Tree · Proteaceae
Macadamia
Macadamia integrifolia
Give it warmth, deep soil, and a pollination partner, and the macadamia hands back rich nuts for the trouble.
Full sun
Every 7–14 days
USDA 9–11
30–50 ft · 9.1–15.2 m
Overview
So what is a macadamia, really? It's a big evergreen in the Proteaceae family that comes from the subtropical forests of southeast Queensland. Give it years and it grows into a broad, heavy-canopied tree of 30 to 50 feet (9 to 15 m), then puts out long strings of white to pinkish flowers through winter and spring. The hard-shelled nuts ripen and drop from late summer into winter.
This one's for warm, frost-free ground in USDA zones 9 to 11. It likes full sun, deep and rich acidic soil, and a good drink of at least 50 inches of rain or irrigation a year. Here's the twist that trips people up: it's a Proteaceae, and those can't handle much phosphorus, so the heavy feeding you'd give most fruit trees actually hurts it. Odd, but easy enough to work around.
Growing macadamias takes patience, no way around it. A grafted tree needs about 2 to 5 years before it bears, and most cultivars want a second compatible partner close by to set a decent crop. Worth it, though, because you end up with your own supply of one of the richest nuts going. Just a heads-up if there's a dog in the house: those nuts are genuinely dangerous to them.
Care
The short version: full sun, deep rich acidic soil, and a frost-free spot out of strong wind. Keep it evenly watered, feed it lightly with a low-phosphorus blend, and put a second cultivar nearby so the flowers actually turn into nuts.
Light
Macadamias crop best in full sun, though they'll take a bit of partial sun without much fuss. The more light the canopy grabs, the more flowers and nuts it can carry.
Water
Keep the tree in steady moisture and figure on at least 50 inches of rain or irrigation a year. Water it deeply during dry spells, every 7 to 14 days. An established tree shrugs off some drought, but the second it goes thirsty, nut set and quality start to slip.
Soil
Plant it in deep, rich, well-drained acidic loam at a pH of 5.0 to 6.5. Depth counts just as much as fertility here, because this is a big tree and it sends down a serious root system.
Temperature
It's happiest in subtropical warmth and holds up somewhere between about 32°F and 95°F (0°C to 35°C). Frost hurts it, and long stretches above the top of that range burn the leaves and stall the nuts.
Humidity
Average humidity of 50% to 70% works nicely. Damp, still air during bloom is what brings on blossom blight, so honestly, good airflow through the canopy matters more than the number.
Feeding
Feed it through spring and summer while it's actively growing, but grab a balanced blend that's low in phosphorus. Being a Proteaceae, macadamia is sensitive to phosphorus, and too much yellows the new leaves and kills the tips.
Pruning
Train a young tree to a single central leader and take out low, crossing, or dead branches in late winter. Once it's mature, it only needs the odd light corrective cut.
Repotting
This is a ground tree, so repotting barely comes into it. Pot up a young grafted tree only until it's ready for the field, then plant it out and let it be.
Size & spacing
360–600 in (914–1524 cm) tall
When to plant
Macadamias run on warmth and won't take any frost, so timing matters. Plant a grafted tree out in spring once the cold's fully gone, keep an eye out for those fragrant flowers through winter and spring, and pick up the nuts as they ripen and drop 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
Most of the time, macadamia trouble turns up in the leaves, the flowers, or the nut crop, and it usually comes back to feeding, weather, or a missing pollination partner. Match what you're seeing below and jump on it early. Get the basics right on a young tree and you'll rarely deal with the rest.
New leaves yellow with dying tips
If the new leaves go yellow and the tips die back, that's usually too much phosphorus, which macadamias and the rest of the Proteaceae just can't deal with like other plants. A soil or leaf test will tell you for sure. Cut the high-phosphorus feed, switch to a balanced low-phosphorus blend, and if levels are high, flush the soil with a good deep watering.
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
Blooming great but keeping almost nothing? That's usually a lone tree or a self-sterile cultivar, and poor cross-pollination is the main reason. Heat above 95°F (35°C) during flowering and nut fill only makes it worse. Plant a second compatible cultivar nearby, keep the bees busy at the flowers, and hold steady moisture with some wind shelter while the nuts fill out.
