In these unsettled times, with the threat of food shortages looming, it’s always good to take stock of what sorts of things can be grown or produced locally. With many of us adopting diets where the plant-based components are increased, things like grains, legumes and the traditionally-expensive nuts come under the spotlight. Previously I’ve mentioned walnuts and almonds as potential candidates for backyard cultivation in New Zealand, but if you have enough room to swing a tree-planting spade, consider planting a few macadamias.


My Dad has always been fond of macadamias and on one occasion I found a bin of unshelled nuts at the local produce market and took a bagful with me on a trip home to visit. Well, he tried every known method of getting through those tough, glossy brown shells and failed every time. The most entertaining was when he tried the vice in the garage, but those slippery, shiny spheres still got the better of him and went ricocheting off in every which direction. As a result, the bag of nuts adorned his desk for a year or two before eventually finding their way on to the fire (I think). Thankfully, there are now small and large scale macadamia-specific nutcrackers readily available, so extraction of these luxurious kernels is now within the grasp of the common people. Touted to be one of the tastiest edible nuts, with an impressive 60-80% oil content, the long-lived evergreen trees also make fantastic ornamental specimens. With the right climate and a little effort, time and patience you could become the envy of your friends as you harvest bucket after bucket of these highly sought-after nutty delights.


Macadamias: a short family history
As a university student I was once tasked with making a collection of various botanical specimens as part of an assignment. One such specimen was required to be “from a plant with proteaceous roots” and I sought out, predictably, a nondescript flowering Protea of some sort growing in a bed outside one of the campus buildings. It wasn’t until a few years later that I found out that the good old macadamia is indeed also a member of the Proteaceae, alongside ornamental stalwarts the banksias, waratahs and grevilleas and our own endemic rewarewa (Knightia excelsa). The family is an ancient one, dating back to the time of Gondwanaland. Native to the warm-temperate, tropical and subtropical regions of Australia, the macadamia is also known in Australian Aboriginal dialects as bauple, gyndl, jindilli or boombera, depending on location. It is also known as the Queensland or Australian nut, bush nut, maroochi nut or Hawaiian nut (more about the latter, later). Several of these common names are self-explanatory but I hear you asking, what’s in the name macadamia? It turns out that the genus Macadamia was named after one Honourable Dr John Macadam, a Scottish-Australian chemist, man of medicine and notary public. His friend and colleague, Director of Melbourne’s Royal Botanic Gardens Ferdinand von Mueller described the genus in 1857 and named it in honour of his friend. Nice.


There are four species in the genus: Macadamia jansenii (endangered), M. ternifolia, M. integrifolia and M. tetraphylla. Nuts of the two former species contain cyanogenic glycosides (which we met in Your Backyard Fruit Bowl: Almonds) and are poisonous, as are the nuts of a relative easily mistaken for true macadamias, Lasjia whelanii (Whelan’s silky oak or Whelan’s macadamia). The latter two species produce edible nuts, hybridise readily in nature and have given rise to all the modern commercial cultivars. Macadamia nuts were introduced to Hawaii in 1882 for use as a windbreak species for sugarcane plantations, with expansion as an actual crop to supplement coffee production in 1910 and rapid growth of the industry in the 1930s saw Hawaii become the leading producer of macadamia nuts. A smaller area was also under cultivation on the US mainland in California. Native Australia surpassed Hawaii/the USA to become the major producer in 1997. Macadamias have reportedly been present in New Zealand since 1875 and the first orchard was planted by a Mr Jolly, who planted nuts for a seedling orchard in Kerikeri in 1932. They were planted in South Africa prior to 1915 and around 2015, South Africa pipped Australia to become the number one macadamia producer worldwide. The New Zealand macadamia industry produced 60,000 kg of useable nuts in 2018 but imported 185,000 kg, so there is considerable demand for the produce and therefore scope for expansion of the local industry. For some macadamia trivia, the ‘King of Nuts’ was implicated in the infamous Korean Airlines ‘nutgate’ incident of 2014 – read more here: https://en.wikipedia.org/wiki/Nut_rage_incident Funnily enough, sales of macadamias in Korea skyrocketed as a result.


