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18Jun

Yams find value added cropping niche

Words by Richard Rennie, images by Laney Willis

There is something highly counter-intuitive for experienced vegetable growers to want to grow a weed. But for Warren and Michelle Jones, that is all part of what makes their choice of commercial crop special, and unique amidst Canterbury’s many cropping opportunities.

The couple are into their fourth full time season growing yams, made so distinctive with their knobbly appearance and attractive red or yellow hues.

For a certain generation of consumers, yams will bring back vivid memories of Sunday roasts, with yams’ sweet taste contrasting to the usual potato, kumara and pumpkin mix that made up the roasted vegie platter.

Few may appreciate it, but strictly speaking the tuber is a weed, part of the oxalis family oxalis tuberosa, distinguished by their tuber root system, and so often the headache of home gardeners when trying to remove them from flowerbeds.

“It does seem strange as a grower to be planting something that is related to a weed, and in some respects you do have to treat it like a weed. In others you treat it very much like the commercial crop it is,” says Warren.

Anywhere else in the world the yam is known as the “oca” while somewhat confusingly for Kiwis, the kumara is called a yam overseas.

The plant’s DNA steps back to the Peruvian Andes, where a variety of colours and lengths are grown on latitudes shared by Warrens’ Rakaia district.

There are extensive efforts overseas to collect varieties of yams from South American countries to ensure their diversity and viability are maintained, given their historic significance.

Here in Canterbury Warren and Michelle are putting a commercial spin on those preservation efforts, quietly overseeing a resurgence of yams back onto the dinner menus of a new generation of Kiwi diners, and also creating a value-added niche on Canterbury’s market gardening map.

“Between my teens and my 30s I don’t think I would have seen a yam, and earlier on it was often because they may have been growing in your parents’ garden, but they did seem to vanish for a while,” says Warren.

Today there are four main growers in New Zealand, two in the South Island and two in the North. The Joneses are also taking growing to the next stage with their pre-packed Murphy Pack brand of yams, distributed through Progressive and Foodstuffs supermarkets nationally.

But it has not been a straight leap into the quirky vegetable’s market, and for Warren is the culmination of a lifetime spent in the market gardening- vegetable growing industry from when he left school at 16.

“My goal was always to have my own growing operation that was large enough for us to both work in it fulltime.”

Warren started his career working for a seed potato grower in Highbank after leaving school and eventually they did purchase a small growing property which they ran for 6 years before selling.

The couple saw the yam business on the market fifteen years ago but it was unable to support them fulltime, leaving them to work on the Murphy Pack project over weekends and after hours while Warren continued to work fulltime in packhouse operations in Canterbury and Michelle at the local BNZ.

“Then we got talking to the people at MG Marketing (produce distribution company) who suggested we should commit totally to the operation.”

“They helped us out a lot with the promotion, branding and marketing side of things, and helped give us confidence to really push the business forward.”

The couple grow the yams on 23ha of leased land, moving to a new patch every year in a year-long planting-harvesting cycle that is aligned with the equinox for planting in October, harvesting from May-September.

“This fits well for a lot of farmers, for this period of time it is a good break crop. You sometimes initially have a little hesitancy from those that think of it as a weed, but the residual is easily cleared out and well gone after a year.”

While similar to a weed in that they are best left to grow in the early stages of planting in October, yams can be a temperamental crop demanding more attention as the tubers begin to fill out.

Yams require a long growing season with lower evening temperatures early on in planting, and longer daylight with high temperatures later on in the growing stage, making Canterbury an ideal environment for them. Ample supplies of water are also needed to ensure they reach their full size.

“They do not like stress, and they need quite a bit of water as they start to fill out, up to 25mm an application. But this usually works well because it comes after the demand has passed from other crops. A lack of water or an early frost can be the two main stresses for them.”

Warren finds the yams a rewarding crop to plant and harvest, with a relatively low environmental footprint attached.

“As a crop they don’t receive any nitrogen, which is a good thing when dealing with nutrient loss issues, but they do need potash. Our main pest is grass grub, and if it wasn’t for having to control that, they would be virtually an organic crop.”

