Macadamia

Macadamia nuts

Macadamia integrifolia

Macadamia integrifolia Trunk
Trunk

Genus: Macadamia.

Species: integrifolia. Other species (jansenii, ternifolia, tetraphylla).

Family: PROTEACEAE

Common Name: Macadamia. More traditional Aboriginal names: bauple, gyndl, jindilli and boombera.

Etymology: Macadamia: Named after Dr John Macadam (1827–65) by Ferninand Mueller (Director of Royal Botanic Gardens, Melbourne) honouring his friend. Interestingly John Macadam was also involved in organising the Burke and Wills expedition. integrifolia: entire, undivided (leaves).

History: The Macadamia is an Australian native rainforest tree growing naturally from north-eastern to south-eastern Queensland on the slopes of the Great Dividing Range. Macadamia integrifolia and Macadamia tetraphylla are the only trees where the nuts can be eaten raw. They were known to the Aboriginal people for thousand of years and were considered a delicacy, cracked and eaten raw or roasted on the fire. They were also traded between tribes and used as special ceremonial gifts at inter-tribal corroborees. Isolation kept the Macadamia secret from the rest of the world until they got the attention of  Walter Hill (European botanists and director of Royal Botanical Gardens Brisbane at the time) and Ferdinand Von Meuller (refer blog post 1st Feb 2016) in 1858. Although discovery is attributed to Allan Cunningham in 1828, it wasn’t until 1843 that German explorer Ludwig Leichhardt took a sample to Melbourne (now in National Herbarium Melbourne) that it was named and classified. Apparently Walter Hill asked one of his young associates to crack some of the nuts for germinating, the associate decided to eat some claiming them delicious. Hill (a little more cautious and ensuring his associate didn’t die from poisoning) waited a few days before trying them himself and after trying the tasty nut cultivated the first Macadamia integrifolia in the Brisbane Botanical Gardens, a tree that is still alive and bearing fruit to this day. The first commercially grown Macadamia trees were planted by Rous Mill in the 1880’s about 12km south of Lismore, NSW but this was more of a boutique industry. Seedlings were also sent to Hawaii during this decade as windbreaks for sugarcane (that failed because Macadamia’s also need shelter from wind but this lead to the beginning of the industry there). The first extensively commercial industry was established in 1922 by Van Tassel and called the ‘Hawaaiian Macadamia Nut Co’. Research from Hawaii is what the whole industry is based on today. In Australia it wasn’t until 1932 that Greek fruiterer Steve Angus and Tweed farmer John Waldron got together (in Murwillumbah) that the industry started to grow in Australia. Angus purchased a nut cracker from the USA and started a company called ‘Macadamia Nuts Pty. Ltd’ sourcing most of his nuts from backyard trees in the beginning. The Angus family opened Australia’s first purpose-built processing plant at Slacks Creek in 1964 and Macadamia production surpassed Hawaii in 1997. Australia is now one of the largest producers of Macadamias in the world with nuts being also sold commercially in (obviously) Hawaii, South Africa, Brazil, California, Costa Rica, Israel, Kenya, Bolivia, New Zealand, Columbia, Guatemala, Malawi and it is tipped that China will be a big player in the future as their trees mature.

10 Uses for Macadamias: The macadamia nut is a high energy food that has no cholesterol.  It has virtually no Omega 6 (which can be pro inflammatory in large amounts). The average nut is made up of  76% natural oils, 9% protein, 9% carbohydrate and 2% dietary fibre. The remainder contains the vitamins thiamine (Vitamin B1), riboflavin and niacin as well as other essential elements like calcium, phosphorus, potassium, sodium, selenium and iron. It promotes weight loss and helps with a healthy heart.

  • Burnt shells make excellent carbon and charcoal filters for water and air purification.
  • Cooking fuel on BBQ or spit roast as charcoal (slow burning and no unpleasant taste from smoke).
  • Cooking oil.
  • Fertilizer (shells hold nutrients and make a good fertilizer).
  • Ingredient in many recipes or as a tasty snack on its own (works equally well in both sweet and savory applications).
  • Lowering total and LDL cholesterol levels.
  • Mulch (shells in the garden)
  • Oil has a number of applications for healthy skin, hair and nails.
  • Powerful antioxidant.
  • The tree of coarse makes a beautiful addition to your garden.

Basic description: Small to large rainforest tree 5-12m high, 4-6m wide. The leaves are arranged in whorls of three to six and are lanceolate to obovate or elliptical in shape (6-30cm long and 2-13cm wide). It bears long slender trusses of cream flowers (5-30cm long), followed by very hard, woody edible nuts.

Macadamia requirements & maintenance: pH 5.5-6.5 (very acid to acid) Best suited in a warm temperate to sub-tropical climate that is frost free and away from strong winds (optimum growth between 20-25 degrees Celsius). Macadamias prefer a moist, fertile soil with good drainage. They do grow rather large but can be trimmed to keep them at a more desirable height. They do require good rains or irrigation for successful crops. When young it is important to keep the tree sheltered from the harsh sun and being shallow rooted it is important to mulch which will protect roots and stop competing weeds from growing near trunk. As with many native trees, the Macadamia is phosphorus sensitive so use a native fertilizer.

Harvesting time: Macadamias can take between 10-15 years before maximum yield, however, should start producing nuts between 4-6 years. Flowers occur in early spring, followed by nuts in early summer. Shells begin to harden in December with rapid oil accumulation over the coming 2 months. Mature nuts fall to the ground between March and September ready for harvesting. De-husk immediately and dry for three weeks before cracking nut (this allows the kernel to separate from the shell).

Companion plants: Not applicable as Macadamia does not like root competition.  