Suitable climates and growing conditions
In their natural Australian habitat, you will find macadamias growing in rainforest areas, with a predilection for stream banks. They thrive in warm temperate, sub-tropical to tropical climates, so in New Zealand, are most suited to the northern areas of the North Island, the Bay of Plenty and Taranaki but they actually do very well in coastal Nelson/Tasman and Marlborough in the South Island too. The general New Zealand rule of thumb is, if you are in an area where you can grow tamarillos, you can grow macadamias too. An average summer temperature of around 25°C is ideal. They do not have a winter chill requirement and whilst young trees (<3 years of age) are frost-tender, older mature trees will withstand frosts down to about -3°C and as low as -7°C for short periods in their dormant phase. M. tetraphylla cultivars are more cold tolerant, requiring a distinct seasonal change in temperature and diurnal variation to produce well. You can swaddle the trunks of young trees from May to September with insulating material such as fibreglass batts, jute sacking or even newspaper, giving the canopy time to develop and protect the trunk. Conversely, macadamia bark is susceptible to sunburn, so it is advisable to paint the trunks with white water-based paint in summer. High summer temperatures (>30°C) can also reduce yields, so it is worth noting that M. integrifolia cultivars are the ones better suited to warm climates.


Macadamias aren’t so well suited to small gardens, as you do need to plant a few and they fall into the medium to tall height category – about 12 m high for M. tetraphylla, up to 20 m for
M. intergrifolia and upwards of 8 m in width. Pruning is recommended to keep orchard management easy. The trees are relatively slow-growing, but grow steadily in the establishment phase (first 4-5 years of age) and are long-lived. Most cultivars will start producing a crop at around 3-5 years of age for grafted trees and around 10 years for seedlings. You can expect a mature tree to produce about 10-20 kg of in-shell nuts a year, of which 30-40% of the weight is edible kernel and the rest husk and shell. Don’t despair, as the hulls make excellent mulch and the shells great fuel for your logburner. Nut production will help slow vegetative growth, of which there are two flushes each year, in spring and then again in mid-summer.


Macadamias flower in winter, with some variation between flowering time by cultivar and as a result you can have flowers, immature nuts and nuts ready to harvest on the same tree at the same time. Pollination is by insects (such as honeybees and interestingly, the moths of leafroller caterpillars, a common crop pest), most likely supplemented by some wind pollination. Macadamia flowers are perfect (bisexual) and cultivars range from self-fertile to self-incompatible, so it is always best to have polliniser varieties amongst a block of trees. Flowers are borne in long showy clusters (racemes), 15-30 cm for M. integrifolia and up to almost 40 cm for M. tetraphylla, with only one or two percent of flowers going on to set fruit. It takes approximately 7-8 months after fruit set for nuts to be fully mature. The flowers are highly fragrant and a bee magnet.


You may have to seek out a specialist nursery to source your desired macadamia cultivars, being less commonly available than other nut trees. As with most other tree crops, seedling macadamias take longer to bear than their grafted counterparts, but fresh nuts germinate readily and can make a good try-at-home project. With patience, you can grow them on as trees, or have a go at grafting yourself once the seedlings are 2-3 years old if you have access to suitable scionwood. Select fresh nuts that have not been allowed to dry out and carefully remove the hull – if you damage the shell in the process, this may inhibit germination and/or encourage fungal infection. Float test the nuts in water and choose the ones that sink for planting. Sow at a depth of approximately 3 cm in pots containing standard potting mix, with the white spot on the nuts facing downwards. The nuts should germinate in 2-4 weeks, with fibrous roots forming first, followed by the tap root. Keep the pots in a sheltered position, with warmth but out of direct sunlight. M. tetraphylla seedlings are generally more vigorous than M. integrifolia.


Site selection and planting
The best time to plant macadamia trees is in spring or autumn. Being fairly large trees, it is advisable plant at a 6 x 6 m spacing. Choose a site that is sheltered, as macadamias have hard but brittle wood and the branches may snap in high winds. A gentle north-facing slope is ideal, catching the warmth of the day and allowing cold air to drain away. Shelter will also provide some summer shade if you live in a warmer climate. Their salt tolerance (soil or airborne) is low, so macadamias are not a good choice if you live on a windswept coast.


A unique feature of the Proteaceae is that the plants in this family have structures known as proteoid roots – proliferations of short lateral roots which arise from the taproot. Proteoid roots provide an increased surface area for the plant to absorb water and nutrients through, enhancing overall growth. Macadamias prefer deep, free-draining soils of average fertility – high fertility soils actually discourage proteoid root development. Sandy and volcanic soil types are ideal, although heavier types such as clay are also tolerated.


