Macadamias originated from the subtropical regions of Australia. That is the first indication of which climates are most suitable for the establishment of macadamias. In areas where avocados, papayas and bananas thrive, Macadamias should be able to produce as well. When choosing the right locality to plant macadamias, the maximum and minimum temperatures as well as the height above sea level should be taken into account and the prevalent winds.
The optimum temperatures for photosynthesis are between 25°C and 35°C. The further temperatures move out of these limits the higher the risks for economic macadamia nut production. There are a lot of areas with maximums higher and minimums lower than the ideal but every situation and locality has to be evaluated in its own right. Sometimes by applying management strategies such as planting and choosing the right facing slope, a microclimate might be found that is suitable for growing Macadamia nuts. Temperature is the major climatic variable determining macadamia growth and productivity.
Temperatures higher than 30°C for long periods of time result in the growth of distorted and chlorotic new growth (Heat stress). High temperatures at flowering will reduce fruit set, and will cause immature nut drop during early development. Although Macadamia trees can survive temperatures below 3°C, young trees can be killed by frost if the temperature gets below 5°C. There are cases reported where mature trees withstood frost at temperatures as low as 5°C for a short period.
The height above sea level influences both nut quality and the production of the trees. At altitudes above 600m, the quantity of grade one kernels as well as total nut production is reduced. Growth is slower above 650m and trees take longer to come into bearing. The higher the altitude the thicker the shell becomes. Limited observations from SAMAC cultivar trails in all Macadamia producing areas in South Africa have shown cultivar performance differences compared to Australia and Hawaii and we might find that in our climate and conditions, other varieties do better at higher elevations. In Hawaii the 294 (Purvis), 800 (Makai), and 660 (Keaau) were found to be better suited to altitudes from sea level to 300 meters. Between 300 and 650m above sea level the 741 (Mauka), 344 (Kau), and 660 (Keaau) produced well.
In all the existing production areas in South Africa the rainfall is between 800 and 1200mm per year. Although adequate, 70% falls in the summer months with periodic droughts throughout the year. Supplementary irrigation will assist in, especially the case of young trees to help bring them into production sooner.
Orchards in production can be assisted by irrigation to get through critical periods such as from the time when pollination takes place to the end of oil formation. This is September – March, when the trees are sensitive to a shortage of moisture and any irrigation in that time will assist in a better yield and growth.
Macadamia trees are prone to wind damage, although the wood is hard, it is brittle. Wind protection should be provided in the form of rows of trees that grow fast and can lessen the effect of the wind on the Macadamia trees. Casurinas are the most commonly used as effective windbreak trees.
Narrow crotch angles and multiple branches on Macadamia trees should be trained and pruned to get stronger crotch angles between the stem and the side branches during the first two to three years. This not only provides structural strength against wind damage, but also improves light penetration into the canopies, which will develop.
Most cultivars grown commercially in the world today are from selections made from the M. integrifolia specie at the Hawaiian Agricultural Experimental Station and given an HAES number. The earlier successful cultivars were also given a Native Hawaiian name. For example, HAES No 74 I, native Hawaiian name: Mauka and 788 is Pahala.
Macadamia nuts traded and consumed in the world markets today are therefore mainly a mixture of approximately 10 of these Hawaiian cultivars, whether produced in Australia, South Africa or Hawaii. Some hybrid cultivars, arising from both natural and artificial crosses between M. integrifolia and M. tetraphylla have also been selected and commercially grown in South Africa, Kenya and Australia. Although those hybrids generally produce superior yields in many of the localities from which they were selected, most have slightly different kernel characteristics in comparison to the Hawaiian cultivars. to which both the trade and consumers have become accustomed.
For any new grower wishing to establish macadamias, the cultivar choice is an extremely important one, and should only be made after wise consultation, on the basis of both yield and quality characteristics. Herewith, on the basis of all the knowledge gained from SAMAC’S cultivar research to date (oldest cultivar trial now 11 years old), some guidelines:
- Use at least 3 or 4 cultivars in any planting:
- Safest bets at present for long term performance in terms of both yield and quality, in existing growing regions:
- 788 Pahala
- 741 Mauka
- 816 unnamed
These are all cultivars of Hawaiian origin, with known excellent quality characteristics and all capable of producing average yields of at least 4 tons Dry-in-Shell nuts per hectare at maturity (±12 years onwards). In most areas these cultivars will produce their first small crop at ±5 years of age. They will also produce kernel recoveries in excess of 30%.
The more precocious cultivars, which come into commercial production at an earlier age, but whose kernel quality characteristics make them less readily acceptable in existing markets, can be considered as inter plants in high-density plantings, where they can be thinned out after 8-12 years depending on the spacing chosen. These include:
- 695 Beaumont (hybrid)
- 791 Fuji (M.integrifolia/M tetraphylla/M ternifolia, Tribred)
Note that these are general guidelines only. More precise recommendations for specific regions will become available as the information from SAMAC cultivar trials increases.
PLANTING DISTANCES AND DENSITIES
Earlier trees were planted at distances ten to twelve meters apart. But the long period for the tree to fill the spaces has brought the idea to plant closer as is the tendency with most tree crops. On this SAMAC and the ITSC launched a trial to determine the best planting distances. Out of these trials the closest planting distance of three meters in the row and five meters between the rows were determined.
Macadamias need to be fertilized from planting. Although in small quantities it must be done to ensure good growth. The trees do grow slowly and have to be helped to grow bearing wood in as short a time as possible.
- Mason RL. 1982. Macadamia nut Quality – The effect of harvesting practices. AMS Bulletin May 1982.
- Mason RL. Young G and Young K. The development of a commercial macadamia nut quality grading system.
- Final report. AMS News Bulletin. July 1996.
- The Cracker INC September 1997 – April 2000 World Consumption and Production Trends:
- McConachie. Ian. On Shoes and Ships and Macadamia Nuts. AMS News Bulletin, November 1997.
- McConachie. Ian. The Big Picture. SAMAC 1999 International Symposium.