Walnuts

  • Overview

    Overview

    Walnuts are one of the oldest tree foods known to man, dating back to 7,000 BC. There are several species of walnut but the one most familiar to Australia, in backyards and commercial plantations, is the English or Persian walnut (Juglans regia). The species is thought to have originated in Central Asia (Persia) and through trade, became established throughout the Middle East and Europe.

    The tree is large and spreading in habit, growing slowly to about 25 metres tall, long-lived and deciduous. It produces fruit that has a green leathery husk, containing a hard wrinkled shell. The kernel of the nut, or nutmeat, is made up of two halves, the appearance of which resembles a brain.

    The kernels have a wide variety of uses as a food, and may be eaten raw, toasted or pickled; prepared with sweet or savoury flavourings as a snack; and used whole or chopped in bakery goods, breakfast cereals, salads, soups, meat dishes, confectionery and ice-cream. Oil, flour and meal are also produced from walnut kernels.

    Although walnuts had been grown in Australia for over 100 years, the industry remained small and production in 2002 was 150 tonnes (in-shell). Research in Victoria, reported in 2000, showed that production could be increased through applying amelioration techniques to  shallow, poorly-structured soils; irrigating to meet water requirements by using soil moisture monitoring techniques, and using grafted trees and new high yielding varieties. The new varieties introduced could bear fruit in their first year and mechanical harvesting and commercial yields were possible by about years 4–6, however, full production was not reached until years 10–12.

    From the 1990s onwards several changes occurred within the industry. The Australian Walnut Industry Association undertook to investigate a means of industry expansion and developed a fee-for-service consultancy as a means of generating R&D funds for industry advancement; also several large walnut plantations were established. As at 2011–12, in-shell production had increased to around 6,000 tonnes. Extensive plantings by corporate interests around 2010 are predicted to  lift future production levels to around 11,000 tonnes by about 2016. Based on current plantings, ninety per cent of national production will be from one company. As of 2010–11, there were 174 walnut growers in Australia.

    The interests of walnut growers and promotion and development of the industry is conducted on behalf of the industry by the Australian Walnut Industry Association.

    Facts and figures

    • The walnut tree most familiar to Australia, in backyards and commercial plantations, is the English or Persian walnut (Juglans regia)
    • Walnut trees are a temperate species, requiring distinct cold and warm periods through the year
    • While modern varieties of walnut bear fruit within their first few years, it takes 4–6 years to produce a harvestable quantity and 10–12 years for the tree to reach full production
    • The work load for walnut growers is intensive during spring and autumn, but as  the trees are dormant through winter they require little attention during these months
    • About 3,000 hectares are planted to walnuts in Australia, with one company accounting for almost 90% of production
    • There is growing consumer demand for walnuts overseas and domestically, believed to be in response to publicity of results of nutritional studies that demonstrate the health benefits of walnuts and the expansion of cultural influences on food via the media.
    • Market opportunities for new growers are influenced by scale of production and ability to meet market demand, with export markets requiring significant volumes and domestic markets seeking fresh ‘direct from the grower’ product

    Production status

    As at 2014, the area planted to walnuts in Australia is about 3,000 hectares, with around 2,200ha belonging to one company with operations in Tasmania and New South Wales. Australian production, as at 2013, was about 8,000 tonnes in-shell but this is expected to increase to over 13,000 tonnes when all current plantings reach full production by about 2016.

    By volume, the key production regions are the Riverina in New South Wales and the east coast of Tasmania. However, walnuts are also grown throughout Victoria, in cooler regions of southern New South Wales around Adelaide and the Riverland, and in south west Western Australia.

    As at 2010–11, it was reported that there were 174 walnut growers in Australia, managing about   929,000 trees. The industry comprises family farm operations of small, sometimes older orchards and large, new orchards that are managed by a few companies, where orchards are a combination of joint venture, investor funded, private ownership or company-owned entities.