Culture and care
Being a rainforest species, macadamias appreciate good moisture levels all year round. Those of you in higher rainfall areas but with good drainage may be in luck. The trees can tolerate some drought stress due to having a deep taproot, but cannot cope with waterlogging, which leaves them highly susceptible to root rots such as Phytophthera. Adequate irrigation is particularly important when the trees are young, at flowering and fruit set and during the second vegetative flush in mid-late summer.


Although they are not gross feeders, macadamias benefit from 3-4 applications of a general fertiliser with trace elements. Larger orchards base fertiliser requirements on the results of soil and leaf tests, but for the home orchardist, citrus fertiliser works well. Start with 0.25-0.5 kg per year of tree age, building up to a maximum of 5 kg/tree at maturity (10 years of age), splitting the total amount into at least three separate applications throughout the year. Apply prior to rainfall or water in well with a hose. Too much fertiliser encourages excess vegetative growth – you won’t get many nuts and the tree’s growth will be thrown out of balance as a result.


Pruning
Things to keep in mind when pruning your macadamias are: providing the framework for a good structure, allowing light to reach the lower branches; pruning the tree so you have easy access at harvest and managing the overall height of the tree – ideally no more than 3-4 metres. Some macadamia cultivars drop their nuts at maturity, others hold on to them - pruning is slightly different for each type. Some growers in cooler climates find all the nuts tend to stay on the tree. As a rule of thumb, aim to remove strong upright leaders from ‘stickers’ and prune around the outside of ‘droppers’. If you have two overlapping branches, remove the upper one, and as with general pruning, remove any crossing over each other and any dead or damaged branches close to the trunk. To keep tree height in check, any weakly forked branches can have a leader removed completely, or shorten the length of both or all if there two or more. Thin, whip-like leaders which are taking off can be pruned back to 0.5 m above the last branch. Plan to prune your trees soon after the harvest is complete.


Pests, diseases and what to do about them
The southern green stink bug, Nezara viridula, more commonly known as the green vegetable bug is public enemy number one of the macadamia grower (and just about every gardener I know – even my chickens only eat every second one I proffer, and that’s on a good day). These smelly ne’er-do- wells pierce the nut with their needle-like mouthparts, causing staining and spotting of the kernel. If you’re not keen to spray, make sure you keep the grass around your trees mown or grazed short and let your chickens loose. There is a self-introduced parasitoid wasp, Aridelus rufotestaceus, which parasitizes green vegetable bug juvenile instars and adults.


The polyphagous guava moth, Coscinoptycha improbana (also an Australian native) is another significant macadamia pest, with its alternative common name, the fruit driller moth, giving an indication of the ease with which can bore into ripening nuts. First detected in Kaitaia in 1997, its presence is now felt throughout Auckland and the Waikato - as far as we know it has not yet made it to the South Island. The insect spends much of its lifecycle inside fruit, with the larvae burrowing in a day after hatching from eggs, which makes spraying for control a difficult endeavour. Those who do spray commence three weeks after flowering, then re-applying at three week intervals for a total of three applications per season. Those who do not can suffer crop losses of up to 30% in a bad year. Remember to keep in mind a heavy-handed approach to insecticide sprays may have a deleterious effect on the light brown apple moth and other leafroller adults who contribute greatly to macadamia pollination – a literal beneficial pest, that’s one for the strange but true files.


Rats are also great fans of macadamias, so keeping your orchard free of long grass is the first step towards controlling their impact, as is regular trapping or baiting. They will start chomping on the nuts in summer, a good five months before harvest, so be vigilant.


Varieties: My top picks
There are some distinct botanical differences between the two main edible macadamia species. Timing of harvest will vary depending on where you are in the country, July through to September-October covers most regions.


M. tetraphylla species

  • Four leaves present at each node
  • Leaf margins serrated, with many spines along the margins
  • Nut shells coarse, fibrous and brittle
  • Kernels have a tendency to shrink after harvest
  • Oil content is lower than M. integrifolia
  • Sugar content is higher than M. integrifolia
  • Have pink-reddish brown flowers


M. integrifolia species

  • Three leaves present at each node
  • Edges of leaves have fewer spines than M. tetraphylla species
  • Round nuts with thick, smooth shells
  • Kernels are uniform, white and tender to the bite
  • Less nut shrinkage after harvest
  • Higher oil content than M. tetraphylla
  • Lower sugar content than M. tetraphylla
  • Can flower and crop throughout the year
  • Have creamy-yellow flowers

Renown

Some say M. tetraphylla, some say hybrid. Recommended for home orchards. Large, elliptical nuts but not suited to mechanical cracking. Nuts are ‘droppers’.

