Words & Photos: Hannah Zwartz
To grow walnuts, you need to think big. The massive trees can reach 25m high, with branches spreading 15m wide. Their root systems, likewise, are deep, meaning they also need space below ground level, ideally in deep, well-drained soil. Added to this, walnuts crop best with a partner nearby for pollination, so you may need to find room for not just one, but two such giants.
Given space, however, the investment is well worthwhile. A mature walnut tree can produce 30kg or more of nuts a year (currently retailing at $12.90 per kilo in the shell) with a productive lifespan of 100 years or more.
I know several quarter-acre sections where gardeners have found room for a walnut, and a neighbour has one near enough to help with pollination. Maybe would-be walnut growers need to think communally – a walnut tree could be a neighbourhood asset, and it’s perhaps surprising they aren’t more commonly grown as shade trees in parks and schools. There’s a beautiful specimen at Paekakariki Playcentre, shading the sandpit in the heat of summer and providing nuts to collect and eat, as well as autumn leaves to pile up and play with. Paraparaumu Domain also has some good specimens – but the best ones I’ve seen are in the old settlements around Banks Peninsula in Canterbury. Probably originally planted by French settlers, they tower majestically among the old apples and quinces, dropping their bounty generously year after year.
Most of the walnuts grown in New Zealand are hybrids and variants of Juglans regia, the English or Persian walnut. This originates in Central Asia, where summers are hot but not humid, and winters can be very cold. Walnuts have been cultivated for thousands of years, spreading all along the Silk Road from China through to Syria and the rest of the Mediterranean, and distributed by the Roman Empire throughout Europe (their botanical name Juglans comes from the Latin Jovis glans, meaning the nuts of the god Jupiter). The biggest growers today are in the Balkan countries.
Walnuts play a part in many Mediterranean cuisines, in baked goods ranging from baklava to walnut/coffee cakes, where the nuts replace flour for a rich, moist texture. They’re also great in salads, adding crunch, flavour and essential fatty acids.
Popular varieties in New Zealand include ‘Wilson’s Wonder’, giant in size and easily cracked; ‘Meyrick’, a large tree with easily opened nuts that flowers later – good for areas with late frosts; and ‘Diana’, a newer variety bred near Wanganui. ‘Rex’ bears much smaller nuts, which are densely nutritious but harder to crack – this can actually be an advantage if rats are a problem and you are unable to harvest nuts daily. All these named varieties are grafted, so the trees don’t come cheap. But walnut trees grown from seed will be of varying quality, with some bearing good crops but others more of a miss – and you may not find the difference until after about 10 years when trees should come into full production.
When nuts first drop, the flesh can be milky and a little bitter, sweetening as they dry over the next few weeks (spread them out on racks if possible in a dry place). Damp weather at harvest time (May) can be a problem, especially if nuts are left on the ground, as it’s liable to lead to mildew in the nutmeat.
Walnut trees don’t need much pruning once mature – in fact they don’t particularly like being cut. Newly planted trees can be helped along into a good shape by pinching out the leader and growing tips over summer to encourage more branching. They will need good staking, or, better still, plant in a well-protected area without strong winds, especially salt winds, which burn the leaves.
One strange quality of walnut trees is their allelopathy – like some eucalyptus species, they chemically inhibit the growth of other species nearby. This is done through the chemical juglone, found throughout the plant but particularly prevalent in the roots, and especially in Juglans nigra, the American black walnut (most trees in New Zealand are grafted onto J. regia, apparently less allelopathic). The apple family is said to be especially sensitive to this. Walnut leaves can still safely be added to compost, however, as the composting process breaks down the juglone.
Immature walnut fruits have a bright green husk, which darkens as they ripen. The young fruit, before the shell develops inside, can be pickled (they turn black during this process) or made into liqueurs by steeping them in spirits. The immature fruits can also be used to make a powerful dye for hair, skin or fabric – you might want to wear gloves when collecting walnuts as the skins, even when mature, can stain your hands a deep brown.
And when the time comes to cut down a walnut tree, the timber is among the world’s most valuable, its dense grain and deep colour highly prized by woodworkers.