How to grow Walnut in New Zealand

Where to plant

Walnuts grow into very large trees, often 12 to 15 m tall and as wide, so they are best for rural properties and big gardens rather than suburban sections. Plant in full sun in deep, well-drained soil, well away from buildings, drains and vegetable beds.

They like a dry climate with hot summers and real winter chill. They will grow in humid areas, but walnut blight is worse there. Late spring frosts can damage the flowers of early-flowering varieties.

Walnut roots and leaves release a natural chemical called juglone that holds back the growth of many plants nearby, so keep vegetable gardens and fruit trees out of its root zone.

• Northland: not recommended. Winters are too mild for a reliable crop and the humidity brings walnut blight.
• Hawke's Bay, Marlborough, Canterbury and Central Otago: the dry, cold-winter districts suit walnuts best.
• Auckland, Waikato and the Bay of Plenty: trees grow, but choose the most blight-resistant variety you can find.

Choosing a variety

Buy grafted trees of a named variety. They crop in 3 to 5 years, while seedlings take 10 to 15 years and vary in nut quality. New Zealand Tree Crops Association trials in the 1980s identified the main varieties grown here today.

• Shannon: the most blight-resistant variety, does well in most parts of New Zealand, and was the heaviest and most consistent cropper in Tree Crops trials.
• Rex: the most widely planted variety, with some blight resistance and heavy crops of small, tasty nuts that store well. The hard shell keeps rats out but is harder to crack. It does not tolerate wet feet.
• Meyric: a big tree with easy-to-open, sweet nuts that store well. It flowers late, which suits frost-prone areas, but it is prone to blight and dislikes wet soil.
• Walnuts carry male and female flowers that often open at different times, so planting two varieties gives better pollination and crops.

How to plant

1. Plant in winter while the tree is dormant. Dig in compost over a wide area first, and on clay add gypsum.
2. Dig a hole twice as wide as the root ball and the same depth. Tease out any circling roots.
3. Set the tree at the depth it grew in the nursery, backfill and firm gently.
4. Make a ring of soil around the root zone to hold water, water in well, and stake young trees on windy sites.
5. Mulch with bark or wood chips, keeping it away from the trunk.

Watering and feeding

Water young trees deeply once or twice a week through dry spells for their first few summers, especially from bud burst through spring. Established trees have deep roots and usually need watering only in long droughts.

Feed young trees with a fruit tree fertiliser in spring and summer, and top up compost or mulch once or twice a year.

Pruning and care through the year

• Walnuts need little pruning. Train young trees to a single strong leader with well-spaced branches, and after that prune every few years to remove dead, crossing or low branches.
• Prune in late summer rather than spring, as walnuts bleed heavily from cuts made when the sap is rising.
• Keep grass and weeds away from young trees, which compete for water.

Harvesting

Nuts fall from March to May. The first nuts to drop often still have bits of husk on them and are frequently poor, so wait until nuts are falling cleanly out of their green or blackened husks. Gather them off the ground quickly, before rats, possums and birds do.

Spread the nuts out in the sun for two or three days to dry, then store them in mesh or onion bags hung high in a dry, airy shed, out of reach of rats. Nuts in the shell also freeze well. Wear gloves when handling husks, as they stain skin brown.