Beaumont

A well-known hybrid from Australia with an upright growth habit. Good-sized ‘sticker’ nuts with a moderately hard shell. Nelmac 2 is a suitable polliniser.

GT201

A New Zealand-bred cultivar from the Gordon Titirangi series. A consistently heavy cropper, average sized nuts which are easy to crack. Improved tree shape compared with the earlier GT cultivars.

Nelmac (sometimes Nelmark)                                                                                                                   

South African hybrids.

Nelmac 1 – A light-cropping ‘dropper’ with thick-shelled nuts. Flowers late and produces high quality kernels with a high oil content.

Nelmac 2 - Produces large nuts with a high crackout percentage. Crops well in the North Island and is a polliniser for Beaumont.

Own Choice

A hardy, self-fertile cultivar, so a good choice for smaller properties as you may get a crop with just one tree. Nuts are ‘stickers’. Somewhat susceptible to Botrytis. Proven to do well in New Zealand. A suitable polliniser for Beaumont.

What to do with your crop

Macadamias require some specialist postharvest handling to ensure a perfect end product. Depending on whether you have droppers or stickers, you will either be collecting nuts from the ground (regular pick-ups are essential) or hand-harvesting from the trees – choose a dry day. You may find it easiest to cut off the entire bunches of nuts (just like picking grapes) if they stay on the tree. Make sure you mow under the trees prior to harvest or you could spread a tarpaulin on the ground to catch any strays. M. integrifolia cultivars will hold their husks tightly around the mature fruit, whereas M. tetraphylla husks split open.

Either way, make sure you remove the husks preferably within 24 (maximum 48) hours of harvest. Store the fresh, hulled nuts in onion sacks or perforated crates in a cool, well ventilated rodent-free location for at least three months. You are aiming for about 15% moisture loss weight wise. After this period, pop the nuts somewhere warm and dry for a few more weeks (the hot water cylinder cupboard is recommended for domestic quantities), where you can expect a further 10% moisture loss. If you can hear the kernels rattling inside the shells, separation has been achieved and your drying mission is complete – on to cracking and shelling. Store shelled nuts in plastic ziplock bags in the freezer, removing them for roasting as necessary – I let mine come to room temperature before they go in the oven. Macadamias can be eaten raw, but reach peak perfection when very lightly roasted (at 125-150°C for about ten minutes, until a golden colour and toasty aroma is just creeping in – watch carefully!).

I am very lucky to have access to a local source of macadamias and often use them in place of imported cashews. They are relatively low in protein compared to other nuts, but contain flavonoids, vitamin E and are also a good source of B vitamins. I don’t think you’ll find a more versatile nut – they are equally at home in baked goods as they are in savoury dishes. They produce a light, straw coloured oil which is highly sought after for cosmetics and I’ve also heard it makes wicked roast potatoes. The flavour is delicate but distinctive – I recently blended some up as a cashew replacement in a creamy, spicy, dairy-free soup and although the texture was definitely chunkier, they added the necessary body to the dish.

Macadamias shine in brownies and chocolate-chunk cookies and make a great addition or crunchy topping for ice cream. They are the ultimate snack raw, lightly roasted, caramelised with a coating of honey, with a hit of chilli or best of all, covered in dark chocolate. Throw some on your next cheeseboard, in your next batch of pesto or try the following recipe for simple but tasty macadamia burger patties.

Please take heed – macadamias are acutely toxic to dogs, so keep them out of reach of your canine companions.

Macadamia Burgers

For 4-6 patties

1 - 1 ½ cups shelled macadamias, coarsely chopped
A medium onion, peeled and diced
1 cup fresh breadcrumbs
Vegetable oil, for frying and a tablespoon for the patty mix
1 egg
½ cup chopped red capsicum (bottled is fine) or sundried tomatoes
1 medium carrot, peeled and grated


Chilli or any other preferred herbs and spices
Salt and pepper, to taste.


Sauté the onion in frying pan with a little oil until softened. Combine with all the other ingredients in a large mixing bowl, then shape scoops weighing about 85-90 g into thick patties. Dunk your hands in warm water first to make the job easy. To check the seasoning is to your taste before you cook the whole batch (always hard with ‘raw’ mixtures like this), you can make a mini-patty first to cook separately, then adjust the seasoning to your liking before you fry the rest.


Cook until well-browned on a BBQ or grill, approximately five minutes per side – a layer of non-stick aluminium foil may help keep things together. Serve immediately with salad, bread rolls and some pickle or chutney.


Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/

Image credits
All photos - Ann & Bob Phillips