Manuka – Honey and Oil
Mānuka or kāhikatoa (Leptospermum scoparium), called ‘tea tree’ by Captain Cook, is a rather variable plant ranging from flat creeping forms and small shrubs to tall trees (up to 7 m). Mānuka/kāhikatoa is common throughout the North, South and Stewart Islands, in lowland to low alpine regions up to 1800 m above sea level. It can be found in many different habitats including wetlands, river gravels and dry hillsides. When mature, it is very tolerant of drought, waterlogging, strong winds and frost, and it can grow at less fertile, colder, wetter and more acidic sites than kānuka.
For more than a century, mānuka has been an obstacle for New Zealand farmers, with thousands of hectares of mānuka cleared to make way for farmland. However, recent discoveries have changed the landscape, with many hectares of mānuka now being planted again.
The main driver for the interest in mānuka has been the finding that mānuka honey has important anti-bacterial properties that makes it different from other honey.
In 2008, it was discovered that the cause of much of this difference was a compound called methylglyoxal (MGO). A year later, scientists at the University of Waikato (Christopher Adams, Merilyn Manley-Harris and Peter Molan) published research showing that the methylglyoxal in New Zealand mānuka honey originates from the chemical compound dihydroxyacetone (DHA), which is present in the nectar of mānuka flowers to varying degrees.  (Some mānuka plants have more DHA in their nectar than others.)
DHA does not have antibacterial properties, but over time DHA converts to MGO through a natural chemical reaction. DHA is unique to mānuka nectar, and has not been found in any other floral types of honey. Moreover, storage of these honeys at 37° Celsius led to a decrease in the DHA content and a related increase in MGO. In other words, if the nectar has a high DHA level, then the resulting honey will have a high UMF rating.
Unique Mānuka Factor (UMF)
UMF stands for Unique Mānuka Factor, and is a quality trademark and grading system identifying natural unadulterated mānuka honey that has a special unique natural property found only in some strains of mānuka honey.
These anti-bacterial properties are unique to New Zealand mānuka honey, hence the name ‘unique mānuka factor’, and have been responsible for the production of high-value medical-grade honey products that assist in treating wounds, as well a range of bio-medical products to address a variety of skin conditions. Also, research is starting to show that medical-grade mānuka honey may be able to help in the fight against antibiotic-resistant infections by improving the effectiveness of the anti-biotics.
Below is a table comparing the UMF rating with the minimum rating of Methylglyoxal (MGO) required.
In terms of the value that mānuka honey UMF factor contributes to total New Zealand honey exports, the table below shows the 10 biggest exporters of honey (all types) in the world by value as at 2013. New Zealand is at number three, with a per tonne price around three or more times the price of other countries. This premium pricing is due, to a large extent, to the value of high UMF honey.
Overseas producers were quick to recognise the premium associated with mānuka honey, and unscrupulous operators rebranded their honey as mānuka honey to achieve better profits. Due to this product piracy, the Ministry of Primary Industries is developing a testing regime with the industry to distinguish legitimate mānuka honey from pirated product.
There are many options available for landowners to be involved with mānuka production, from minimal involvement – providing the land for the mānuka to be planted on and contracting a company to look after the rest of the process, through to high involvement – setting up a business growing mānuka, collecting honey and/or oil and marketing the product through distribution channels. Returns are higher for the latter, as is the level of skill, experience, knowledge and resources required.
The recent discovery of myrtle rust in New Zealand and its potential danger to mānuka and other plants has raised questions about the future of the industry, and will necessitate intensive research into the likely impact this will have on the mānuka honey and oil industry.
Myrtle rust is a serious fungal disease that affects plants in the myrtle family, which includes pōhutukawa and mānuka. In early May 2017, the disease was first detected on mainland New Zealand in plants at a nursery in Northland. It has since spread to Taranaki, the Waikato and the Bay of Plenty.
MPI and other partner government agencies have short- and long-term strategies to combat myrtle rust. The immediate aim is to eradicate the pathogen at source, and if that is not possible, the long-term strategy is containment, monitoring and learning to manage myrtle rust. More information on Myrtle Rust can be found at http://mpi.govt.nz/protection-and-response/responding/alerts/myrtle-rust.
 Mānuka/kahikatoa and kanuka, Dept of Conservation
 DHA and MG explained, Analytica Laboratories
Mānuka honey and mānuka oil are the two main products from mānuka. Retail prices for mānuka honey attract a premium, especially those with a high UMF rating. Top of the range UMF20+ mānuka honey retails for $260.00 for 250 g, i.e. $1040 per kg.
One hundred percent pure mānuka oil retails for $600–3,000 per litre.
The global honey market is growing, and in 2013 was worth over US$2 billion, with the top ten importers growing by over 50 percent in the five years from 2009–2013, from $946 million to $1.5 billion.
New Zealand honey is exported to 48 countries around the world. In 2016, 6924 tonnes were exported at a FOB value of NZ$258 million, giving a price per tonne of NZ$37,271. Mānuka honey figures are not separated out in Statistics NZ figures, although it was estimated that 1700 tonnes of mānuka honey were produced in 2016.
