Thinking about walnuts

New Zealand Walnut Growing Information Pack

Updated: September 2020

This information pack will help you decide whether walnut growing is for you. Whether you are thinking of purchasing an existing walnut orchard, or planning to develop one yourself, we hope the information will provide useful guidance.

We are assuming that you are at the initial stage of gathering information, so we have included basic notes about the soil and climate you would need to grow walnuts. You’ll also find information on shelter, irrigation and other practical issues. Part 2 of this information pack tells you about the wider walnut industry, including processors, propagators and grower organisations – in particular the New Zealand Walnut Industry Group. We are a very cooperative network of growers, propagators and processors and we would like you to be part of it.

For more detailed information about walnut growing see the New Zealand Walnut Growers’ Manual, available from the NZ Walnut Industry Group. You can purchase a hard copy – contact Anna Morris ([email protected]) or visit our website, www.walnuts.org.nz

Part 1     The practicalities of walnut growing

Climate

A dry climate — such as that along the east coasts of both the North and South Islands — is preferable for commercial walnut production. Currently, Canterbury is home to a large fraction of New Zealand’s walnut orchards. It is possible to grow walnuts in high humidity climates, but the danger of walnut blight and other diseases is much greater.

High temperatures during summer are ideal. The upper limit is reached in the walnut growing areas of the San Joaquin Valley, California, where temperatures frequently soar into the high 30s and above, and sunburn is a problem. We seldom push that limit in New Zealand, and, indeed, are at the lower end of the acceptable summer temperature range. Walnut trees don’t grow as fast in our cooler temperatures, but the quality of our nuts is high.

Walnuts need some winter chilling, and temperatures down to —10°C pose no problem in the winter, when the trees have no leaves. However, young shoots, leaves, catkins and flowers can be damaged by even light frosts during October and November. As the trees grow, the risk lowers somewhat for the higher parts of the tree. Every few years, growers in Canterbury and Otago experience reductions in their crops due to frost, but yields are still sufficient to be viable.

There are two climatic factors in New Zealand that create significant problems. The first is wind, which we discuss in the section on shelter. The second is the wildly fluctuating weather during our spring and autumn. It is common for a warm spell in early spring to prompt bud burst, which may be followed over the next few months by a series of strong winds, hail, driving rain, and frosts — any of which can damage the soft new growth and disrupt pollination of flowers. There is not much you can do, except protect small trees from frost as far as possible and provide shelter for walnut trees of all ages.

Soil

The number one soil requirement is good drainage. Walnuts are very sensitive to inadequate oxygen in the soil. If their roots sit in stagnant water for more than a couple of days they are starved of oxygen and the trees can die.

If you are buying a property, it is best to view it in the winter, just after a good period of rain, to see whether there is any standing water. If this is caused by a temporary plough pan you may be able to break it up, but if the poor drainage is a natural feature of the soil (e.g. a clay layer) the land may not be suitable for walnuts. Determine the soil type on the property and its layers of clay, silt, sand, gravel and loam, considering both topsoil and subsoil. You can get soil information for most of the flatter productive land in New Zealand from https://smap.landcareresearch.co.nz 

Also find out the height to which the water table can rise. If it comes within three metres of the surface, particularly during the growing season, it could present a risk to mature walnut trees.

Walnuts will grow more vigorously in a fertile soil, so the orchard will reach full production earlier. However, high quality soil is usually expensive, so you must trade off the higher land price against the earlier production. A loam or silt loam soil is ideal for walnut growing. A sandy loam is also good but will not hold water and nutrients as well as a silt loam.

