If you are looking to add an attractive evergreen tree to your garden, look no further than the macadamia nut tree. This majestic glossy broadleaf specimen, the foliage of which is similar to that of the holly bush, is an increasingly popular garden design choice.
A versatile choice, these specimens can be used in a number of different ways. A macadamia nut tree, for example, is a good way to introduce shade to an open, sunny spot. Adding further interest are the spring flowers, which range in color from pink to white, and edible fruits.
If you want to learn how to grow a macadamia nut tree, this guide is filled with all the information that you need.
Warning, the macadamia nut has a high level of toxicity that can make dogs ill if consumed.
The macadamia nut tree is an attractive addition to any landscape. Macadamia trees by Jenny Brown / CC 2.0
What is a Macadamia Nut Tree
The macadamia nut tree is a broadleaf evergreen which produces attractive springtime flowers and fruits. These ripen at random points during the growing season.
Of the 4 recognized main types of macadamia nut tree, 2 produce edible fruits.
The macadamia genus was first recorded in the Australian rainforests in the 1800s. Eventually, the plants were transported to Hawaii where cultivation for commercial purposes began. Over time the genus grew considerably in size. It was often grouped under the M. Integrifolia name. However, re-classification has led to the size of the genus shrinking.
Today, there are 4 species in the Macadamia genus. These are:
- M. Integrifolia, a commercially grown crop that produces a sweet nut with a smooth shell. Also known as the Queensland nut. It produces attractive light green shoots and large, 11 inch leaves that are arranged in groups of 3.
- M. Jansenni, an endangered species that produces bitter fruits. Also known as the Bulberin nut.
- M. Ternifolia or the Gympi nut. This is another endangered species that produces bitter fruit.
- M. Tetraphylla is a commercially grown plant that typically produces a sweet nut with a rough shell.This cultivar produces pink shoots and large 20 inch leaves that develop in groups of 4.
Of the 4, M. Tetraphylla has the greatest heat and frost tolerance. Unlike M. Integrifolia its fruits contain variable amounts of fat and sugar. These produce variations in color and texture when roasted.
- Tetraphylla and M. Integrifolia are both commonly sold in garden stores and plant nurseries. Many plant nurseries also sell hybrids, these are a cross between the two common varieties.
Some varieties produce edible fruit. Macadamia-Nuts by Peta Hopkins / CC 2.0
Different Macadamia Nut Varieties
A popular garden design choice, you can find specimens for sale in larger garden stores. Specialist plant nurseries stock a wider range of varieties.
Some of the most attractive cultivars that are widely available are:
- Beaumont, an Australian hybrid cross between M. Tetraphylla and M. Integrifolia. Beaumont displays an upright growth habit. It produces showy pink flowers and medium to large fruits. This is a reliable choice for the home garden.
- Cate, native to California this M Tetraphylla cultivar is an aggressive growing plant that has some frost hardiness. It is a self-harvesting variety that produces rough shelled, large fruits.
- Dorado, a M. Integrifolia cultivar native to Hawaii has an upright growth habit. Dorado produces a good yield of fruit and is pleasingly cold tolerant.
- James is native to California. A M. Intergrifolia cultivar, James has a vigorous growth habit and can fruit within 3 to 4 years. James is a tall column shaped self harvesting variety that produces medium-sized fruits.
- Keaau is another M. Intergrifolia variety that is native to hawaii. This cultivar produces medium sized fruits and is popular for its vigorous upright growth habit.
- Vista is a California hybrid that produces pink flowers and medium sized fruits. A self harvesting type that forms into a pyramid shape, you can enjoy Vista fruit after 3 years of steady growth.
- Waimanalo is a M. Integrifolia variety that is native to Hawaii. It produces clusters of thick fruits that are so large they sometimes split in half to form twins.
- Integrifolia is an attractive cultivar that produces edible fruit. starr-110331-4416 by Forest and Kim Starr / CC 2.0
A great ornamental plant, if you are growing a macadamia nut tree for the fruit be warned that this is a notoriously low yielding plant. However, there are some steps that you can take to increase the yield. These include:
- Planting more than one tree to increase cross pollination rates,
- Plant good quality grafted trees from productive cultivars,
- Growing lots of pollinator friendly plants nearby,
- Encourage bees and beneficial insects to the garden.
If you are growing in a large area or orchard, interplanting with two or more different cultivars also helps to boost yield rates.
These are tall, wide specimens reaching a mature height of 30 to 40 ft. They can spread almost as wide. If you are planting in a garden, take into account any overhead obstacles such as wires as well as below ground infrastructure such as drains when selecting your planting position.
The root system of the macadamia nut tree is described as “proteoid”. This means that it is made up of compact root clusters that efficiently harvest nutrients from the soil to feed the plants growth.