 ‘Riddle of how 1,700 tons of mānuka honey are made… but 10,000 are sold’, NZ Herald, 23 Aug 2016
Successful mānuka plantations rely on a number of variables, including careful planning and plant husbandry, good relationships between landowners, beekeepers, mānuka nurseries and honey/oil marketing companies and, for honey, an understanding of bee behaviour.
Cultivar selection is highly important in establishing a successful mānuka plantation. Mānuka cultivars need to be chosen for the specific geographic areas where they are likely to flourish. All mānuka will not necessarily grow anywhere. However, if possible, planting several cultivars can extend the flowering period from 6 to 12 weeks. Mānuka nurseries will be able to provide advice on this.
Ideally, mānuka cultivars should be able to produce high UMF, i.e. high DHA level in their nectar, as well as good growth rates, high disease resistance and good flowering ability. Work developing new mānuka cultivars is ongoing.
Natural mānuka lifespan is 25–50 years, although the mānuka productive lifespan is based on 25 years.
When planting for honey, mānuka can be planted on marginal and hilly land, which may help improve the productivity of more marginal land, at a stocking rate of approximately 1100 stems per hectare or at 3 x 3 m spacing. When planting for oil, ideally land would be flatter and the stocking rate could be increased to maximise productivity, to as high as 30,000 stems per hectare or more. For the first three years of the crop, areas may need to be fenced and protected from predators that will eat or damage younger mānuka plants, including hares, goats and deer.
Unfortunately, bees prefer other floral crops to manuka, and therefore, if given other food source options, will likely avoid mānuka. Therefore mānuka plantation layout becomes important, and should be undertaken with beekeepers so as to limit bee choices. Current industry wisdom is to plant mānuka for honey in large contiguous blocks of 20–30 hectares or more, and the plantation should be laid out so that hives can be positioned towards the centre of the blocks to provide fewer food source options for the bees.
Hives should still be sited according to apiculture industry norms, i.e. in sunny, sheltered positions with good access for vehicles.
The first honey harvest begins in year three, with maximum honey yields occurring from year eight onwards. For plantation models of mānuka honey where there is more control over the environment and inputs, yield may be able to be brought forward, with a 20–30 percent harvest by the end of year one, and maximum honey production achieved by the end of year three.
Hive stocking rates can range from approximately one hive per hectare for indigenous manuka, through to plantation stocking rates of four or more hives per hectare. Yield varies according to a number of factors, including climatic conditions, dilution from other nectar-producing plants, and bee health; however, a yield of 25–40kg/hive is considered reasonable.
Once the honey has been harvested, MGO levels increase over a 12–18-month period. Most beekeepers store their honey until the MGO levels reach their peak.
There are two general approaches to harvesting mānuka for oil – planting and harvesting manuka on flatter land or harvesting existing manuka which is usually on hillier land. If the mānuka is to be planted, flatter land is preferable, as this allows the foliage to be harvested by machine, which is more efficient. This also influences the layout, for example, planting in hedgerows, which allows a higher number of trees per hectare, anything from 5,000 – 30,000 trees per hectare or more. Irrigation should also be installed to promote faster growth. Approximately one tonne of mānuka foliage can produce between two and three litres of pure mānuka oil. The harvesting rotation may vary according to how heavily the mānuka is pruned or cut back, from twice-yearly for lightly-trimmed to every second or third year for heavily cut back mānuka. Pruning promotes new growth and encourages the tree to bush rather than turn into a tree with a canopy.
Mānuka growing on hillier ground can also be harvested for oil, but will likely require manual harvesting which decreases efficiency and may provide more variable results.
Distillation of mānuka oil
Mānuka oil can be extracted from the foliage by steam distillation or carbon dioxide (CO2) super-critical extraction.
In the steam distillation process, steam is passed through the foliage and when condensed it contains a small quantity of pure mānuka oil. This oil floats on top of the condensed water and is drawn off.
In the CO2 extraction process, which requires less heat, carbon dioxide is pumped under pressure into a chamber filled with plant matter. When carbon dioxide is subjected to pressure it becomes ‘supercritical’, i.e. has liquid properties while remaining in a gaseous state. Because of the liquid properties of the gas, the CO2 functions as a solvent, pulling the oils and other substances such as pigment and resin from the plant matter. In some cases, CO2 extraction can provide a superior product.
Oil distillers must have the knowledge and expertise to know how to produce therapeutic-grade essential oils.
The infrastructure required varies according to whether planting for honey or planting for oil.
When planting for honey, mānuka can be planted on more marginal and hilly land so minimal infrastructure is required, although areas may need to be fenced to protect from predators.
Planting for oil will require more infrastructure, including machine harvesters to increase efficiencies, and facilities for extracting and packaging oil, including distillation units.
Mānuka does well in a range of soil types: sand, volcanic, clay, peat, limestone, alpine and pakihi; swampy soils where the roots of the plant never dry out.