It is possible to gradually restore both the fertility and structure (drainage) of soil that has been heavily cropped in the past. Grass, clover and deep rooting plants growing (undisturbed by cultivation) on the orchard floor will increase the soil’s organic content, which will in turn increase its capacity to hold nutrients, worm population, aeration, and structure. Some growers spread commercially made compost over the soil which will also improve soil structure. You can add fertilisers to address any major nutrient deficiencies but be aware of the limitations of your soil type. It is recommended that an initial soil test be done to check the soil pH and any nutrient deficiencies. Once the trees are planted, an annual leaf test is advised to show what nutrients are needed for the trees each year. ARL and Hill Laboratories carry out these tests.

Shelter

In most areas of New Zealand, shelter is essential for good growth and productivity. Though you may read of the Americans and the French planting walnut orchards without shelterbelts, and the English recommending the walnut as a shelter tree, bear in mind that they are not operating in the same windy conditions that we are. You will need to think carefully about the size of your blocks, your shelterbelt species (with their final height, rate of growth, deciduousness, and other characteristics), and your irrigation and weed control for shelterbelts. A rule of thumb with shelter trees is every metre of shelter height gives 10 metres of wind protection horizontally.

When buying land for planting walnuts, a block with mature shelter (external and internal) already in place is likely to be more expensive than “bare land”, but it is worth weighing up whether the price differential will be offset by earlier production. If you are starting from a bare block, it will take about three years before your newly-planted shelterbelts will have grown sufficiently to provide protection to young walnut trees, depending on the growing conditions and the shelter species you use. Popular shelter species include poplar (‘Crows Nest’), alder and Leyland cypress.

Irrigation

Water availability is an important factor in choosing a site. Walnut trees are unlikely to die from water stress in New Zealand, but lack of water will greatly affect growth and production, and the nuts will not grow to full size. In most of the drier east coast climates recommended for walnut growing, rainfall during the summer period is not sufficient to balance evapo-transpiration, and irrigation will be needed. Even so, you should weigh the value of using irrigation against the cost of installing, maintaining and operating it.

The most common system used in walnut orchards is sprinkler irrigation, where each tree has its own micro-sprinkler. Dripper irrigation is an option (at least in the first few years) but root development may be restricted to the smaller area covered by the dripper.

When you are looking for a property, find out whether it has an irrigation consent, or whether you can get one. It is also worth assessing the suitability of any existing irrigation equipment for your purpose, e.g., bore size and drawdown, pump size, presence of sand in the water etc. As a rough guide, in the summer, average evapo-transpiration is likely to be around 5mm per day across your full orchard area. Across a 10-hectare orchard, for example, 5mm of water equates to a volume of 500 cubic metres. Depending on your soil type, irrigation equipment and the weather, you may be irrigating your trees every few days to every two weeks. Make sure the supply and pump are capable of delivering the volume of water you need.

You will find useful advice from professional irrigation suppliers and engineers. Another valuable resource is the Irrigation New Zealand website (https://www.irrigationnz.co.nz).

 It is recommended that you have an irrigation system designed by a professional irrigation engineer.

Pests and diseases

We are fortunate in New Zealand to have few walnut pests and diseases. It means that walnuts are one of the less difficult crops to grow in a restricted spray regime. Walnut blight and Phytophthora root rot are the main diseases. Hares can be a problematic pest when the trees are young.

Walnut blight:

Blight is the only disease which New Zealand walnut growers need to spray for routinely. It is a bacterium and is typically managed with copper-based sprays often mixed with dithiocarbamates. Some copper sprays may be used in restricted amounts by organic growers. The spraying season is from September until Christmas and the frequency and number of sprays increases with rainfall, humidity and temperature. In a dry season with low humidity, two sprays may be sufficient to effectively manage blight, whereas in a wet season with high humidity as many as 8 sprays may be required. Incomplete management of blight will result in loss of yield (since blight affects the nuts) and some reduction in vegetative growth (since blight affects the new season’s growth) but it will not kill a tree because it does not affect old growth.