Problem Solving without chemicals:

  • Anthracnose: Fungus that lives in dead twigs, leaves and fruit and spread through the warmer months by splashing water. It causes small, light brown, circular spots that quickly get bigger until the whole husk is rotted but shell and kernel are not effected . It becomes active when fruit is damaged or when it ripens. Prune out dead twigs and remove effected fruit from the tree. Leaf spot does not generally require treatment.
  • Banana spotting bug: Bug elongated in shape about 15mm long (very similar to fruit-spotting bug but a slightly lighter green). Sap sucking causes water-soaked area from which sap exudes and drys white later with narrow cracks around them. Avoid planting trees close to native bushland. Assassin bugs and spiders prey on bug.
  • Blossom blight: Fungus that is active in wet weather between 10-20 degrees Celsius. It attacks decaying petals but can spread to flowers on the rest of raceme destroying part or all of raceme. This disease is totally weather related and little action is required except to avoid overcrowding of trees allowing better airflow.
  • Fruit-spotting bug: Australian native green-brown bug about 15mm long with prominent antennae that when disturbed will fly away or somersault to lower branches or quickly hide behind fruit and under leaves. Eggs are 1.7mm long, pale green and somewhat triangular. Both adults and nymphs feed by piercing shell and sucking the juice from the tissue. They insert their long mouthparts into the fruit and in feeding, exude saliva containing enzymes that break down the cells damaging the kernel that is unnoticeable until shell is cracked open. Avoid planting trees close to native bushland. Assassin bugs and spiders prey on bug.
  • Green vegetable bug: Adult up to 15mm long (usually green but emerging brownish after winter hibernation) with black spot in middle of back and 3 small yellow spots. Adults and nymphs (marked yellow, red orange green and black) are both sap sucking but older bugs prefer fruit and seeds. Hand pick and control weeds. Nymphs are attacked by ants, spiders and preditory bugs.
  • Husk spot: Fungal disease causing large yellow to brown spots on nut that cause premature nut drop. Nuts that wont drop (sticktights) should be removed as they are a good source of incubation for the disease. Keep area below tree free from diseased husks.
  • Iron Deficiency: Yellowing of new leaves, can even go from yellow to white in extreme cases. Low winter soil temperature, poor drainage and high pH.
  • Latania scale: Small (2mm across) pale grey with light brown centre insects that have hard shell and attach themselves (usually) to underside of leaves (in veins) and along branches and nuts. Use White-oil at recommended dose on bottle, control ants that also help spread them.
  • Macadamia felted coccid: Australian native insect, 1mm long and white to yellow brown. They gather on leaf axils,in bark crevices, between buds and along veins under leaves causing distortion and stunting of young growth, even death in young trees. Introduce ladybirds and preditory wasps, spray with white oil.
  • Macadamia flower caterpillar: 12mm long and vary in colour from light green to grey to reddish brown with some longitudinal strips feeding inside then outside of buds and flowers. Observation and hand removal is best as there are many predatory bugs and wasps that should keep this caterpillar in check.
  • Macadamia leafminer: Thin blister-like lines under leaf surface. Remove leaf when spotted. Spray new growth with white oil as a preventative (only really effects young trees as older trees will tolerate damage with little effect). Do not prune tree as this will encourage new growth and more pests.
  • Macadamia nut borer: Larvae of Moth that are active Dec-Feb attacking immature nuts before they harden causing nutfall. Nuts may have sawdust and webbing on the surface. Squash eggs (white 1mm long) on immature nuts.
  • Macadamia twig-girdler: Moth larvae up to 23mm long, dark brown heads and paler mottled bodies with rows of black dots. Found mostly on young trees where they can stop tree growth or even kill it by defoliating it, they even bore into nuts. Sheltering in tunnels of webbing that often have sawdust stuck to them. Not necessary in mature trees. Observation and hand removal, there are more than 20 native insects, mostly wasps that attack this larvae keeping numbers down.
  •  Nitrogen deficiency: Yellowing of leaves beginning in older leaves, can happen towards end of winter or early spring when plants nitrogen levels are low and soil is cool. Add nitrogen rich fertilizer to correct problem.
  • Phytophthera root rot: Pathogen in wet soils that rots roots causing yellowing and dieback of plant from the tips. It is spread in water through chemical stimulus as well as root-generated electric fields. Add compost to soil (stimulates competition also ammonia and volatile organic acids released by decomposing organic matter kill Phytophthora), improve drainage.
  • Rats: Keep area free from fallen nuts and clean and tidy of rat friendly habitats such as Lantana where Rats can hide and build nests. Remove any nests located immediately. Encourage birds of prey such as owls by building perches.

Growing macadamias: Macadamias can be grown from seed but tend usually to be propagated from cuttings and grafting as this produces the best result. They can be grown in pots and Macadamia tetraphylla will even will grow as far south as Tasmania (obviously taking a lot longer to be productive though). They can grow rather tall but there are many dwarf varieties for limited spaces.

Macadamia integrifolia Seedling
Seedling

References:

  • http://theseedsite.co.uk.
  • What Garden Pest and Disease is That by Judy McMaugh.
  • Wikipedia.
  • www.australian-macadamias.org.
  • www.daf.qld.gov.au.
  • www.ehow.com.
  • www.gardeningwithangus.com.au.
  • www.macadamiacastle.com.au.
  • www.mpcgrowers.com.au.
About Simon 93 Articles

Simon Schubert is a qualified Horticulturist who enjoys gardening and bush-walking. He has a keen interest in science, the natural world and particularly our environment. He would like to share his experiences and knowledge while learning better practices that will hopefully benefit the future for us all. Please join him on some fun adventures while learning about the life of plants and other interesting facts about our world.

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