How to Grow Macadamia

Macadamia integrifolia · Also called: Macadamia nut, Queensland nut, Bush nut, Maroochi nut, Nuez de macadamia, Makadamia, Hawaii nut

Macadamia trees in an old orchard on Maui, with dense rounded crowns of dark glossy evergreen foliage.

Photo: Forest & Kim Starr, CC BY 3.0 (Wikimedia Commons)

Macadamia is the only Australian native plant grown as a major food crop around the world, and it is one of the highest-value nuts there is. Australia, South Africa, Kenya, China, Guatemala, Malawi, Viet Nam, Brazil and the United States all produce it, and in Kenya and Malawi in particular it is an important smallholder crop grown among other trees rather than in plantations. It takes years to come into bearing and then produces for decades. What decides a grower's income, more than anything in the field, is the two days after the nut falls.

Growing Macadamia, Stage by Stage

1. Get the land ready — Deep well-drained soil out of the wind, with room for a large long-lived tree.
2. Choose your trees and planting material — Grafted trees of two or more named kinds, chosen for your climate.
3. Plant the trees — Plant at the start of the rains, stake against wind, and mulch widely from the first day.
4. Water — Steady water through flowering and nut fill, and never any standing water.
5. Weeds, feeding and pruning — Mulch instead of digging, feed without phosphorus, and prune only lightly.
6. Flowering and nut set — Long hanging strings of small flowers, of which only a very few become nuts.
7. Watch for trouble — Bugs that spoil the kernel from outside, a borer in the nut, and rats on the ground.
8. Harvest — The nuts fall when they are ready. Collect them off the ground often, and never shake them down.
9. De-husk, dry, store and sell — Get the green husk off within about a day, then dry slowly, because this is where the money is made or lost.

Common Problems & Troubleshooting

If you see: A buyer grading your nuts down badly, or cracked kernels that are discoloured, soft or smell stale, from a crop that looked fine when collected.

It likely means: The green husks were left on too long. A husked nut heats within hours and the kernel inside starts to spoil, and nothing done afterwards recovers it.

Do this: De-husk within about twenty-four hours of collecting, and sooner in hot weather.

If you see: Trees yellowing, browning at the leaf tips and going backwards after a general fertiliser was applied.

It likely means: Phosphorus. This family's roots are adapted to soils with very little of it and are damaged by the amounts in ordinary fertiliser mixtures.

Do this: Stop applying general high-phosphorus fertiliser to macadamia.

If you see: Trees growing poorly in an orchard where the ground underneath is regularly ploughed, hoed or kept bare and clean.

It likely means: The feeding roots have been destroyed. They sit in the top few centimetres in dense mats, and cultivation cuts them off.

Do this: Stop ploughing and hoeing under the canopy entirely.

If you see: Nuts that look perfectly sound from outside but whose kernels are marked with sunken brown spots when cracked.

It likely means: Sucking bugs fed on the young nuts and pierced the shell while it was still soft. The damage is inside and invisible until cracking.

Do this: Walk the orchard through nut fill and look for shield-shaped bugs on the young nuts.

If you see: Nuts collected from under the trees that are mouldy, gnawed or already sprouting.

It likely means: They lay on the ground too long. Fallen nuts take up moisture from wet ground and are found by rats.

Do this: Collect every one to two weeks through the season, and more often in wet weather.

If you see: Trees carrying enormous numbers of flower strings and setting very few nuts.

It likely means: Partly normal, since only a small share of flowers ever becomes a nut. If it is severe, it usually means only one kind was planted, or bees are absent.

Do this: Plant at least two different named kinds that flower at the same time.

If you see: Bearing trees leaning badly or blown flat after a storm, with roots lifted out of the ground.

It likely means: Shallow roots and a heavy crown. Macadamia roots do not go deep and the tree is top-heavy when loaded.

Do this: Plant a windbreak on the exposed side, before the orchard if you can.

Yield & Market Value

Growing the crop is only part of the job. The last part is knowing what a normal harvest looks like where you are, and knowing what your nuts are worth before you agree a price with anybody.

Remember It This Way

If you forget every other page of this guide, keep these lines. They are the whole crop, in order, short enough to carry in your head.

Grafted trees, and at least two different kinds.
Two kinds that flower together, or the set is poor.
No phosphorus fertiliser. This family's roots hate it.
Never plough or hoe under the tree. The roots are at the top.
Mulch wide instead, out to the edge of the branches.
Shallow roots and a heavy crown. Shelter it from wind.
Never shake the tree. A fallen nut is a ripe nut.
Collect every week or two. Wet ground spoils them.
Husk within a day. That is where the money is.
Dry slowly in shade until the kernel snaps, not bends.

Test Yourself: Identification

What does a macadamia tree look like?

What do the flowers look like, and why are so few nuts set?

What is the green covering, and when does it come off?

Honest Limits of This Guide

Timings are given in years from planting and in months from flowering rather than in named months, because macadamia is grown in both hemispheres and in the tropics at altitude. Count from your own rains.
Which kinds suit your altitude and your heat, and which flower together, differ sharply by country and this guide cannot name them for your area. A licensed nursery or your extension office can, and the decision cannot be changed once an orchard is planted.
Yield figures assume mature trees from about the tenth year and are not comparable with a young orchard. What a grower is actually paid depends on kernel recovery rather than tonnage, which no yield figure shows.
This guide names no chemical treatments. Nothing should be applied during flowering because the crop depends on bees, and the losses that matter most here come from husking and drying rather than from anything sprayed.
Macadamia nuts are known to be poisonous to dogs, although they are entirely safe for people. Farm households often have dogs around the drying racks, and it is worth keeping nuts and husks where they cannot reach them.

Sources

GBIF Backbone Taxonomy species-match record for Macadamia integrifolia Maiden & Betche — Global Biodiversity Information Facility (GBIF), Copenhagen (source)
EPPO Global Database — Macadamia integrifolia (EPPO code MCDIN) — European and Mediterranean Plant Protection Organization (EPPO), Paris (source)
FAOSTAT crops and livestock products — production data for nuts, and FAO work on macadamia in eastern and southern Africa — Food and Agriculture Organization of the United Nations (FAO), Rome (source)
Macadamia integrifolia (macadamia nut) — CABI Compendium datasheet — CABI, Wallingford (source)

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