While this is an ornamentally attractive specimen, for many the main attraction of the plant is the fruit. A healthy and mature macadamia nut tree can produce 30 to 50 pounds of fruits in a year. As the tree ages it becomes more productive.
As the plants age, they become more productive. Macadamia ternifolia by Royal Botanic Garden Sydney / CC 2.0
Despite its productivity, the fruit of the macadamia nut tree is expensive. This is largely because the trees require lots of water, particularly when young to grow and thrive. This makes commercial cultivation expensive. The plants also struggle in frosty positions and if exposed to high winds.
Further complicating the matter, the fruits ripen at different times. This means that the plant can be harvested multiple times during the growing season.
Some varieties self-harvest. This means that the fruits fall to the ground where they can be picked up. Other types retain their fruit on the tree. This means that the fruit must be harvested from the branch.
Adding further expense to commercial production the fruits have hard shells which have to be cracked open without damaging the kernel inside. This, along with processing, packaging and transportation all adds to the cost. Growing your own is a lot less expensive.
Commercial production can be expensive. https://pixabay.com/photos/macadamia-nut-organic-harvest-nuts-912598/
Propagating a Macadamia Nut Tree
Part of the Proteaceae plant family, this is a self-pollinating specimen. This means that it doesn’t grow true from seed. In other words a seed harvested from a macadamia nut tree won’t grow to be a true replica of its parent plant. It may not even set fruit.
Growing from seed can take 10 years before a plant is ready to produce fruit. Instead, a quicker option is to start cultivating from a grafted plant. This provides a little jump start that can cut your wait time for fruit in half.
The following are some of the most common methods of producing new macadamia nut tree saplings.
Air Layered Cloning
Use a sharp knife to strip away some of the bark on a low, pliable branch. The branch is then placed in a growing medium until roots form. Once roots are present the plant can be separated from its parent plant. This process replicates the desirable traits of the parent plant.
Also known as budding this technique requires the scion, or bud, which has desirable traits, is placed in a slit in the branch of a host tree. Here the scion can establish a root system of its own.
Once a new root system is established, the branch can be removed from the parent plant and planted on.
Bud grafting is a labor intensive process which is more suitable for commercial growers than home gardeners.
Grafting a Cutting
This is the process of inserting cuttings from plants with desirable cuttings into sturdy rootstock. This produces a plant with predictable desirable characteristics as well as good disease resistance. A heritage tree such as Hinde H2 is often used as the rootstock.
It takes several years of nursery care for the grafted plant to be established enough to sell.
Rooting a Cutting
A more accessible way to start a plant, this process requires a cutting taken from a young branch. This is dipped in rooting hormone before planting in a potting medium.
The planted cutting is kept in a sheltered position and regularly watered. Eventually roots form and new growth becomes visible.
When substantial growth is visible the cutting can be transplanted to the garden.
Growing from Seed
You can either harvest and sow your own seed or purchase a seedling. Typically seedlings are around 6 inches tall and have a set of true leaves when sold.
Growing from seed produces unpredictable results.
Growing from seed is unpredictable.
To sow your own seed you need a freshly harvested nut. Ideally this should be taken from a local macadamia tree.
Prepare the seed by removing the outer husk. This reveals a smooth, brown shell. Plant the fresh seed as soon after harvest as soon as possible. If you want to store the seed over winter, store in a container filled with sand and potting medium. Soak the stored seeds in water for 2 days before planting.
When you are ready, plant the seed in a pot filled with a well draining potting medium. The pot should be at least 1 ft deep. This gives the roots lots of room to grow into.
Plant the seed roughly twice as deep as the kernel is thick. There is a raised ridge on the kernel. Plant the kernel so that the ridge is parallel to the soil surface.
Cover the kernel with a loose layer of soil and water well.
Keep the soil moist by watering at least once a week. Water until excess moisture pours from the bottom of the pot.
Place the pot in a sunny window. You can also put the pot on a heat mat to encourage germination.
It can take a few months for seeds to germinate.
Young plants should be cultivated indoors before transplanting when they are large enough. Vog injury to leaves of young macadamia plants by Scot Nelson / CC 1.0
Of the methods outlined above, rooting a cutting and growing from seed are most suitable for home growers.
The easiest way to start growing a macadamia nut tree is planting a grafted plant purchased from a plant nursery. This grafted specimen should be a healthy plant. It will have known characteristics and a proven track record of healthy growth, flowering and fruit production.
Where to Plant
Hardy in USDA zones 9 to 11, do not plant these specimens in areas where frost can occur. While some varieties display some cold tolerance, all types struggle when consistently exposed to cold temperatures.
The macadamia nut tree grows best in warm climates including southern Texas, California, Hawaii and Florida.
These plants do best in warm climates. Coraki by denisbin / CC 2.0
Your chosen location should be a sunny spot. The macadamia nut tree tolerates partial sun but does best in full sun. Do not plant in a position that is exposed to high winds.