    Map of current and potential growing regions

    Click map to enlarge

     

  • Uses

    Uses

    Walnuts are a nutritious snack food sold as whole nuts for cracking or as kernels. The kernels may be value-added through pickling and flavourings for consumption as a sweet or savoury snack. Kernels are also used whole or chopped as an ingredient in savoury foods, bakery goods, breakfast foods, soups, salads, meat dishes, confectionery and ice-creams.

    Walnuts may also be pressed to extract oil, which is generally used in salad dressings. After oil extraction, the remaining kernel may be toasted and ground to produce walnut flour. Alternatively the whole kernel can be ground to make walnut meal. It is also possible to produce walnut milk by blending the nuts with water at high speed.

    As with many nuts, walnuts are recognised for a range of nutritional and health benefits. Walnuts contain vitamins, minerals, healthy polyunsaturated fats, antioxidants, fibre and arginine; but their main claim is as an excellent source of omega-3 fatty acids. As part of a healthy diet, walnuts can help reduce the risk of heart disease and type 2 diabetes, and help with weight management.
  • Production Requirements

    Production Requirements

    Growing regions

    Walnuts require a temperate climate, with about 600–800 hours of chilling below 7°C, temperatures that do not exceed about 38°C and low humidity, consequently the tree is cultivated commercially throughout southern Australia.

    Traditional small-scale orchards are found in Gippsland, in the central regions and the north east of Victoria; in the southern highlands and central tablelands of New South Wales, in the Adelaide Hills and Riverland of South Australia and in south west Western Australia.

    Large walnut plantations are located on the east coast of Tasmania, in the Goulburn Valley of Victoria, in the mid-Murray Valley, South West Western Australia and in the Riverina of New South Wales.

    Soil type

    Historically, it was recommended to grow walnuts on deep, well-drained soils, with a soil pH greater than 6.0. However, commercial production in Australia now occurs on a wide range of soil types, from deep alluvial soils of river valleys to clay soils of the riverine plains. Good site preparation, advanced agronomy and variety development have overcome limitations of some of the ‘new’ environments in which walnuts are now growing in Australia. 

    Climate

    Walnut is a deciduous tree that requires distinct cold and warm seasons. It grows best in a temperate climate, with about 600–800 hours of chilling below 7°C each year and maximum temperatures that do not exceed about 38°C. Development of new production systems since the 1990s has seen the expansion of the walnut industry into environments once thought too hostile.

    In a rain-fed system, in the Great Dividing Range, good production can be achieved on annual rainfall of 1,000mm, however back-up irrigation is advisable to ensure the crop has water at the critical development and production stages. Under irrigation on the riverine plains, the water use target for mature walnuts is 12 ML/ha per season.

    Showery weather in spring causes blight and excessive heat periods in summer can cause sunburn, both resulting in decreased nut yield. Frost in mid to late spring, which is the flowering period, can affect nut set and yield for the season.

    Varieties

    There are hundreds of recognised varieties of the species Juglans regia that have been developed around the world, especially in France and the United States of America (California). Variety development has been based on many characteristics including leaf-out time, maturity, shell thickness, hardness of the shell, kernel colour, flavour and disease resistance.

    Varieties planted in Australia include Chandler, Howard, Tulare, Serr, Vina, Lara and Ashley, most of which are Californian varieties. French varieties planted in Australia include Franquette. New growers should select varieties on the basis of marketing options and suitability to the climate of the orchard location. For example, Chandler and Tulare are grown for their light coloured kernels.  Chandler is grown in areas prone to spring frosts as it leafs-out later in the season, as does Franquette.

    Walnut is a cross-pollinating plant, therefore at least two varieties must be planted to ensure good nut set. It is recommended that pollinator varieties are planted in each orchard to ensure good pollination.

    Variety recommendations should be sought from other growers or specialist horticultural nurseries.

