Tree · Proteaceae
Macadamia
Macadamia integrifolia
Give it warmth, deep soil, and a pollination partner, and the macadamia becomes the quiet anchor of a warm-climate garden.
Full sun
Every 7–14 days
USDA 9–11
30–50 ft · 9.1–15.2 m
Overview
A macadamia is the kind of tree that gives a warm-climate property its sense of permanence. This large evergreen from the Proteaceae family, native to the subtropical forests of southeast Queensland, grows into a broad, shading presence of 30 to 50 feet (9 to 15 m) that reads as a landmark rather than a specimen. Through winter and spring it hangs long racemes of white to pinkish bloom, and from late summer into winter it drops its hard-shelled nuts across the ground beneath.
As a fixture of the garden, it belongs to the mild, frost-free life of USDA zones 9 to 11. It wants an open, sunlit position, deep and rich acidic soil, and the steady generosity of at least 50 inches of rain or irrigation a year. There is one point of manners to observe: as a Proteaceae, it takes little phosphorus, so the heavy feeding routine most gardens run will not suit it and should be eased right back.
Living with a macadamia is a long, unhurried relationship. A grafted tree settles in and begins bearing after about 2 to 5 years, and most cultivars keep better company with a second compatible partner nearby, which turns a handsome tree into a productive one. The reward is a shaded corner of the garden and a home-grown supply of a luxurious nut, with one clear caveat for any household that includes a dog: the nuts are not safe around them.
Care
The short version: give it an open, sunny position, deep rich acidic soil, and a frost-free corner sheltered from wind. Keep it evenly watered, feed it lightly with a low-phosphorus blend, and set a second cultivar nearby so the flowers carry through to nuts.
Light
Placed in full sun, the tree carries the fullest flowering and crop, though it accepts a little partial sun in a mixed setting. The more open the position, the more the canopy has to give.
Water
It asks for steady moisture, underwritten by at least 50 inches of rain or irrigation a year, with a deep soak during dry spells every 7 to 14 days. An established tree carries some drought with grace, but let it go thirsty and both the nut set and the quality quietly fall away.
Soil
Give it deep, rich, well-drained acidic loam at a pH of 5.0 to 6.5. Depth is as much the point as fertility, since a tree of this stature settles a substantial root system into the ground.
Temperature
Its comfort lies in subtropical warmth, roughly 32°F to 95°F (0°C to 35°C). Frost marks it, and long spells above the top of that range scorch the leaves and interrupt the nuts, so a sheltered spot pays dividends.
Humidity
Average humidity of 50% to 70% flatters it. Still, damp air at bloom invites blossom blight, so an airy canopy does more for the tree than the reading on a gauge.
Feeding
Feed through spring and summer while it grows, but keep to a balanced blend that is low in phosphorus. As a Proteaceae, macadamia is sensitive to phosphorus, and an excess yellows the new leaves and takes the tips, so a restrained hand is the elegant choice.
Pruning
Shape a young tree to a single central leader and clear the low, crossing, or dead branches in late winter. As it matures the tree needs only light corrective attention to hold its form.
Repotting
This is a tree for open ground, so repotting scarcely enters the picture. Pot up a young grafted tree only until it takes its place in the field, then plant it out and let the garden do the rest.
Size & spacing
360–600 in (914–1524 cm) tall
When to plant
The macadamia keeps to a warm, frost-free calendar, and its year has a gentle rhythm. Settle a grafted tree into the garden in spring once the cold has passed, enjoy the fragrant bloom that drifts through winter and spring, and let the nuts come in as they ripen and fall from late summer into winter.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to spring if growing from seed, though grafted trees are strongly preferred
- Plant: Spring, after all danger of frost has passed
- Harvest: Fragrant white to pinkish flowers on long racemes in winter to spring; nuts ripen and drop from late summer through winter
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
When a macadamia falters, it tends to show in the leaves, the flowers, or the crop, and the story usually traces back to feeding, weather, or a missing pollination partner. Read the signs below and respond early. A young tree given a considered start rarely troubles you with the rest.
New leaves yellow with dying tips
New leaves that pale while their tips die back tell of excess phosphorus, which macadamias and the wider Proteaceae simply cannot process as other plants do. A soil or leaf test settles the question. Withdraw the high-phosphorus feed, move to a balanced low-phosphorus blend, and flush the soil with a deep watering where the level runs high.
Fix:
- Stop applying high-phosphorus fertilizer
- Switch to a balanced, low-phosphorus fertilizer
- Leach the soil with deep watering if phosphorus is excessive
Nuts drop early and few hold on the tree
A tree that blooms freely yet keeps almost nothing usually stands alone or belongs to a self-sterile cultivar, and poor cross-pollination is the heart of it. Heat above 95°F (35°C) through flowering and nut fill deepens the loss. Set a second compatible cultivar nearby, keep bees at work among the flowers, and hold steady moisture with wind shelter while the nuts develop.