The soil should be fertile, well draining and slightly acidic.
Before planting use a soil test kit to measure the acidity and nutrient content of the soil in your chosen growing area. The pH level of the soil should ideally measure between 5.5 and 6.5. In addition to the pH level, a soil test also tells you if your soil is lacking in any vital nutrients.
Work in any necessary amendments before planting.
How to Plant
Prepare your planting position as early in the year as possible. Ideally, the planting position should be prepared in early January for a late winter planting. Aim to have your macadamia nut tree planted and settled by the time spring starts.
If you are growing a plant from seed, wait until true leaves have formed and the stem is at least 6 inches tall before transplanting. Remember to harden off your plants before transplanting.
Plants purchased from a plant nursery should be planted as soon as possible. Soak the bare rootstock in a bucket of water while you dig the planting hole.
Dig a large hole in the ground. If you are planting a specimen grown from seed, the hole should be large enough to comfortably hold the root system. To check the size of the hole, place the plant, still in its pot, in the hole. The pot should fit neatly, its lip should be level with the soil.
To plant a larger specimen, dig down twice as deep as the nursery container and twice as wide. This gives the root system room to spread.
Remove the plant from its pot and position in the ground so that the plant sits at the same depth as in the pot. The root crown should be just below soil level. Be careful not to plant too deeply. This can cause transplant shock, meaning that your young plant struggles to settle into its new position.
Backfill the hole, tamping the soil down as you do so to remove air pockets. Soak the soil with a garden hose before tamping down to remove any remaining air pockets before watering again
Continue to water regularly, keeping the soil evenly moist, until the plant starts to produce fresh growth. A collar of soil between 1 to 2 ft tall helps the soil to retain moisture.
After plating is the best time to install some form of support such as a Jevrench Tree Stake kit. This helps to ensure strong upright growth as well as protecting delicate saplings from snapping in a strong wind.
If you are planting a number of specimens, space them at least 25 ft apart. This allows air to circulate freely between mature plants. It also gives the roots lots of room to spread.
Space your saplings out to give them room to grow. starr-080715-9233-Macadamia_integrifolia-row by Forest and Kim Starr / CC 2.0
Caring for a Macadamia Nut Tree
Once new growth is visible and the plant is settled in its home, you can adapt your care routine.
Keep the area beneath the tree clean and tidy. Messy areas can attract insects and rodents.
It is important that you weed the soil regularly. Weeds have a shallow root system when compared to your macadamia nut tree. This means that they find it easier to access moisture and nutrients.
Allowing weeds to flourish not only deprives your plant of vital nutrients it can also have a negative effect on growth and fruit production.
Weed your soil regularly.
After harvest, add a layer of coconut coir mulch to the soil around the tree. This improves moisture retention and deters weed growth.The layer of mulch should start roughly 1 ft from the trunk.
Be careful not to lay the mulch too close to the trunk. This can attract pests.
When to Water
Water is the most important aspect of macadamia nut tree care. During hot, dry periods the plants can require up to 350 liters, around 92 gallons, a week.
Freshly planted specimens should be watered regularly until new growth emerges. After this, reduce watering to once a week unless your garden experiences a period of heavy rain. During periods of heavy rain there is rarely any need to give your plants additional water.
Mature specimens can tolerate a light drought. Extended periods without water harm growth and fruit production.
Keeping plants hydrated can require a lot of water. Building your own rainwater collection system is a great way to reduce your water usage whilst also keeping your plants hydrated.
Collecting rainwater helps to reduce your water usage and keeps your plants hydrated.
Fertilizing Growing Plants
The macadamia nut tree is a slow growing plant. If you amend the soil before planting, it should be nutrient rich enough to support growth for a few months or until the plant is fully settled in its new position.
Around 6 months after planting apply a fertilizer that contains little nitrogen, less than 1%.
Fish emulsion or a citrus mix fertilizer, such as Espoma Organic Citrus-tone fertilizer are both great choices for a growing macadamia nut tree. Apply, as per the instructions on the packet, during the fall and winter months.
A liquid fertilizer is easy to apply and can be incorporated into your watering routine. If using a liquid fertilizer, water the soil all the way to the drip line, this is the perimeter beneath the outermost leaves.
Fertilizing evenly over a large area helps to protect the main stem from fertilizer burn. It also ensures a good distribution of nutrients and encourages the roots to evenly spread out.
As the tree grows, regularly measure the soil to check for nutrient deficiencies. These should be amended as quickly as possible. Allowing the soil to become severely nutrient deficient could cause serious health issues for your plant
With a regular dose of fertilizer, trees can start fruiting from the age of 6. Some varieties can begin fruiting earlier than this.
Organic mulches boost growth and protect roots.
