The AMS receives lots of enquiries from new and existing growers about a variety of topics. Our most frequently asked questions have been answered in this FAQ sheet, however please feel free to contact us on FREECALL 1800 262 426 (Australia only) or 61 2 6622 4933 (international enquiries) or email [email protected] if you have other queries and we will endeavour to assist.
Frequently asked questions
Q: What growing conditions best suit macadamias?
Although macadamia originated in subtropical rainforest it can tolerate a wide range of moisture conditions. Macadamia has the potential to adapt to poor soils with the aid of proteoid roots – intense clusters of short lateral roots which greatly improve the plant’s ability to absorb nutrients.
Soil should be 1-2m deep and well drained with a pH of 6.0 in 1:5 water (or 5.0 in CaCl~2~). Soils should be high in organic matter with an organic carbon content above 4%.
Macadamias will grow on a wide range of well-drained soils. Although macadamias will grow on steep hillsides and rocky sites, these should be avoided for commercial operations as they make cultural and harvesting operations difficult and costly.
Areas selected must be frost free, for even light frosts may damage young trees. Temperature is the dominant climatic factor influencing growth and productivity. Optimum growth and photosynthesis occurs in the narrow range of 20-25^o^C. Long periods of high temperatures can cause yellowing in new growth. This is seen in hot locations on the north west side of trees, when temperatures exceed 38^o^C after midday. In cooler months the symptoms disappear. Close planting and under tree irrigation can help reduce temperatures at hot locations like Rockhampton in Queensland.
Mature macadamias can with stand short periods of frost to 6^o^C, but young trees could be severely affected by frost of 1-2^o^C. Wrapping trunks to a height of 45cm can protect trees from light frosts.
Most growing areas in NSW range from 100-200m. During seasons with excessive cloud cover and frequent rain, reduced photosynthesis can increase shell thickness and decrease kernel recovery and Grade 1 kernels.
Water – rainfall, irrigation
Most genera of Proteaceae grow well in a climate where periods of wet and dry weather alternate. Research in NSW over 10 years showed that when annual rainfall ranged between 1,200-2,300mm, supplementary irrigation did not benefit producing trees. Increased irrigation rates decreased nut size and Grade 1 kernels but increased nut number without changing total yield.
Careful consideration needs to be given to the water requirements of macadamia in low rainfall areas – particularly if evaporation rates are high. Irrigation, with access to permanent water, is needed during protracted dry periods.
Macadamia is sensitive to saline water. Salt levels above 300ppm may cause scorching. Irrigation water should be tested, for salt levels can vary throughout the season and locality.
Macadamias do not have clearly defined tap roots and young trees are particularly sensitive to blowdowns in strong winds. Areas which do not experience strong winds are ideal, and exposed land should be protected by windbreaks.
Q: What is the preferred orchard layout for macadamias?
Plantations should be designed to allow for safe mechanical cultural operations. Avoid steep slopes to minimise the risk of soil erosion. Establishment of grassed waterways and shallow drains above and within the orchard, to carry torrential rainfall, should be discussed with the Soil Conservation Service before planting.
Orchard design should favour long rows to maximise land use and efficient machinery operation. North-south row orientation to allow sunlight on both sides of trees, particularly in winter, is favoured if all other considerations have been satisfied. Tree rows can be gently mounded, leaving a shallow broad based drain. Inaccurate levelling can cause erosion or ponding.
Tree variety, soil conditions and topography will affect planting distance which can vary from 6m by 3m to 10m by 4m. Staggered planting within rows to form equilateral triangles is favoured by some but in the main, trees usually form hedgerows after 5-7 years and diagonal thinning is rarely practiced.
Trees planted at high densities come into production earlier. The penalty for high density plantings, say 6m by 3m, is the higher initial cost of establishing an orchard. However, it reduces the time to reach a positive cash flow to offset the large investment required to establish macadamias.
