Image caption Blake Anderson shows off the wasabi plants in one of his three greenhouses on Vancouver Island in Canada

For nearly 30 years, Brian Oates has, in his words, "pig-headedly" devoted himself to a single pursuit: setting up the first commercial wasabi farm in North America.

Dozens of others in the US and Canada have tried to grow the plant - a type of horseradish that originates in Japan, where it is found growing naturally in rocky river beds - but almost all have failed.

The reason is simple: wasabi is deemed by most experts to be the most difficult plant in the world to grow commercially.

So what drives Mr Oates, and his business Pacific Coast Wasabi (PCW), other than his stated stubbornness?

The price.

Image caption At market rates, a kilogram of wasabi goes for around $160, making it one of the world's most lucrative crops

Fetching nearly $160 (£98) per kilogram at wholesale, in addition to being hard to nurture, wasabi is also one of the most lucrative plants on the planet.

"It is much like gold - we expect to pay a lot for gold. Well, we expect to pay a lot for wasabi," says Mr Oates.

The real thing

The first thing to know about wasabi - or Wasabia japonica, as it's officially known - is that you have probably never tried the real thing.

That light green paste nestled next to the pink ginger in your box of sushi? It is most likely a mix of mustard, European horseradish, and food colouring.

In fact, by some estimates, only 5% of the wasabi served in Japanese restaurants around the world comes from the rhizome, or root, of a wasabi plant.

How to eat wasabi

Image copyright Thinkstock

The methods for eating real wasabi differ significantly from those of the powdered kind, particularly if the plant is fresh.

In its most traditional preparation, the root is stood on a grater made of a piece of sharkskin stapled to a wooden paddle. Using a circular, clockwise motion, one presses the rhizome down and a paste is formed.

The heat and flavour - significantly less bracing than imitation wasabi, but similarly sharp - last only for 10 to 15 minutes, so wasabi is grated as needed.

Nobu Ochi has been buying the wasabi Mr Oates produces from the beginning, and selling it to customers at his Zen Japanese restaurant in downtown Vancouver.

"We send the grater out with the wasabi in it, and let them have the experience of grating fresh wasabi," says Mr Oichi.

"Once they taste it, like anything else that's good, you don't want to go back to the other stuff."

Wasabi was initially used by the Japanese many centuries ago as a way of preventing illness: the story goes that it was used on raw fish to prevent food poisoning, not because of its spicy taste.

But because wasabi is grown in a manner unlike most other crops, it has long been mostly cultivated by the Japanese for the Japanese market.

"It's a water loving plant, but it does not grow completely submerged in water like a water lily or something," explains Prof Carol Miles, from the Department of Horticulture at Washington State University .

"In general, water flows over the crop, so it's grown in water beds and that's not something we commonly do in North America."

Hatching a seed

In addition to wasabi's unique cultivation, the problem for the would-be North American wasabi farmer has also been access - getting their hands on seeds or cuttings from which they can try to grow the plant.

Image caption Wasabi can be grown from both seeds or cuttings from a so-called "mother" plant

"Access to the plant material has really been the bottleneck," says Prof Miles.

Mr Oates says he first became interested in farming wasabi in 1987, but it took him six years simply to get access to viable seeds from which he could grow the plant.

For years, he grew the crop in greenhouses on the University of British Columbia's (UBC's) campus in Vancouver, where he worked at the time, but kept running into problems.

Finicky wasabi, if exposed to too much humidity, would die; the wrong nutrient composition could lead to a similar fate.

And then, there was the problem of scale.

"There seems to be an understanding in agriculture that when you keep your crop small it's fine, but then when it gets big all of these issues you didn't have before rear their ugly faces," says Mr Oates.

He notes in particular that wasabi is especially prone to disease when planted on a large scale.

But finally, after working with graduate students at UBC, he developed a method - which is now a trade secret - that allows wasabi to be cultivated on an industrial scale without succumbing to disease.

Money woes

Mr Oates then encountered an issue common to almost every start-up, from a farm to a technology business - where to find financing.

Image caption Brian Oates has pursued his dream of running a commercial wasabi operation since the 1980s

"There was no-one willing to take a risk on something as unknown as wasabi," he says.

That forced him to embrace the model currently employed by PCW, which is essentially that of a franchise.

PCW's first commercial farm opened on Vancouver Island in 2012, and it currently has nine in total - four in British Columbia, four in Washington State, and one in New York.

The farmers have each spent $70,000 to get a licence from Mr Oates, letting them in on the secret method to grow wasabi in greenhouses.

On average, each farm has then spent $700,000 per acre of wasabi just to get up and running.

Adding the fact that wasabi takes just over a year to mature means that the farmers have to be patient before the profits start to roll in.

'The window's open'

Blake Anderson and his wife, Jane, operate a successful PCW farm on Canada's Vancouver Island.

Image caption Each acre of a wasabi farm costs approximately $700,000 to get up and running

In three greenhouses situated atop a hill, Mr Anderson has what many have long thought was impossible: a successful, commercially viable wasabi farm.

"This one was so big that I needed to get a shovel to get it out of the ground," says Mr Anderson as he proudly holds up a gigantic wasabi root.

"You'll need a football team to get the next harvest," jokes Mr Oates, who has come to pick up some of Mr Anderson's crop, so that it can be shipped to a network of suppliers, and then onto restaurants that will buy the wasabi for a price of up to $308 per kg.

A former truck driver, Mr Anderson says he was attracted by the challenge of wasabi.

Image caption Mr Anderson has three wasabi greenhouses on his property, built over the course of two years

Now, two years in, he says: "We've learned an awful lot, but we're getting pretty good at it." His 200g wasabi rhizomes are a testament to his success.

Whereas PCW previously had trouble keeping up with demand - leading to sporadic halts in orders as the company waited for crops to mature - Mr Oates now says he thinks the business can increase the total acres of wasabi it grows from 10 currently to 20 to 30 in the next few years.

Image caption The wasabi greenhouses are located in an idyllic part of Vancouver Island, a two-hour ferry ride away

"We're in a different era now, where we can make this happen and we're not worried about shutting down," says Mr Oates.

"The opportunity's there, the window's open and it's our job to make it happen."

Potential health benefits

Now that the culinary side of the business has legs, Mr Oates and his colleague, Albert Agro, have hopes of expanding into pharmaceutical products.

Mr Agro, who is chief executive and president of Wasabia, the medical side of the business, says studies have shown that extracts of wasabi can have health benefits, such as anti-bacterial and stomach-calming properties, and the ability to help reduce wrinkles.

The difficulty, as with most plant-based medicines, is to produce enough wasabi consistently to be able to generate a product. There are efforts under way in New Zealand and China, and there are already some wasabi supplements available on the web.

Wasabia has plans to begin medical trials later this year in Malaysia, but Mr Agro says that the company is focused on the longer term, content to wait until there is enough data to back up a pharmaceutical product.