- It can be planted on barren windswept hillsides where it may be constantly battered by salt-laden winds.
- A good site is a sheltered valley with high hills on either side.
- Mānuka thrives on north- and east-facing hillsides.
- Avoid proximity to large sources of non-mānuka nectar.
No research is available for nitrogen leaching of mānuka, however it is considered to be in the low range.
The High Performance Mānuka Plantations PGP 2017 review , has confirmed some questions around the development of mānuka plantations to assist with future growth.
- Soil type affects plant growth, flowering time and duration, flower numbers and nectar yield but not nectar quality.
- Different cultivars respond differently on different soils.
- Contrary to the previously reported studies, mānuka has better growth and produces more flowers on soils with more nutrients.
- Light experiments mimicking NZ’s latitude range did not affect plant growth, flowering time or nectar quality.
- Cultivars have differing drought tolerance.
- Water deficit did not alter DHA levels.
- Temperature doesn’t seem to affect levels of higher or lower quality nectar, but temperature has a significant influence on nectar (and honey) production.
- Bees seem to prefer cultivars with higher sugar content in the nectar.
- The data has shown that despite some variations, the Comvita seedlings are generally yielding higher DHA concentrations than wild mānuka.
- Glasshouse and field trials have generally given similar results, so cultivar proving may be able to be carried out in the nursery in the future.
- Some trial cultivars have consistently over four seasons produced nectar with two-times the level of DHA compared with wild local mānuka.
Genetics are the main driver of mānuka nectar quality and it also influences flowering period and flower numbers.
Mānuka is particularly susceptible to invasion by scale insects and consequent sooty mould growth.
Areas of planted mānuka may need to be fenced for the first three years of the crop to protect from predators, including hares, goats and deer, that will eat or damage younger mānuka plants.
 https://tararuacropping.files.wordpress.com/2016/08/essential-oil-manuka-may-2014_kanuka.pdf, Crop and Food Research, July 2000, Accessed June 2017
Mānuka honey income is affected by a number of factors, including the climatic conditions of the season affecting nectar flow and bee activity, the DHA levels of the nectar, the species, area and density of the mānuka and the presence of other floral food sources.
The cost per hectare to plant mānuka can vary widely according to the stocking rate and quality and size of plants, etc. Initial estimates for planting on marginal land range from $2000–3000 per hectare including plants and labour.
Fencing costs can average $15 per metre on flat land.
For plantation mānuka, high intensity stocking rates when planting for manuka for oil can increase planting costs significantly. If seedling costs are $0.70 each, a stocking rate of 30,000 plants per hectare will produce a plant cost of $21,000 per hectare. There would also be additional infrastructure such as weed matting and irrigation.
Returns for honey to the landowner can vary considerably from year to year. For mānuka honey, there is insufficient past data to provide a demonstrable rate of return, however estimates by Comvita and Kauri Park provide for a return of between $500 and $1360 per hectare to a landowner.
Returns from mānuka oil can vary according to the ecotype of mānuka harvested, the ease of harvesting the mānuka foliage and the type of extraction method used, which all flows through to the quality of the oil produced. One tonne of foliage can produce two to three litres of pure mānuka oil with a retail value of $600–3000 per litre.
Mānuka plantations are eligible for funding under the Afforestation Grant Scheme (AGS). The AGS provides $1300 per hectare to successful applicants towards the establishment of trees on their land, in return for the first ten years’ worth of carbon credits. The 2018 funding round will open in the first quarter of 2018.
 High Performance Manuka Plantations presentation, John Burke, Comvita, 2015
 Mānuka Genetics presentation, Andrew Wearmouth, Kauri Park, August 2016
Mānuka Farming NZ
The Mānuka and Kānuka Plantation Guide, Boffa Miskell Ltd, April 2017 (https://landusenz.org.nz/wp-content/uploads/2017/08/The_Manuka_and_Kanuka_Plantation_Guide_May_2017)
Planting Mānuka For Honey Production, John Burke, Comvita (https://www.youtube.com/watch?v=qLzThyxbgKo)
Preparation for a Mānuka Plantation in 2016, Kauri Park Nurseries (http://www.kauriparknurseries.co.nz/preparation-manuka-plantation-2016/)
Developing Mānuka Plantations, Crete Wana, Mānuka Bioactives Ltd (http://www.rotorualakes.co.nz/vdb/document/1173)
Mānuka Establishment Basics, PF Olsen and Mānuka Farming NZ (https://nz.pfolsen.com/market-info-news/wood-matters/2016/april/manuka-establishment-basics/)
High Performance Mānuka Plantations presentation, John Burke, Comvita, 2015 (http://www.rotorualakes.co.nz/vdb/document/1174)
Mānuka Genetics presentation, Andrew Wearmouth, Kauri Park, August 2016 (http://www.kauriparknurseries.co.nz/wp-content/uploads/2016/08/Manuka-Genetics-Andrew-Wearmouth.pdf)