Family: PROTEACEAE
The macadamia is a small to medium, long lived, evergreen tree, which usually commences nut production between years 4 and 6. It is the first tree native to Australia which has been devel-oped into a commercial tree crop. It is hardy to about - 4°C, although light frosts can kill new foliage which has not had a chance to harden off. Heavy frost can kill small trees and reduce yields on mature trees. It is fairly drought tolerant but will produce more reliably with irrigation. The most important watering times for a good crop are spring and early summer.
Macadamias grow best in deep, fertile, well drained soils, although they often grow on the edge of water courses where the clay is less than 100 mm from the soil surface. They do not favour acid soils, which should be treated with lime or preferably dolomite. They require no more than corrective pruning. Trees are prone to losing limbs in strong winds, so sheltered sites are recommended. They tend to produce less nuts on the windward side.
The recommended spacing of trees is 9 m x 9 m. As it is many years before the trees fill this space, a secondary crop can be grown between the macadamias. Alternatively, seedling trees can be planted much closer together and selectively thinned as their production characteristics become known. A tree aged 15 years can produce up to 40 kg of nuts.
The nuts are extremely hard shelled which renders them parrot proof. They remain fresh for a couple of years. Commercially, most nuts go to the confectionery trade but increasingly the fresh nuts are being eaten out of hand.
Nutritional composition of the macadamia per 100 grams of edible portion is: Water - 3.0%, Energy - 691 calories, Carbohydrate - 15.9 g, Fat - 71.6 g, Protein - 7.8 g, Ash - 1.7 g, Calcium -48 mg, Potassium - 264 mg, Iron - 2.0 mg, Phosphorous - 161 mg, Thiamin - 0.34 mg, Riboflavin - 0.11 mg, Niacin - 1.3 mg.
There are now many grafted cultivars of macadamia available. A planting incorporating a selection of these cultivars and a dominance of seedlings is recommended to provide a greater cross - pollination and a more diverse crop. Adverse weather may reduce the production from a certain cultivar but not others, because of differing flowering times.
Interplanting young trees with nurse species such as tagasaste, small acacias and cassias will greatly reduce negative effects from wind. Small acacias can help to reduce the likelihood of root attack from Phytophthora cinnamomii which causes a trunk canker. It is advisable not to cultivate soil around macadamia trees because damaged roots are most vulnerable to this root fungus.
Propagation from seed is relatively simple. Seed is first soaked overnight in warm water. Any floating nuts can be discarded. Seeds can be planted directly into pots or the soil, but keeping them in barely damp, warm peat moss until they sprout gives the advantage of only dealing with those seed which are viable.
There are 6 known species of macadamia but the two listed are the only ones recognised to have commercial potential. The two species hybridize readily, forming trees often more productive than either parent.