How to grow Macadamia in New Zealand

Where to plant

Macadamias grow well where citrus grow well: warm, sheltered, frost-free sites, ideally near the coast. They need shelter from strong and cold winds, as the trees have brittle branches and relatively few lateral roots. An ideal site is a gentle north-facing slope with deep, free-draining sandy or volcanic soil, which lets cold air drain away.

Young trees, up to two or three years old, are frost tender, so avoid frost pockets and wrap the trunks of young trees in frosty spells. Mature trees tolerate light frosts. The soil should drain freely and sit around pH 5.5 to 6.5; heavy clay gives yellowing, stunted trees, and macadamias do not tolerate salty soil or water.

• Northland, Auckland and coastal Bay of Plenty: the main growing districts. Plant from September to November in a sheltered, frost-free spot.
• Inland Waikato and Bay of Plenty: marginal. Plant in October or November in a warm, sheltered spot and use frost cloth while young. Coastal Bay of Plenty suits it best.
• Central North Island: marginal. Plant in November in a sheltered spot and wrap young trees for their first winters.
• Nelson and Marlborough: marginal. Plant in October or November in a warm, sheltered coastal spot and use frost cloth while young.
• Canterbury, Otago and Southland, and Central Otago: too frosty for macadamias.

Choosing a variety

Plant a named, grafted variety rather than a seedling, which may take much longer to crop and give poorer nuts. Beaumont is a hybrid that has long been the most common variety in New Zealand, both commercially and in home gardens, with heavy crops of large nuts and pink, scented flowers. Its nuts hang in clusters and usually need picking, as they tend not to drop.

Macadamias vary from self-compatible to largely self-sterile, and cross-pollination between different varieties gives much better crops. If you have room, plant two different grafted varieties; smaller self-pollinating dwarf types are available for small gardens.

How to plant

1. Plant in spring, or autumn in frost-free spots, choosing a sheltered, sunny site.
2. Enrich the soil with compost, and on clay fork in gypsum and organic matter. Dig a hole twice as wide as the root ball and no deeper.
3. Tease out the roots so they make good contact with the soil, as some potting mixes stop roots growing out. Plant at the same depth, with the graft union above the soil.
4. Water in well, form a ring of soil to hold water and mulch, keeping mulch off the trunk.
5. Stake the tree for its first few years.

Watering and feeding

Young trees need regular water and are easily stressed by drought. Established trees still need deep watering in long dry spells, which helps prevent nut drop.

Feed three or four times a year with a balanced fertiliser in small amounts. Avoid heavy phosphorus and do not over-lime, which can cause iron deficiency, shown by yellowing between the veins of new leaves.

Pruning and care through the year

• Prune young trees to build a strong framework, removing narrow-angled branches that can split.
• As the tree matures, open up the centre to let light in and keep it to about 3 to 4 m high for easier harvesting.
• Remove dead or damaged branches.
• Wear gloves when working in the tree; the leaves are spiny.

Harvesting

Nuts take about seven to eight months to mature after flowering. Beaumont is usually ready from about August. To test, pick a few full-size nuts, remove the green husks and check the inside of the husk: when it is dark brown, harvest the lot. Some other varieties drop their nuts when ripe, so gather them from the ground every few days.

Remove the green husks within about 48 hours. Dry the nuts in their shells in an onion bag in an airy, sheltered, rat-proof place for six to eight weeks, shaking the bag now and then. Well-dried nuts crack more easily; use a macadamia cracker or a vice. In-shell nuts keep for a long time in a dry, airy, dark place.