     Planting and crop management

    Walnut orchards are established by planting selected cultivars that are grafted onto a robust rootstock, such as the American black walnut (Juglans nigra), Californian black walnut (Juglans hindsii) or a walnut hybrid. The planting pattern will be determined by soil type, topography and machinery to be used. In traditional orchards, often where soil profiles are deep, trees were planted to a grid as large as 15 x 15 metres. As production has become more intensive and operations are highly mechanised, trees may be planted closely together (6m rows and 3m intervals) and be managed as hedgerows (the ‘Tatura’ system).

    On more shallow soils, the planting row may require ripping and hilling. As with all long-term plantings, soil tests should be carried out several months before planting, so soil pH, soil structure and nutrient levels can be corrected ahead of planting. Planting ideally occurs in late winter or early spring. Mulching and weed control are important at planting time to maximise moisture and nutrient availability to the young trees.

    Walnut orchards will require ongoing nutrient management and fertiliser programs can be based on estimation of nutrient removal rates, soil tests and/or leaf tissue analysis.

    Depending on location, walnuts may require regular irrigation to maintain sufficient water supply to the tree. Soil moisture monitoring systems, such as tensiometers or capacitance probes, can be used to estimate water requirements effectively and efficiently. Mulching can be used to conserve soil moisture on newly planted trees.

    In newly planted orchards, trees are pruned manually to train the trees into the desired shape, as well as to maintain healthy growth on the tree and keep the canopy open with good airflow. As the orchard matures, pruning may be done manually or mechanically depending on the layout and size of the orchard. Mechanical pruning may commence in a hedgerow orchard after 5–7 years, when the trees are strong enough to be managed with pruning saws.

    Pruning is required every 3–4years, depending on growth rates of the trees. Ideally, canopy management should aim to intercept 70–80% of sunlight falling to the ground and maximum tree height should not exceed 80% of the row width. It is important that the tree canopies do not touch across the rows. Trees pruned to the central leader system or pyramid-shaped trees have better light interception, even as the trees age.

    Detailed information on the management of walnut orchards is available for purchase to members of the Australian Walnut Industry Association.

    Weeds, pests, and diseases

    Weeds compete with newly planted trees for water and nutrients, therefore weed control before planting is important, as is mulching of the rows after planting. In a well-maintained mature walnut orchard, the inter-row area is mown regularly to assist with access to the trees and planting rows are mulched or sprayed with herbicide.

    Australian walnut growers face very few pests and diseases, unlike their overseas counterparts. Growers will spray their orchards in spring as the nuts start to develop, to prevent walnut blight. Individual trees may also succumb to phytophthora and require treatment. Sunburn damage can be lessened by spraying the nuts with Kaolin (a white clay) for sun protection.

    Cockatoos are a significant pest for walnut growers in some regions, as they may strip new buds and will damage the green fruit on the tree or remove it entirely, from the time the fruit appears through to maturity when the fruit opens and the nuts are developed. Control measures include gas guns, kites, balloons and deterrent sprays, all of which must be used in rotation as the birds will become conditioned to just one approach. Depending on local and state regulations, growers may be permitted to use firearms for scaring birds or for culling birds attacking the crop. 

     

  • Infrastructure Requirements

    Infrastructure Requirements

    The infrastructure and equipment required to establish and maintain a walnut orchard, would include:

    • cultivator or deep-ripper to prepare planting row
    • irrigation system, including a water source (dam, river, creek or bore), power, pump, timer, piping and under-tree sprinklers, drips or micro sprinklers
    • tractor
    • trailer
    • slasher if orchard floor is grassy
    • fertiliser spreader
    • boom sprayer, spray tank or spray dome for herbicides and sprayer for insecticides and fungicides
    • hand-operated pruning tools or mechanical pruning saw
    • mechanical tree shaker
    • harvester
    • equipment for removing husks and washing nuts
    • racks and fans/driers
    • storage facilities.
    • Grader
    • Bagging or box filling machine.

    Contract services may be needed for some operations, particularly site preparation, harvesting and processing, and present an option to reduce capital expenditure. However, it is important to be confident that the services will be available at critical times.

    It is anticipated that two people could manage 1,000 trees for most of the year but as the orchard reaches full production, casual labour may be required at harvest time.