Phytophthora:

This is a soil-borne fungus that attacks and rots the roots of a tree; it is the destruction of the root system that kills the tree. Phytophthora thrives in over-wet soils. It is difficult to eradicate the fungus from the soil and root system once it is established there. Thus, walnuts should be grown in free-draining soil and not over-watered. Whilst some walnut trees growing in wet conditions may survive, overall, the odds are much better in free draining soils.

Hares/Rabbits:

Both pests can fatally damage young trees and heavy rabbit pressure can inflict significant damage on older established trees. The safest option is to use tree-guards to protect young trees. Hares and rabbits cause damage in quite different ways. Hares practice careful ’estate management’ and tend to remove novel features in their estate such as newly planted trees. They will bite off the trees, rather than eating them. Rabbits, on the other hand, seek somewhere to sharpen their teeth and can cause significant damage to tree trunks which may subsequently break in a strong wind. They may also chew on smaller irrigation pipe and fittings, causing leaks.

Nuts and/or timber?

The walnut veneer on the dashboards of the rich and famous, and the quoted prices for walnut gunstocks are powerful arguments for growing timber. However, it’s worth keeping two things in mind. First, a walnut tree is unlikely to be large enough to mill until it is around 45 years old. Second, the generally-preferred species for timber is the black walnut (Juglans nigra), rather than the edible nut species, Juglans regia (English walnut). Note also that, like most high value hardwoods, walnuts grow poorly on the clay hill-sides where we commonly put our Pinus radiata.

Grafted walnut trees (J. regia) will start producing walnuts almost immediately, though we recommend that you remove the nuts over the first two or three years to allow the vigour to go into tree growth. Many growers remove the lower branches of trees (gradually working up to 1.5‒2 m). This is mostly so that they can drive machinery under the trees, but it also provides a “second string to the bow”. If the trees have been well pruned to a high quality butt log, then timber harvest may eventually be a reality.

Cultivars

In the 1980s, members of the New Zealand Tree Crops Association had the foresight to begin walnut selection trials. They collected samples of high-performing walnut trees from around New Zealand, tested the nuts for quality (that’s taste and suitability for commercial growing and processing), grew trial trees, and recorded the yields. Two of the selected cultivars that emerged from those trials have become the basis of the fledgling walnut industry in New Zealand. They are ‘Rex’ (also known as 152) and ‘Meyric’ (also known as 1199/4). ‘Rex’ tends to be a smaller tree with smaller walnuts, but is higher yielding and less prone to blight disease. ‘Meyric’ grows into a larger tree and produces nuts that are easier to process.

More recently, the New Zealand Walnut Industry Group imported three new high-performing cultivars from overseas: ‘Howard’, ‘Tulare’ and ‘Lara’. We are currently trialling them in New Zealand, and expect them to do well here.

Planting grafted trees of good cultivars ensures that you have a high quality, consistent product that is already in demand. Seedling trees are a great deal easier to produce and therefore cheaper to buy, and you can sell the nuts from these non-grafted trees, but (depending how and where you sell them) the price is usually lower because the nuts are inconsistent in physical characteristics and taste.

It is important to plant at least two chosen varieties to ensure good pollination.

Time frames until first harvest

Walnuts are not a quick-return crop. Though grafted trees are often able to bear straight away (as one-year old trees), it is usual to remove the nutlets in the early years so that the trees’ vigour will go into developing the canopy.

Your maximum production will come when the full land area is covered by tree canopies. Growth of the trees to achieve full canopy cover will be quicker on a good soil and with good shelter. Another way of achieving canopy cover earlier is to plant the trees at closer spacings, though you will need to be ready to thin out trees in later years when the canopy becomes too dense. You should weigh up the cost of the extra trees against the returns from early fruiting.

With good soil and shelter, careful fertiliser and irrigation management, and a typical 7 × 7 m tree spacing, you might expect full canopy cover by around 15 years old, at which point the production should be approaching 2.5 tonnes per hectare. But in poorer growing conditions or with wider tree spacings, full canopy cover can take much longer to achieve, and production per hectare will be much lower for that extended period.