It may be possible to delay tree thinning in a high density orchard by occasional trimming after harvest in winter. However, when production per hectare starts to decline, remove alternate rows to allow enough light to penetrate the canopy to maintain productivity. At this stage – 12 to 15 years – consider partially replacing existing varieties with new ones that are more precocious and produce higher quality nuts.
It is important to establish permanent windbreaks around exposed boundaries and along ridges. They should be established 1-3 years before planting the orchard. Australian native species such as casuarinas (Casuarina cunninghamiana) and tallowwood (Eucalyptus microcorys) can be used.
Deep ripping near the windbreaks reduces competition with macadamia trees. During plantation establishment use barner grass (Pennisetum purpureum spp) between every third or fourth row. Barner grass requires management to reduce competition with macadamia.
The grass should not impede air drainage in frosty areas. It should be cut every second year to stop it invading the orchard rows and becoming a rat haven. It is often removed after 5-6 years. When cut, baled and left for a month it provides excellent under tree mulch.
Q: How should I prepare my land for macadamias?
Tree stumps, large roots and surface rock should be removed but deep ripping is required only if there are hardpans or compaction layers.
Soil should be analysed and treated as necessary in the tree row after the grass has been killed with herbicide. Soil pH should be adjusted to 6.0 (1:5 water) or 5.0 (1:4 CaCl~2~) and lime or dolomite, phosphorus, copper and zinc added as required about three months before planting. A green manure crop can be used to protect the cultivated soil from sunlight and erosion.
Q: What do I need to know about planting macadamias?
Field planting of grafted trees in the autumn avoids extreme temperature. One or two hand waterings are usually enough to establish the young trees. Their roots have extended into the surrounding soil by the time temperatures increase in spring. If a spring planting is required a more comprehensive watering operation, or temporary irrigation system, will be required because of the likelihood of dry spells.
The young tree roots should be examined for any L-shaped, gooseneck or pot bound roots which must be pruned, otherwise the tree will not be able to withstand strong winds. A malformed root system will ultimately choke itself from an inadequate water and nutrient supply. Avoid advanced nursery trees with pot bound roots which will not move into the surrounding soil and establish a sound root system.
The planting hole should have rough sides and base so the roots can move out readily into the soil. About 50g of superphosphate can be mixed in soil at the bottom of the hole and 200g of dry pelleted, composted fowl manure added to the soil around the roots.
The tree can be positioned with a 100 lean in the direction of prevailing wind with the dominant bud facing in that direction. Use 10-20L of water to consolidate the soil around the roots. Avoid staking trees as self-supporting trees develop stronger trunks.
A ring 1m in diameter can be covered with a coarse fibrous mulch 5-10cm thick to reduce moisture loss, suppress weed growth and prevent excessively high soil temperature in the surface root area.
Direct contact of mulch with the trunk should be avoided to reduce the risk of trunk canker. After the tree has established, the lower leaves can be removed to avoid contact with any herbicide spray drift.
Trees planted in spring will require white plastic paint to prevent sunburn. Loose wrapping of trunks can protect against frost, animals, herbicides and sunburn.
Q: What should I look for when buying macadamia trees?
It is important to buy good quality planting stock when establishing an orchard. Avoid trees that are stunted, root bound or infested with pests or infected by disease. To ensure the orchard gets off to a good start, select vigorously growing trees free from nutrient disorders, insect pests and disease with a good healthy root system.
Buyers should look closely for:
A healthy well formed root system that is not spiralled or twisted.
A root system that has masses of very fine roots throughout the potting mix.
A potting mix that is well-drained, friable and free from water logging and hard compacted clods.
Healthy vigorous, well-formed growth with dark green foliage.
A minimum of 150mm of hardened new growth above the graft. This should consist of at least two growth flushes with a strong graft union.
Tress that are free from insect pests and diseases.
Q: When is the blossoming and cropping period?
Flower initiation occurs mainly during May with cool weather and shortened days. Prolonged overcast weather in early autumn can bring about earlier initiation.
