Macadamia Nut Growers’ Guide – MacNut Farms

Macadamias require temperate to tropical climates that are frost-free.  Present experience suggests that plantings will be most successful in the Auckland and regions further North.Macadamias prefer soil rich in organic matter but can tolerate a wide range of conditions from clay to sandy loam.  Main requirements are good drainage, a pH balance of 5-6, plenty of light, protection from wind when young and average rainfall or irrigation if very dry.  Macadamias dislike frosts or sitting in pools of water but otherwise are very tough.Trace minerals such as magnesium sulphate, zinc, boron will help as will organic nitrogen.

Varieties

There are two main species of macadamia:

Macadamia tetraphylla comes from mid NSW and is more tolerant of cooler climates.  These trees tend to be vertical in growth and prickly with pink flowers and new growth.  Most rootstock is tetraphylla.

Macadamia integrifolia comes from Northern NSW and Queensland and prefers warmer climates, they are less prickly and rounder in shape.  The new growth is normally light green and flowers white.
Commercial varieties are inevitably hybrids, which show several of the characteristics of the above species.  In general NZ grows hybrids with tetraphylla characteristics.

Commercial macadamia trees are generally grafted from a good rootstock variety.

The main grafted varieties that have been planted in NZ are shown below.  These varieties have now been largely replaced by new and improved hybrids.  Advice should be sought from www.macnz.com for the latest types suitable for NZ’s cooler climate.

Beaumont
A good quality nut that does best on warm sites but is difficult to pollinate.  Must be handpicked and may have too much vegetative growth on cooler or fertile sites.

PA39
Matures early and tends to drop nuts, a tetraphylla like hybrid that crops well and combines well with Beaumont as a pollinator.  Easily infected with veggie bug.  May need pruning to remove denseness.

GT1
A good self or cross pollinator which can crop heavily with smaller nuts and may require extra feeding.  The tree is less dense and prone to wind damage.

Renown
An open tree with good crop and is a good pollinator.  A good variety for home use with large and at times irregular nuts.

Own Choice
Another good variety for the domestic garden with good self or cross pollination, large nuts and few prickles (Integrifolia characteristics).  Tends to crop inconsistently and year round which is not much use commercially!

Elimbah
Attractive tree with inconsistent crops and many pink flowers in season.

There are many more varieties about which specific advice can be sought from a nursery.

As ground collection is generally unsuitable for NZ’s wet condition trees with good cropping characteristics and suitable for hand picking are preferred in NZ.

No planting of a single variety is recommended as macadamias do better when the various types are mixed to allow cross-pollination, thus increasing yields.

Planting

Macadamias are best planted in spring.

Trees should be planted in rows with a 6m row spacing and minimum 4m spacing between trees allowing for ingress of light, air and insects for pollination and room to grow to maturity.

Young trees can be protected by shelter belts, which can be removed later.  Mature trees still require some protection due to their brittle nature but large shelter belts will effect light levels and a balance must be sought.

If dry months are predicted an irrigation system may be useful. Ensure the water is of hygienic quality.

Pruning

Some pruning is desirable after planting to reduce the tree to two leaders at each branching.

The tree should be manicured to allow for light, picking and air movement in the center.  The tree can be thinned to a minimum of internal branches without effecting production.  Height should be limited to picking height.  After pruning new growth may also need to be trimmed.

Weed & Pest Control

The main problem for NZ macadamias is the green vegetable bug, which can pierce the immature nut and stain the kernel brown, making it unsaleable.  We spray with Deltaphor 25 EC three times a season at intervals of three weeks, and 3 weeks after flowering (so pollination by bees is not affected).

After this period the nut should be hard enough to resist attack.  Towards the end of flowering (September) one preventative spray with Dipal for the Leaf Roller Caterpillar is advised.  Alternate measures for pest control include chickens or possibly wasps that will out-compete the veggie bug.

Where chemical control measures are undertaken ensure these measures are in compliance with health and safety regulations for application and the possibility of the retention of toxic residues.

Rats can be a problem and an eradication program is advised.  The rats often reside in bird’s nests or piles of rubbish or weeds and these should be removed.

Possums will eat soft greens nuts and goats the whole tree in early years (although goats prefer other trees to macadamias).

Trees should be kept clear of weeds using either a herbicide like ‘Roundup’, mowing or sheep.  (We use sheep, which do not disturb mature trees but are not good for ground harvesting)

Accurate records of pest and weed control measures will allow optimisation in future years.

Fertiliser

Annual leaf and soil analysis should show up deficiencies and point towards a fertiliser program.

Applications of trace elements can be achieved in airborne sprays.

In addition ground based applications of superphosphate or organic manure or mulch can provide valuable nutrients.  In particular a good source of mulch will be the prunings and husks from the nuts.

Avoid heavy application of nitrogen in summer as this can promote vegetative growth at the expense of nut quality and quantity.
Accurate records will help determine the effectiveness of any program.

Yields

Top orchards in NZ have returned yields of 4-6 tonnes per hectare.

To estimate the crop sizes for a well-tended orchard use the following as a guide:

Nuts should be husked within 24 hours of picking to prevent respiratory heat in storage, which can in turn increase mould, rancidity and germination.  If the nut cannot be husked immediately the nut in husk should be well ventilated and dry.
Rocks and debris of a large nature should be removed from nuts before husking.  Husking machinery should be checked to ensure that the nuts are not being cracked or bruised in the process.

NIS (Nut in Shell) Drying & Storage

Moisture after dehusking is normally around 25% and must be reduced to around 1.5% for cracking.  Nuts should be crisp when fully dry and will rattle when shaken to indicate that the kernel has shrunk away from the shell.

Nuts should be hung in a well-ventilated place to reduce moisture content before transport to the processor.  The minimum moisture content that can be achieved without commercial drying is around 10%.  Failure to store in a dry well ventilated pace will lead to mould, rancidity and germination.

Contamination or wetting of nuts in storage should be of highest concern with special attention paid to ensure that no condensation in the storage area or leakage from outside can occur.

Avoid prolonged exposure to direct sunlight, which can increase rancidity and cracking of the shell.

If using heating in the drying process do not use temperatures in excess of 38 deg C if the NIS moisture content is above 10% as this can create browning of the kernel.

Do not store nuts for prolonged periods at moisture contents greater than 10%.

Transport To Processor

Take precautions to ensure chemicals, foreign debris or manure during transport does not contaminate the nuts.  Cover the macadamias during transport to ensure the nuts arrive dry and clean.

Avoid drop heights greater than 2m as nuts may be cracked or bruised in handling.

Delivery to processing should be immediate after removal from well-ventilated dry storage.  Transport times greater than 24 hours can result in increases in rancidity and mould.

Ensure adequate information about type, time of picking and storage conditions is provided to the processor to allow optimum processing.  Label any nuts to identify ownership and date of transport.