Time commitment in setting up and managing a walnut orchard

Because walnut growing (at commercial scales) is a new industry in New Zealand, and the trees take a while to come into full production, most growers work in other employment while setting up their walnut orchards. The orchard size that is manageable depends on your employment hours and other responsibilities, however, orchard sizes commonly range from 4 to 10 hectares, with a few as large as 20 to 50 hectares. The typical orchard is small by international standards but we expect that, as the industry becomes more firmly established, orchards will become larger.

Set-up tasks in the first few years include:

  • Shelter belt establishment. You may need to plant several thousand trees on a 10-hectare block.
  • Ordering your walnut trees. The full process of producing grafted trees takes several years, so it’s best to get in contact with a propagator well in advance of when you will need the trees.
  • Irrigation installation. You may need to have a bore drilled and purchase and install irrigation equipment.
  • You will need to dig or auger holes for planting, then place shelter boxes around trees to protect them from wind and hares.
  • You will need to prune the young trees to encourage a branch structure for optimum mechanical strength and production of fruit.

On-going management tasks include mowing, weed control for both shelter trees and walnut trees, irrigation, pruning, and spraying to protect your trees against disease.

Harvesting

Depending where you are in New Zealand and what cultivars you are growing, nuts typically begin to fall in late March and harvest goes through until early May. If you have a small walnut orchard, or your trees are young, you will be able to pick up your crop with just simple manual equipment like the very good nut roller (https://www.lourdangrove.co.nz/Products/Lourdan-Grove-products/Nut-Harvester) or Bag a Nut harvester (https://baganut.com/). Once your production passes a couple of tonnes, you may need to consider a mechanical harvester – there are various options depending on the volume of your crop. Go to walnut.org.nz for information on harvesters.

You will need to sort your walnuts – to remove leaves, sticks, stones and bad nuts – and wash them. Your crop then needs to be dried and, again, there are various equipment options depending on the size of your operation. It is very important for walnuts to be dried correctly so that they can be stored (in-shell) for a number of months, or even a full year. Not drying walnuts sufficiently will result in nuts becoming mouldy in storage. 

Equipment needed

As noted above, the equipment you need depends on your crop volume. Most growers will have a tractor with a mower and a spray rig. Larger growers approaching full production will have a mechanical harvester and possibly a tree shaker, tip-trailers, a full washing/sorting line (in a processing shed) and a dryer. They will also have wooden bins and vermin-proof storage for their crop. Smaller growers or those at an earlier stage of tree growth tend to accomplish these steps with smaller or simpler equipment.

Part 2     The walnut industry

Selling your walnuts

The prospects for marketing high quality walnuts and value-added products in New Zealand are very positive.

Currently, 90% of walnuts sold domestically are imported from the USA, China or India, however, the quality is generally low with nuts often being old and not tasty. It creates a significant opportunity for New Zealand growers. We are able to grow an extremely good product in New Zealand, and our top cultivars have outstanding appearance, taste, storage ability and nutritional value. More and more New Zealanders are discovering the freshness and taste of New Zealand grown walnuts. There is also a greater awareness of walnuts as a healthy food option as they are high in Omega 3 (proven to lower the incidence of heart disease), and fibre which aids bowel health. Walnuts are a versatile plant-based protein used in sweet and savoury dishes. Because walnuts are a long lived, large tree that absorbs a considerable amount of carbon over its life, it is one of a few agricultural crops that in the operation of growing walnuts there are very low carbon emissions. All these benefits add up to high consumer acceptance and demand.

There is almost no export of walnuts from New Zealand. This may be a future possibility, though we need to be aware that in most other countries, growers are paid a commodity level price for their nuts. We would need to aim for niche markets with value-added products as many other New Zealand horticultural industries do.

Most New Zealand growers sell their crop to a local processor, though others do their own marketing, including gate sales, online sales or farmers’ markets. Note that a Food Safety Programme and Certification is required if you are planning to sell processed/value-added walnut products.