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 moves in when the air stays humid and the flowers stay wet. You'll spot the long racemes going discolored and falling apart in muggy weather. Open up the canopy with decent spacing and pruning, and if it keeps coming back year after year, spray 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
Long heat above 95°F (35°C) and hot, drying winds scorch the leaf margins, and it shows up worst on the most exposed foliage. Put up a windbreak or shelter belt and keep the soil moist through the heat. Pick a frost-free spot that doesn't bake, and you'll mostly keep this from happening.
Fix:
- Provide wind protection or shelter belts
- Maintain soil moisture during heat
- Site in a frost-free but not excessively hot location
Toxicity
The kernel is a great snack for people, so no worries there. Dogs are the problem, and it's a real one: even a few macadamias can leave a dog weak, shaky, and unable to stand within hours, and nobody's figured out why yet. Keep every nut, raw or roasted or fallen on the ground, well out of a dog's reach.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
Cats haven't shown any poisoning, but that doesn't mean the nut's proven safe for them either. Treat it as off-limits and ring a vet if a cat gets hold of one.
Dogs Severe
This is the big one. Even a few nuts can leave a dog weak in the hind legs and unable to walk, plus vomiting, a high fever, muscle tremors, an unsteady wobble, and a flat, low mood, usually within 12 hours.
Horses Caution
Nobody's studied macadamia toxicity in horses, so it's best to keep the nuts and any windfall out of reach until there's more to go on.
Rabbits Caution
There's no record of how rabbits handle it, and a rich, fatty nut isn't good for them anyway, so don't offer it.
Livestock Caution
Cattle, goats, and sheep haven't been tested for this toxin, so fence them off from a fruiting tree so they can't graze on dropped nuts.
Birds Caution
What it does to birds is anyone's guess, and the high fat content does them no favors, so keep the nuts away from poultry and pet birds alike.
People Edible
Good news for everyone at the table: the roasted kernel is a popular snack and perfectly safe for people. The toxin only bothers dogs, not the humans sharing the house.
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
It really comes down to two species and the hybrids and cultivars that came out of them. Here are the names worth knowing before you plant.
Smooth-shell (Macadamia integrifolia)
It's got a smooth, rounded shell and it's the main commercial type grown across Hawaii.
Rough-shell (Macadamia tetraphylla)
It's a separate species with a pebbled, rough shell and often pink new growth, and it's prized as a parent in a bunch of hybrids.
'Beaumont'
It's a pink-flowered cross of integrifolia and tetraphylla that's become a real favorite for backyard plantings.
'Kau' (HAES 344)
It's a Hawaiian smooth-shell cultivar the University of Hawaii picked for its high yield and good 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
There are two ways to start a macadamia, but only one gives you reliable nuts. Grafting is how the orchards do it; seed is more for rootstock, breeding, and folks who don't mind waiting.
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's the way to go, because it gives you trees that stay true to the cultivar. Do it in the warm months once your seedling rootstocks are about pencil thick, and the graft knits within a few months while the tree comes into bearing in about 2 to 5 years. Match scion to rootstock carefully, and whatever you do, don't cross a smooth-shell with a rough-shell type by accident.
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
Growing from seed is really more for rootstock or breeding than for dependable nuts. Sow fresh, mature nuts in late winter to spring and they'll sprout in 1 to 2 months. The catch? It takes patience and a bit of luck, since 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 kick off macadamia poisoning, with signs showing up inside 12 hours. Any amount is a vet call, not a wait-and-see.
A single macadamia tree will produce a full crop on its own.
Cultivars run all the way from self-fertile to nearly self-sterile, so one tree is a gamble. Planting a second compatible cultivar bumps up both nut set and yield, and that's exactly why orchards never bank on a single tree.
Seed-grown macadamias come true to the parent and fruit quickly.
Seedlings are a roll of the dice and can take 7 to 12 years to bear. Orchards plant grafted trees instead, since those stay true to the cultivar and start fruiting in about 2 to 5 years.