The crop is well suited to the rich, well drained Waimakariri silt loam soils around the Rakaia district, returning a healthy yield per hectare.


Harvesting is drawn out between May and September, again adding to the crop’s appeal for its ability to fit around the usually earlier seasonal demands of most other crops. The tubers are not time-critical for harvest, meaning wet weather can be worked around relatively easily without crop spoilage.

“Crop yields are pretty comparable to onions or potatoes. Last season we managed 11t a hectare, up from 8t the year before.”

Harvesting is done using an adapted potato harvester which is adept at plucking the tubers off the attached foliage after the frosts come with adaptations to the web belts and sieves ensuring the relatively tender yams are not damaged in the process.

The couple have recently commissioned a new packhouse/processing facility that this season will include a newly imported Danish pre-pack line that brings the grading and processing firmly in-house for the first time.

“Yams do tend to be quite labour intensive at this point due to their shape and size, and here in New Zealand we tend to grow relatively small yams, which can take more time to process.”

Calling on a loyal corps of locals to help over the harvest season, they also boost the numbers with backpackers and despite the challenges of Covid travel bans, have managed to find some keen workers for this season.

“Overall last year we were quite lucky in that the yams were in the ground when lockdown came on, and harvest came after lockdown was lifted, and there were still quite a few people around looking for work.”

They had been concerned about how consumers would respond over the pandemic period, but have been pleasantly surprised to find demand is sound, and if anything growing for the interesting tuber.

As a food item, yams are dense with carbohydrates, even more so than potatoes and their appeal is enhanced by a sweet taste profile.

The couple keep back selected quantities each year as a source of seed stock, with colour varieties extending from a beet like purple, to red and yellow.

This season they have their own “red eye” special breed being packed for their first time- a yellow yam with a distinctive red eye, with a distinctive lemony taste and something that has taken the couple three years to cultivate in volumes sufficient to sell commercially.

Warren says the big supermarket chains have been very supportive of the Murphy Pack brand, encouraged by the results they are witnessing with potatoes being removed from their generic 10kg sacks and into convenient pre-washed pre-sized boxes with cooking suggestions.

“Often people are not sure what to do with them, but there are options other than just roasting. They can be sliced up thinly to go into salads raw, and even the leaves are very edible.”

Warren says they have considered other options for processing, including yam chips, as a new generation start to explore yams as a new food option.

With their twins aged 13 and a 16-year old, life like the business is busy for the couple. Warren says they are keen to see how the next two years go with the new pre-pack line in place, and possibly a new harvester to speed things up in the field. 

They also want to focus upon keeping their seed stock up to meet demand, in a crop that is proving to be popular with consumers, and the rejects very popular with assorted livestock herds around Canterbury.

Warren is optimistic their interesting crop has an assured future among the rotations on the Plains, but he remains concerned over the ever-increasing pressure on growers, whether in terms of quality land supply, or environmental regulations.

“I think it is tending to be forgotten that we all need to eat, and we need land to provide for that. But the challenges around water and compliance are pressing from one side, while the demand for good land for housing is coming from the other side.

“It affects everybody, and I am not sure that everybody is really thinking about it like that however.”

Warming yam soup recipe

While many people will be familiar with yams in the Sunday roast, Michelle Jones has a warming appetising yam soup that makes a change from the usual winter soup line up and is easy to make.

Chop up one onion, or a leek, and a couple of celery stalks, and cook until soft then fill the pot up with yams and add vegetable stock until nearly full.

Season the pot with salt and pepper and Masterfoods Thai Seasoning – this may require quite a bit of seasoning to bring up to full flavour.

Bring the pot to the boil and simmer until the yams are soft and mushy.

Depending upon your preference for a smooth soup, you can either eat the soup as it is, or put it through a food processor and then reheat if necessary.

Another variation to sweeten the soup is to roast the yams first which makes the skins go silky.

Be sure not to forget to add the onion or the leek if you cook it this way, otherwise the soup will be quite sweet.

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