Fix:
- Plant a second compatible cultivar nearby
- Support bee activity for pollination
- Provide steady moisture and wind protection during nut development
Flower racemes brown and collapse
Blossom blight is a fungus that settles in when the air stays humid and the flowers stay wet, and the long racemes discolor and fall apart in muggy weather. Open the canopy through thoughtful spacing and pruning, and where the trouble returns year on year, apply an approved fungicide at bloom.
Fix:
- Improve air circulation through proper spacing and pruning
- Apply an approved fungicide at bloom if blight is recurrent
Burnt edges on sun- and wind-hit leaves
Sustained heat above 95°F (35°C) and hot, drying winds scorch the leaf margins, and the damage gathers on the most exposed foliage. Raise a windbreak or shelter belt and keep the soil moist through the heat. A frost-free position that does not bake keeps the problem at bay.
Fix:
- Provide wind protection or shelter belts
- Maintain soil moisture during heat
- Site in a frost-free but not excessively hot location
Toxicity
At the table the kernel is a pleasure, a fine snack for anyone in the house, yet for a dog the same nut is a genuine danger. Even a few macadamias can leave a dog weak, unsteady, and unable to stand within hours, and the reason still eludes the science. Keep every nut, raw or roasted or fallen underfoot in the garden, well beyond a dog's reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
No poisoning has been recorded in cats, yet the nut has not been shown safe for them either. Treat it as off-limits and call a vet should a cat manage to eat one.
Dogs Severe
Here lies the real danger. Even a few nuts can leave a dog weak in the hind legs and unable to walk, with vomiting, a high fever, muscle tremors, an unsteady wobble, and a flattened mood, usually within 12 hours.
Horses Caution
Macadamia toxicity remains unstudied in horses, so the nuts and any windfall are best kept out of reach until more is known.
Rabbits Caution
There is no record of how rabbits react, and a rich, fatty nut suits them poorly regardless, so it should not be offered.
Livestock Caution
Cattle, goats, and sheep have not been tested for this toxin, so fence them from a fruiting tree lest they graze on dropped nuts.
Birds Caution
The effect on birds is unknown, and the high fat content does them no favors, so keep the nuts from poultry and pet birds alike.
People Edible
For the people of the house the roasted kernel is a welcome, perfectly safe snack. The toxin troubles only dogs, not the humans who share the garden and table.
Keep fallen nuts, raw or roasted nuts, and any nut-containing foods away from dogs; even small amounts can trigger signs.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
The choice of macadamia comes down to two species and the hybrids and cultivars drawn from them. These are the names worth knowing as you plan the planting.
Smooth-shell (Macadamia integrifolia)
It carries a smooth, rounded shell and stands as the main commercial type grown across Hawaii.
Rough-shell (Macadamia tetraphylla)
A separate species marked by a pebbled, rough shell and often pink new growth, prized as a parent in several hybrids.
'Beaumont'
A pink-flowered cross of integrifolia and tetraphylla that has become a favorite for backyard plantings.
'Kau' (HAES 344)
A Hawaiian smooth-shell cultivar the University of Hawaii chose for its high yield and fine kernel quality.
Companions
What grows around a macadamia matters less than what grows beside it. A second cultivar is the partner that counts, while thirsty turf under the canopy only gets in the way.
Plant near
second compatible macadamia cultivar: Cross-pollination between cultivars improves nut set and yield.
Keep apart
shallow-rooted turf grass under the canopy: Competes for surface moisture and nutrients and complicates harvesting fallen nuts.
How to propagate
A macadamia can be started two ways, though only one delivers a dependable crop. Grafting is the orchardist's route and the sound choice for a garden; seed is for rootstock, breeding, and the patient.
GraftingModerate
Warm months once seedling rootstocks are about pencil thick · Grafts take in a few months; trees begin bearing in about 2-5 years
Grafting is the graceful and reliable route, since it yields trees true to the cultivar. Undertake it in the warm months once the seedling rootstocks reach pencil thickness; the graft knits within a few months, and the tree comes into bearing in about 2 to 5 years. Match scion to rootstock with care, and never cross a smooth-shell with a rough-shell type by mistake.
SeedModerate
Sow fresh, mature nuts in late winter to spring · Germinates in 1-2 months; seedlings may take 7-12 years to fruit and are variable
Starting from seed suits rootstock or breeding more than a dependable crop. Sow fresh, mature nuts in late winter to spring and they sprout in 1 to 2 months. The price is patience and chance, for seedlings vary and can take 7 to 12 years to fruit.
Myths
A few macadamia nuts are harmless to dogs.
Even a small handful can set off macadamia poisoning, with signs surfacing within 12 hours. Any amount is a vet call, never a wait-and-see.
A single macadamia tree will produce a full crop on its own.
Cultivars range from self-fertile to nearly self-sterile, so a solitary tree is a gamble. A second compatible cultivar lifts both nut set and yield, which is why an orchard never rests on one tree.
Seed-grown macadamias come true to the parent and fruit quickly.
Seedlings are unpredictable and can take 7 to 12 years to bear. Orchards plant grafted trees instead, since these hold true to the cultivar and come into fruit in about 2 to 5 years.