  • Harvesting & Processing

    Harvesting & Processing

    Walnuts are ready for harvest in autumn – specific timing will be influenced by location and variety. The nuts can mature on the tree over a few weeks, therefore there can be several harvests per season.  In some orchards, a plant growth regulator is used to advance ripening of all nuts so that they can be harvested at the one time to reduce labour and machinery costs.

    The nuts are ready to harvest when the inner membrane between the kernel - called packing tissue - changes from a pale colour to a brown colour. This stage is called packing tissue brown (ptb) and the kernel is mature and light in colour. The timing is usually close to the green outer husk splitting open but it is quite common for the nuts to reach ptb before the hull is split. Once the nuts have fallen, they will start to deteriorate unless they are quickly processed and stabilised by drying. In smaller orchards, the nuts may be allowed to fall to the ground naturally, however most small and large commercial operations will use a mechanical tree shaker to maximise the volume of nuts collected in one pass of the harvester and to quickly process and dry the nuts to maximise freshness. Large orchards use Etephon, a plant growth regulator to release all the nuts from the trees at once.

    After the ripe nuts are shaken from the tree, a sweeper follows through to form windrows of the nuts. The harvester vacuums the windrow into a bin, removing some of the litter material (leaves, sticks and stones).

    The nuts are transferred to a cleaning facility for hulling, washing, grading and drying. The green husks may remain on the fallen fruit and these will be removed during hulling. Washing is required to remove dust, bird excreta and any other substances that have settled on the nuts. The nuts-in-shell are then sorted to remove immature (green) and decayed (black) ones and blank (undeveloped) nuts. The final step of post-harvest processing is to dry the nuts in preparation for sale, storage and/or further processing.  

    Drying is necessary to remove moisture from the nuts to maintain kernel quality. The nuts are dried to about 8–10% moisture content, which means they can be stored for many months without losing quality. Drying facilities will vary with the size of the operation in terms of scale and automation, however the fundamental requirements are mesh racks or bins and the capacity to generate moving air which can be carefully warmed to speed drying.

    After drying, the nuts are stored in bins until they are required to be graded for sale. The extent of grading will depend on the market that the grower is supplying. For bulk export markets, the nuts may be graded for weight, colour, size and visual appearance. Subsamples should be further tested for quality assurance and marketing information, in terms of blemishes, kernel colour and kernel yield. At this point, the nut-in-shell is ready for market. Smaller producers will grade, bag and sell nut-in-shell generally for the domestic wholesale and retail markets and farmers markets. Several producers crack their own nuts and vacuum-pack the kernels for sale.

    When processing raw product for value-adding, consideration should be given to food standards regulations, as administered by Food Standards Australia New Zealand and set out in Chapter 3 of its Food Standards Code. Information about quality assurance accreditation can be found at, but is not limited to, the websites of Freshcare and HACCP. This accreditation is becoming an increasing requirement to sell to large retailers or to export to enable traceability along the food chain.

    Some walnut growing companies purchase nut-in-shell from other growers or offer their processing and/or cracking lines under contract. A useful directory of growers and processors is provided on the website of Australian Walnut Industry Association.

  • Markets & Marketing

    Markets & Marketing

    Consumer demand is increasing for walnuts both domestically and internationally. As at 2014, the International Nut Council was reported describing international market demand for nuts as “incessant” and prices have been rising for five years despite big crops. The growth was attributed to publicity of results of nutritional studies proving the health benefits of walnuts.

    China accounts for nearly half of world walnut production (600,000 tonnes) and as at 2014, was a net importer. The United States (mainly California) produces 470,000 tonnes annually and dominates world exports. Australia produces about 12,000 tonnes annually but being a southern hemisphere producer, is able to supply the freshest walnuts on the world market for several months of the year. Most of this export volume is supplied by the large-scale producers in New South Wales and Tasmania. Chile is the other main southern hemisphere supplier. Together, Australia and Chile account for 5% of the world’s walnut production.

