includes a mix of loam, sand, and clay, rich in organic matter. To mimic this, a suitable mix can include 40% garden soil, 30% sand, and 30% compost or organic matter. Ensure excellent drainage by adding perlite or coarse sand. Use balanced fertilizers during the growing season to support healthy growth. Avoid water-logging by checking soil moisture regularly.
Fertilizing
Fertilize macademia with high nitrogen fertilizers to support robust growth, enhance flowering, and boost nut yield. Apply quarterly, tailoring quantities to manufacturer’s guidelines and macademia’s size. Increase frequency during active growing seasons. Apply carefully, avoiding over-fertilization which can harm macademia. Use a balanced feed at a lower rate in dormant phases, ensuring slow-release to maintain health without stimulating excessive growth. For safe application, keep fertilizer away from macademia’s trunk and water thoroughly after application.
Pruning
Macademia is an evergreen tree best known for its edible nuts. Prune in early to late winter before new growth begins. Key techniques include removing dead, diseased, or crossing branches to improve airflow and light penetration. Thin the canopy to maintain shape and size, ensuring a strong structure. Regular pruning enhances overall health and increases yield. Focus on maintaining a balanced framework to support heavy nut production. Always use clean, sharp tools to prevent disease transmission.
Propagation
As a native to Australia, macademia is esteemed for its nutrient-rich nuts, which are also commercially significant. Starting macademia primarily involves seed propagation; however, it is worth noting that seeds don’t always breed true to type. For cultivar consistency, grafting onto rootstocks is commonplace. When sowing, fresh seeds are preferable as they possess higher germination rates. In grafting, selecting disease-free, vigorous rootstocks is key for robust growth. Special attention to soil moisture and protection from pests enhances successful establishment.
Transplanting
Ideal for transplanting macademia is the time of abundant growth, from mid to late spring into early summer, ensuring it revels in mild weather. Choose a sunny location with well-drained soil. If needed, mulch post-transplant to conserve moisture.
III. Uses and Benefits
The showy spring and summer foliage and large fruits of the macademia tree work well in tropical gardens. Because it grows in tropical locations, it thrives in moist, sunny gardens. Large trees cast shade and smaller trees can form hedges or borders. The foliage lasts year-round, adding ornamentation to gardens even through the winter.
