Queensland Nut Tree Culture in New Zealand

New Zealand Journal of Agriculture, Volume 81, Issue 6, 15 December 1950, Page 527

Queensland Nut Tree Culture in New Zealand

By

P. EVERETT.

Orchard

Instructor, Department of Agriculture, Auckland.

THE Queensland nut tree, which is also known as Australian nut and Macadamia nut, is a native of the coastal regions of southern Queensland and northern New South Wales. It is evergreen and grows in a compact and symmetrical shape to make an attractive specimen tree. Its height at maturity varies from 30ft. to 60ft. according to strain, situation, and climatic and soil conditions. The beauty of the tree is enhanced by the many long inflorescences and the clusters of nuts produced. The nut kernel, which is of excellent dessert

quality and is suitable for use in the production of high-grade confectionery, can be eaten fresh or roasted and lightly salted. A number of Queensland nut trees growing in Northland are producing good crops annually.

THERE are many strains of the Queensland nut, known botanically as Macadamia ternifolia F. Muell. All are evergreen, but a period of reduced growth occurs during the colder months. The growing shoots are readily injured by frost, as are the seedlings in their first and second years of growth. Older trees do not generally suffer any appreciable damage when subjected to several degrees of frost. Culture in New Zealand A few seedling trees are growing in several parts of the Auckland Province, but most are at Kerikeri in Bay of Islands County, where good crops of high-quality nuts have been produced for the past 5 years. Most of these trees began to crop when 10 to 12 years old. The leaves are mainly long and narrow and may be spiny or devoid of spines according to the strain. The inflorescences, generally 6in. to 12in. long, appear mainly between August and October, but flowering may be spread over a considerable period. Up to about 20 nuts may develop on a single raceme. Each is encased in a green husk or pericarp which splits open when the nut reaches maturity. In most strains the shell is smooth, round to slightly oval or pointed, and the average diameter is about fin. The shell is relatively thin but is extremely hard and in many cases cannot be cracked with an ordinary nutcracker. The nut kernel is rich in flavour, creamy-white, and possesses excellent keeping qualities.

Some strains of Macadamia produce nuts up to IJin. in diameter with a rough exterior and a shell which is so thick and hard that it is not readily cracked even with a hammer. Seedlings from this type have recently been raised in New Zealand, but none has yet come into bearing. .. As experience overseas indicates that trees are not readily grafted or raised from cuttings, propagation in New Zealand has so far been by raising young plants from seed. Crosspollination occurs naturally, so that seedling trees do not always possess the same characteristics as their parents. The percentage of nuts that will germinate decreases with age, but about 70 per cent, can generally be secured from freshly harvested nuts. Before planting, the pericarps (but not

the shells) should be removed and the nuts planted on their sides and covered with about IJin. of friable soil. Young seedlings normally appear above ground 30 to 40 days from the time of planting, but in some cases germination may take up to 90 days. Best results can be expected by planting the nuts in September or October. Well-grown seedlings are a suitable size for planting out when 2 or 3 years old. For commercial plantings spacing of 22 to 28ft. on the square is recommended. Diseases and Pests No diseases have been recorded as attacking the Queensland nut in New Zealand and the only insect pest observed by the author to date is a species of thrip which causes silvery markings on the foliage and husks. The green vegetable bug (N ezara viridula) is a pest of the Queensland nut in Australia, where it sucks nutrient sap from the immature nuts, causing the fruit to drop while immature, and this insect may cause similar damage in New Zealand. Thrip and the green vegetable bug can be controlled by spraying infected trees with D.D.T., using lib. of a 50 per cent, wettable powder in each 100 gallons of water. Until better-fruiting, more even types are available this ornamental and useful tree cannot be recommended for commercial planting in New Zealand. Seedling trees are considered eminently suitable in the warmer parts of the Auckland Province for planting in large private gardens, city parks and domains, and also as street trees, where overhead wires have not to be contended with. Reference “The Queensland Nut”, by J. M. Wills, “Queensland. Agricultural Journal”, June and July, 1945.