The world’s most expensive vegetable — the Japanese wasabi — has been successfully grown in Ireland for the first time.

The sushi accompaniment, traditionally grown in mountain streams of its native habitat in the Japanese Shizuoka Prefecture, is worth a cool €1.5m an acre.

But RTÉ’s farming series Ear to the Ground reveals how the plant, which is notoriously difficult to cultivate, has been carefully nurtured in a garden just outside Tandragee in Co Armagh.

Chemist Sean Kitson and his son Zak have made a little bit of history as one of the world’s most expensive crops has just finished its two-year growth cycle.

“It’s green gold,” said the scientist after successfully growing a shaded polytunnel full of wasabi worth around €45,000.

“It’s very difficult to grow,” said Mr Kitson. “You can have problems with root rot, the optimum temperature is 12 degrees but in summer when it gets hot it can get up to 40 to 50 degrees in the (polytunnel) so that slows the growth down. The light will burn the plant, so we have to reduce it by 80%.”

Wasabi is best known as the green paste which accompanies sushi but many of the pastes are concoctions of horseradish, mustard, sugar and green colouring as the plant is so tricky to grow.

The fresh wasabi root grown in Ireland is put to the taste test on the programme at the Zen restaurant in Belfast run by Eddie Fung, who said he had never been able to source it from Ireland.

On tasting the plant, he called it “fantastic”.

“It is seven or 10 times stronger. People will love it. Especially if we can grate it in front of the customer.”

Mr Kitson originally decided to grow the plant because of it reputed anti-inflammatory properties as Zak was diagnosed with multiple sclerosis as a child.