Protecting Your Plants
Young and growing specimens require protection from both winds and frosts. Wind protection when fruits are forming is also necessary to prevent your crop falling from the tree before they ripen.
Gardzen Fabric Frost Jackets can be installed on young and smaller plants when wind or frost is forecast. This protection can be removed as soon as the weather improves.
A layer of mulch can also be used to protect the root system from cold weather.
If you are planting in an exposed position a WANZHU Tree Stake Kit can be used to support the young sapling.
Companion plants should be shallow rooted cover crops. Plants with deeper roots can damage the fragile root system of the macadamia nut tree. They also provide competition for essential nutrients.
Clover is a good companion, adding nitrogen to the soil while helping moisture retention and soil aeration.
To improve pollination rates and increase your fruit yield, pollinator and bee friendly flowers can be planted close by, either in the soil or in planters.
Clover is a good companion plant. Source: https://pixabay.com/photos/clover-leaves-green-plants-foliage-1225988/
Prune established specimens in late winter before any early signs of spring emerge.
Pruning annually helps sunlight to reach all areas of your plant, encouraging growth and flowering. It also helps to promote air circulation around and through the plant. This helps to prevent bacterial problems such as powdery mildew.
Trees that don’t self harvest, or drop fruit, as well as those growing in planters should be pruned down to a manageable height.
Prune your macadamia nut tree with pruning shears. The process is similar to pruning an apple tree.
Prune to promote a single strong trunk and 6 to 8 horizontal branches. These should be spaced evenly along the tree.
Clip away vertical growing shoots. These shoots do not produce fruit and take up valuable energy that could be better used elsewhere by the plant.
Finally, prune away dead or damaged wood.
Common Pests and Problems
If you are growing in the continental United States the good news is that both M. Integrifolia and M. Tetraphylly are not prone to pests and disease. Some pests such as the macadamia nut borer are not a problem in the United States but can be a problem if you are growing elsewhere.
A largely problem-free plant, specimens experiencing extremes of weather or those that are not watered correctly can become vulnerable to problems. Discolored, misshapen or falling leaves as well as damaged bark and fruit falling before maturity are all signs that your plant is unhealthy.
Leaf discoloration can be a sign of disease. Macadamia thrips by Scot Nelson / CC 1.0
Cankers can develop in wounds. These, such as the Phytophthora ramorum fungus can cause the tree to bleed sap and foliage to die. Other fungal infections can affect the leaves or growth of your plant.
Infestations can cause your plant to become unsightly. If left untreated your macadamia nut tree can develop serious problems. Scale insects can damage the branch material while thrips feed on the leaves. Stink bugs can also be a problem.
Many infestations can be treated by applying neem oil to the affected leaves and branches. Your local extension service can help to evaluate your foliage and recommend suitable treatments.
Rodents are attracted to fallen fruit if not harvested and cleared up promptly.
Finally, the macadamia nut tree is not a deer resistant plant. Protect tender young shoots with Yowlieu Mesh Protectors.
How to Harvest
Be warned, not every flower produces a nut. The easiest way to improve the size of your yield is to plant pollinator friendly flowers and encourage bees, butterflies and other pollinators to your garden.
The macadamia nut first forms as a green husk. These turn brown and begin to crack open when ripe. Inside is the edible kernel. When they ripen and form depends on the variety.
Do not try to shake fruit from the tree. This can cause unripe fruit to fall, impacting on later harvests. Instead a long pole can be used to dislodge mature fruits.
Place tarp beneath the tree to gather self-harvesting varieties. Don’t leave the tarp there permanently this can stop water reaching the roots. Water on the tarp can also cause the fallen fruits to rot.
To check the ripeness of your harvest place the macadamia nuts in a bucket of water. Ripe fruits float to the top.
Some fruits fall from the branch when ripe, others remain in place. Source: starr-080715-9230-Macadamia_integrifolia by Forest and Kim Starr / CC 2.0
How to Store and Preserve
After harvest, you can either prepare and eat the fruits fresh or preserve them for use at a later date. The easiest way to preserve your crop is to roast the macadamia nuts.
To prepare your harvest, begin by removing the outer husks. Place your crop on a screen in shallow layers, no more than 2 deep. Air dry for 2 to 3 weeks in a cool dry location. This loosens the kernels.
You can also dry your harvest in a food dehydrator. The kernels are dry when they are crisp to the bite.
Once dry, use a nutcracker to crack the shells and remove kernels. You can now roast the kernels in a single layer at 275 ℉ until golden.
Roasted kernels can be stored in airtight jars or frozen. In a cool dry spot they keep for up to 1 year.
Remove the fruit from the shell before use. Macadamia Nuts by Richard Ashurst / CC 2.0
An ornamentally attractive plant, the macadamia nut tree is a striking addition to the garden. Producing showy flowers and edible fruit, this specimen is a great choice if you want to add interest or shade to a sunny garden.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.