The flower cluster is a raceme with 200 or more perfect flowers. Flowers are pink on M. tetraphylla and creamy white on M. integrifolia. Each flower has four stamens and a pistil with an ovary which contains two ovules. The flowers are protandrous – male first – with pollen being released 1-2 days before the stigma – female part – becomes receptive.
Most flowers first open from the basal or top end of the inflorescence and may take up to a week for the distal ones to open.
Heavy flowering may cause excessive carbohydrate depletion. After flowering only one ovule is fertilised and in many cases only about 1% of flowers set fruit. At about 5-8 weeks after flowering considerable nut drop occurs when nuts are about pea size.
Shell hardening takes place in early December followed by rapid oil accumulation in late December and January. Sunlight and warmth during the oil formation period may account for better quality. Dry periods during the oil formation period increase kernel recovery and Grade 1 kernels while wet overcast conditions depress quality.
Q: How long does it take a nut to develop?
Nut development in macadamia from full flowering (anthesis) to kernel maturity takes about 30 weeks. Anthesis in the last week of September would be followed by an exponential increase in growth at 4-7 weeks (October/November), and shell hardening in 14-15 weeks (end of December) at which time cell division is complete and no further growth takes place. For the next three months (January to March) nuts mature by converting sugars and starches to oil. This is a very important process which determines the final quality of the nut.
Q: How are macadamias harvested?
Preparation for conventional harvesting from the ground should begin in late summer with herbicides used to control grasses and weeds under the trees. Most nuts fall from the tree in late summer to early winter while still encased in the husk. The earliest falling nuts can be immature or insect damaged. It is desirable therefore to have an early harvest to remove any immature or last season's nuts. Damaged or poor quality nuts can be floated off in water tanks.
Machine harvesting is more economical than manual harvesting where total orchard production exceeds 35 tonnes. The action of mechanical harvesters can damage soil and roots. During wet conditions the use of harvesters is restricted.
There is no alternative to manual harvesting on steep slopes and rocky ground. A challenge exists to develop a harvesting technique which is cost effective and causes little damage to the soil surface. Harvesting remains the single most expensive operation for the grower and how it is handled can greatly affect nut quality.
Soon after harvest any excessively low limbs should be removed to facilitate the next harvest.
Q: What is dehusking?
Most nuts that fall are still enclosed in husks which have to be removed mechanically. Dehusk nuts within 24 hours of harvest otherwise considerable quality reduction can occur due to heat build up. If nut cannot be dehusked immediately it is best to leave them unharvested.
Macadamias fall from the tree with a moisture content of about 20%. It is usual to reduce this to 10% or less before selling to processors. Small lots of nuts can be air dried on shallow wire racks under cover on the farm. Large quantities are dried with unheated forced air in silos.
Further drying at the factory uses heat over several days to reduce moisture to about 1.5% ready for cracking. Growers are paid for percentage kernel recovery, quality and weight of nut-in-shell adjusted to 10% moisture. deductions are made for immature, mouldy, insect damaged or germinated kernel.
Nut-in-shell yield at 10% moisture is about 3-4 t/ha for wide spaced trees.
Q: How do I prepare home-grown macadamia nuts?
Follow these simple steps and you will have tasty macadamias ready to eat.
Let nuts fall naturally.
Rake from under trees, pick up and separate from leaves. Pick up at least once a week.
Remove husks. A large pair of pliers works well.
Spread the husked nuts in a shallow screen bottom tray in a dry place protected from the sun for 2-3 weeks.
Dry nuts further until shells are dry and brittle or nuts are loose in the shell and approach crispness. This can be done either by placing them in a mesh bag near a heater or wood burner (WARNING – do not let nuts get too hot as they can catch fire!) for 72 hours or more depending on nuts and amount of heat, OR, by placing them in a shallow pan in the oven at lowest temperature (about 50-60C).
Stir occasionally and watch that you don’t cook the nuts. The warm setting on an electric oven is about right. Time required is usually about 12 hours.
Store nuts in a cool place until needed – either store in a heavy plastic bag which prevents nuts from absorbing moisture, or crack and store nutmeats in a tightly covered container in the refrigerator or freezer.