The largest processor is the grower-owned Walnuts New Zealand Co-operative Ltd, based in Canterbury. Its website is https://walnutsnz.co.nz, and its products are marketed under the retail brand Trickett’s Grove: https://www.trickettsgrove.nz. There are also other smaller processors, including Uncle Joe’s based in Marlborough: http://www.unclejoes.co.nz. You can contact processors directly to find out about supplying them.

Growers and processors sell walnuts to consumers as kernel pieces for snacking and baking, or in-shell, or as products such as walnut oil, flour, dukkah or walnut paste. To find out more about walnut products, recipes and who is selling them around New Zealand, see https://www.walnutsplease.nz

Propagators

Walnuts are very tricky to propagate. Rootstocks are grown from seed, wrenched from the ground at two years old, and then the scion wood of the chosen cultivar is bench-grafted onto the rootstock during winter dormancy. The graft union requires a period of heating to be successful. Because of this long and difficult process, you should aim to order your young trees several years in advance of when you wish to plant.

Walnut propagators of whom we are currently aware are listed below (please let us know if we have missed any propagators!):

  • Peninsula Tree Nursery, Prices Valley, Canterbury, (03) 329 0045
  • River Terrace Nurseries, Brightwater, Nelson, [email protected], (03) 542 3317

The New Zealand Walnut Industry Group

NZWIG is the industry organisation for New Zealand walnut growers. Its roles are to:

  • Encourage discussion and learning amongst growers by

–      holding field days to enable learning from experts and other growers, and so that growers can benchmark their progress against others

–      arranging social events to enable contact and discussion with like-minded people

  • Instigate research and development to improve the knowledge of walnut growing in New Zealand
  • Disseminate information on current knowledge and best practice in walnut growing via:

–      this information pack for new growers

–      the NZWIG newsletter

–      the New Zealand Walnut Growers’ Manual, which is a comprehensive guide to walnut growing in New Zealand

–      our website containing research reports, field day notices, chatzone etc.: www.walnuts.org.nz.

To join the New Zealand Walnut Industry Group, go to our website (www.walnuts.org.nz) or contact Anna Morris, email: [email protected]

A full annual subscription for NZWIG is $100 per orchard and includes newsletters and field days. Any additional person associated with the orchard may join as a personal member for $20 per year. If you are joining NZWIG for the first time, we will give you a 50 per cent discount.

The research projects that NZWIG is currently undertaking are:

  • Benchmarking – to compare performance in a range of orchards. The project will enable us to establish performance benchmarks and give us a better understanding of what growth rates and yield to expect from our orchards. Information and orchard data entry are via the website.
  • Cultivar trial planted 2005 ‒ trialling nine promising New Zealand walnut selections on four sites around the country.
  • Cultivar trial planted 2011 – trialling three new imported cultivars, plus four further New Zealand selections.
  • Fungi found in walnuts after harvest – what causes this and what to do about it.

Past projects also include:

  • Import of three new cultivars (two American varieties and one French variety) from Tasmania through strict quarantine and testing (2009‒2011).
  • Sustainable methods for blight management: alternative spray types and timing were investigated (2001‒2007). See reports and recommendations on the website.
  • Pruning/Training experiments: We assessed a range of training strategies for young walnut trees and published the results (2004‒2007).

The New Zealand Tree Crops Association

Commercial walnut growing in New Zealand was first initiated by members of the New Zealand Tree Crops Association (NZTCA), and they carried out the early trials of cultivars and growing methods. NZWIG grew out of NZTCA in the early 2000s once walnut growing started to become more commercial. Many walnut growers are members of both NZWIG and NZTCA. The organisation covers a wide range of tree crops, with specifically walnut-related information available at: https://treecrops.org.nz/crops/nut/walnut.

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New Zealand Walnut Industry Group