    Despite a premium price, Australian in-shell walnuts meet domestic demand because of superior flavour and freshness for supply as snack food, and decoration on bakery items and confectionery. The Australian Nut Industry Council reports that domestic demand for in-shell walnuts is 600–800 tonnes per year. However, due to price and a less discerning consumer, it is expected that domestic demand for walnut kernel will continue to be met by imported product.

    Market opportunities for new growers seem somewhat influenced by scale of production, i.e. producers of significant quantities of nuts have the opportunity to supply export markets; whereas smaller-scale producers target supply of in-shell nuts to local outlets, farmers markets, wholesalers and online customers.

    As at June 2014, in-shell nuts were retailing online for about $9–12/kg for large-sized walnuts and $12–14/kg for jumbo-sized walnuts. Average production at maturity for a walnut orchard can vary from 4–6 t/ha, depending on variety, inputs (particularly water) and climate.

  • Risks and Regulations Risks & Regulations

    Risks & Regulations

    Risks/challenges

    As at 2014, the prospects for the walnut industry are good, however a walnut enterprise is a long-term investment, which brings inherent risks associated with delayed positive cash flow and unforseen market changes. The trees might not come into production until the fourth to sixth year after planting, and full production is not reached until about 10–12 years after planting; and the enterprise also requires significant capital investment in machinery and processing equipment.

    There are many favourable regions for walnut production but as with most agricultural crops, a year’s production can be ruined or significantly damaged with one unseasonable weather event such as a late spring frost, a heatwave or drought. A business requires the capacity to survive a bad season.

    Cockatoos are a major problem in some regions and control measures, which are discussed in ‘Weeds, pests and diseases’ can be time and labour intensive.

    Regulatory considerations

    The regulatory considerations that apply to all Australian farms, including laws applying to chemical use and management, occupational health and safety and transport (including machinery movements and the loading/unloading of harvested product), also apply to walnut farming operations. If nuts are being processed on farm, local government should be consulted to ensure that prospective facilities and operations meet local planning and environmental regulations.

    When processing raw product for value-adding, consideration should be given to food standards regulations, as administered by Food Standards Australia New Zealand and set out in Chapter 3 of its Food Standards Code. Information about certification can be found at, but is not limited to, the websites of Freshcare and HACCP.

    If birds, especially native species, present a major problem to production and require control, growers must ensure they are fully aware of state animal protection laws and firearms laws before implementing control measures involving firearms.

     

  • Publications and Resources Publications & Resources

    Publications & Resources

    Industry snapshot - Walnuts on the website of Australian Nut Industry Council

    Walnuts fact sheet in the Nuts for Life series

    Walnuts on Austnuts website

    High Yields & Early Bearing for Walnuts & Quality Timber (2000)

    Walnut Industry Research and Best Practice Implementation RIRDC Report 04-032 (2004)

  • Industry Bodies Industry Bodies

    Industry Bodies

    Australian Walnut Industry Association promotes the walnut industry in Australia and represents growers and the walnut industry as a whole

    Australian Nut Industry Council is the national federation of seven nut producing industries 

  • Image Gallery Image Gallery

    Image Gallery

    Commercial walnut orchard (source Australian Walnut Industry Association)
    Walnut tree under commercial production (source Australian Walnut Industry Association)

    Commercial walnut orchard (source Australian Walnut Industry Association)

     

    Walnut tree under commercial production (source Australian Walnut Industry Association)

    Pruning walnut trees (source Australian Walnut Industry Association)
    Green walnuts on tree (source Australian Walnut Industry Association)

    Pruning walnut trees (source Australian Walnut Industry Association)

     

    Green walnuts on tree (source Australian Walnut Industry Association)

    Ripe walnut on tree (source Australian Walnut Industry Association)
    Whole and cracked walnuts ready for consumption (source Australian Walnut Industry Association)

    Ripe walnut on tree (source Australian Walnut Industry Association)

     

    Whole and cracked walnuts ready for consumption (source Australian Walnut Industry Association)