Macadamia
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At-A-Glance InformationThis species of evergreen trees needs full sun and regular water to perform and produce well. These trees reach 30-40 feet tall and almost as wide. Leaves are glossy, leathery and narrow, and white to pink flowers appear in winter and springtime. Common names for these trees include Queensland Nut, Bush Nut, Maroochi Nut, Bauple Nut, and Hawai'i Nut, and their edible nuts are cultivated in many parts of the world. Take care when planting these trees in the landscape, as the nuts are poisonous to dogs.
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macadamia Species and Varietals
The genus Macadamia includes four species and is a member of the plant family Proteaceae. The genera Lasjia and Virotia contain many species that were once considered to be a part of the Macadamia genus. Macadamia trees grow well in zones 9, 16, 17, 19-24, H1 and H2. To find your zone, click here: Zone Map.
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Macadamia Hybrid Varieties These trees are crosses between Macadamia integrifolia and Macadamia tetraphylla. The hybrid varietal 'Beaumont' is one of the best varieties for California, and produces medium to large nuts. 'Cooper' has smaller nuts, and 'Vista' produces small to medium-sized nuts with very thin shells. |
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Macadamia integrifolia (Smooth Shell Macadamia, Bush Nut, Queensland Nut, Bauple Nut, Nut Oak) This species is commercially grown, a popular choice in Hawai'i and it also does well in Southern California. Leaves have smooth edges and nuts ripen from the end of fall through springtime. Popularly grown varieties of this species include 'Kakea', 'Kau', 'Keaau', 'Mauka', and 'Purvia'. |
Did You Know? Macadamia nuts, although edible for humans, are toxic to dogs!
The toxicity of these nuts depends on the dog's weight, size, and overall health factors, but the minimum toxic dose is about 1 nut per 2.2 pounds of body weight. Signs of poisoning include weakness, vomiting, difficulty walking and lack of muscle control, increase in body temperature and abdominal pain, among others. If your dog has ingested macadamia nuts, you should remove the nuts from their reach, monitor your dog for symptoms, and call a pet poison helpline (ASPCA: 888-426-4435). Most dogs recover completely within 48 hours without treatment.
The toxicity of these nuts depends on the dog's weight, size, and overall health factors, but the minimum toxic dose is about 1 nut per 2.2 pounds of body weight. Signs of poisoning include weakness, vomiting, difficulty walking and lack of muscle control, increase in body temperature and abdominal pain, among others. If your dog has ingested macadamia nuts, you should remove the nuts from their reach, monitor your dog for symptoms, and call a pet poison helpline (ASPCA: 888-426-4435). Most dogs recover completely within 48 hours without treatment.
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Macadamia ternifolia (Small-Fruited Queensland Nut, Gympie Nut) This species is considered threatened with extinction in its natural range, and is native to Queensland, Australia. These plants form multi-trunked trees that can reach up to 26 feet tall at maturity. |
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Macadamia tetraphylla (Rough-Shell Macadamia, Bauple Nut, Prickly Macadamia, Rough-Shelled Bush Nut) This species performs well in inland California areas, and has a more open growth habit than other species. Leaves are spiny, and nuts have thin shells, ripening from autumn to the middle of wintertime. Popularly grown varieties include 'Burdick', 'Cate' and 'Fenton'. |
Caring for and pruning macadamia Trees
These productive nut trees thrive in full sun exposure, and require between 6 and 8 hours of direct sunlight each day for best flowering. Adequate sunlight is crucial for both the health of the tree and its productive capacity. These trees typically prefer subtropical to tropical climates, though there are cultivars that can tolerate cooler climates, as well. They are frost-sensitive, and young trees especially will need some protection from cold temperatures. If growing these trees in a cooler climate, make sure they are planted in a spot in the landscape that is relatively protected from drying winds and cooler temperatures. They prefer well-draining soil that is acidic to neutral (with a pH of between 5.5 and 6.5). They do well in loamy soils, but will tolerate a wide range of substrates, as long as they drain well. If local soils are overly clay or compacted, make sure to amend the planting area with plenty of sand and/or organic material. Water both young and established trees regularly. Ensure that the soil does not become saturated; allow soil to dry out between deep waterings of mature trees, and provide additional waterings during periods of heat and drought. In dry conditions, this typically translates to deep watering once a week. Waterings can be reduced in wintertime when trees are dormant. Apply a thick layer of mulch around new plantings and maintain it for the life of the tree. This will help to increase soil moisture retention, suppress weed growth, and regulate soil temperatures.
These trees prefer to grow in rich soils in order to produce good harvests of nuts. Balanced fertilization is essential, though these trees are also very sensitive to over-fertilization. Apply a generous layer of organic compost each year in springtime to support the season's flowering and foliage growth. If trees seem to be struggling or they are not producing well (or if local soils are particularly poor), these trees may benefit from a feeding with a balanced, slow-release fertilizer. Trees that are young (a few years old) should not be fertilized. Macadamia trees generally don't require much in the way of pruning. Occasional cleanups of dead, damaged, diseased or crossing branches can help to maintain a handsome shape and increase airflow through the canopy. The best time to prune these trees is in late wintertime to early spring. Macadamia nut trees typically produce suckers at their base; these growths can be removed at any time.
Harvesting Macadamia Nuts
Mature trees will begin producing nuts around 7-10 years of in-ground growth. Grafted trees will be able to produce sooner. Healthy adult macadamia trees will produce around 30 to 50 pounds of nuts by 10 years of age, and the amount gradually increases as trees mature. Nuts are typically harvested once their outer husk splits open and reveals the nut inside. Nuts will fall to the ground at this point, and be collected. Nuts can also be cut off of trees in summer and fall (sometimes into winter, depending on where they are grown), when they are becoming mature. After harvesting, separate cracked nuts from whole ones. Any that are whole will need to lay out to dry and open on their own. Dry ripened whole nuts in shade for about 2 weeks when weather is dry. This will reduce moisture content and prevent them from going bad. De-husk cracked nuts as soon as possible. If nuts are not cracking, they can be placed in an oven between 100 and 150 degrees Fahrenheit for 12 hours. They should be easy to husk at this point. They should have a chocolate-brown inner husk when ready (inner husks are white when unripe), and edible husked kernels will float when dropped into water. Husks can be removed with vice grips, hammers, or nutcrackers. Discard any nuts that are cracked or discolored. They can be stored in a cool, dry area in a container for between 2 to 3 weeks. Roast nuts as soon as practicable.
These trees prefer to grow in rich soils in order to produce good harvests of nuts. Balanced fertilization is essential, though these trees are also very sensitive to over-fertilization. Apply a generous layer of organic compost each year in springtime to support the season's flowering and foliage growth. If trees seem to be struggling or they are not producing well (or if local soils are particularly poor), these trees may benefit from a feeding with a balanced, slow-release fertilizer. Trees that are young (a few years old) should not be fertilized. Macadamia trees generally don't require much in the way of pruning. Occasional cleanups of dead, damaged, diseased or crossing branches can help to maintain a handsome shape and increase airflow through the canopy. The best time to prune these trees is in late wintertime to early spring. Macadamia nut trees typically produce suckers at their base; these growths can be removed at any time.
Harvesting Macadamia Nuts
Mature trees will begin producing nuts around 7-10 years of in-ground growth. Grafted trees will be able to produce sooner. Healthy adult macadamia trees will produce around 30 to 50 pounds of nuts by 10 years of age, and the amount gradually increases as trees mature. Nuts are typically harvested once their outer husk splits open and reveals the nut inside. Nuts will fall to the ground at this point, and be collected. Nuts can also be cut off of trees in summer and fall (sometimes into winter, depending on where they are grown), when they are becoming mature. After harvesting, separate cracked nuts from whole ones. Any that are whole will need to lay out to dry and open on their own. Dry ripened whole nuts in shade for about 2 weeks when weather is dry. This will reduce moisture content and prevent them from going bad. De-husk cracked nuts as soon as possible. If nuts are not cracking, they can be placed in an oven between 100 and 150 degrees Fahrenheit for 12 hours. They should be easy to husk at this point. They should have a chocolate-brown inner husk when ready (inner husks are white when unripe), and edible husked kernels will float when dropped into water. Husks can be removed with vice grips, hammers, or nutcrackers. Discard any nuts that are cracked or discolored. They can be stored in a cool, dry area in a container for between 2 to 3 weeks. Roast nuts as soon as practicable.
Propagation
Macadamia trees can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your tree, follow the instructions below:
Propagating Macadamia by Cutting
Propagating Macadamia by Seed
Propagating Macadamia by Cutting
- Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
- In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 6 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
- Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
- Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.
Propagating Macadamia by Seed
- Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
- Harvest your seeds. Mature trees that are at minimum between 12 and 15 years old will produce full harvests of nuts, and trees as young as 5 years can produce smaller crops. Harvest nuts and remove their outer husks. Viable, ripe nuts will have chocolate-brown interior husks. If they are not ready yet, the interior husk is greenish-white. Do not roast nuts to remove their outer husk, as this will destroy seed viability and they will not germinate.
- Soak seeds in lukewarm water for 24 hours before sowing.
- Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 7-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
- Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.
Harvested nuts with their husks still on.
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Macadamia fruits contain just one nut each. After harvesting and de-husking, they can be sown.
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Problems and Pests
Macadamia nut trees, although generally pest- and disease-resistant, can be affected by the following pests and diseases:
- Macadamia Nut Borer & Tropical Nut Borer
- Rats and Mice
- Anthracnose
- Husk Spot
- Raceme Blight
- Trunk and Stem Canker
Gallery
Macadamia trees are cultivated commercially in Hawaii, Australia, Southeast Asia and South Africa.
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Each flower spray produces about 20 nuts.
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Macadamia nut cookies are a popular baked good.
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There are about 3,000 acres of Macadamia trees in the state of California.
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Macadamia trees are large, but can be kept more compact through regular prunings.
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These trees are pollinated by a wide variety of insect species.
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Videos
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Grow these expensive nuts for yourself.
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Learn about the Macadamia nut industry in this informative video.
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How to grow a Macadamia nut tree.
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Efforts are being made to save these Australian natives.
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Resources
https://www.epicgardening.com/macadamia-nut-tree/Wikipedia: Macadamia
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 426, Macadamia
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