(Stuff) - A Marlborough marine farmer is turning his trash into another man's treasure by producing a plant feed for vineyards using seaweed.

Mick Norton initially panicked in the late 1980s when the mussel lines he developed in Tory Channel, in the Marlborough Sounds, started attracting large amounts of kelp growth.

"My wife Mary and I tried cutting [the kelp] off, but it kept growing back, and then we finally thought, maybe there's a market for this stuff," Norton said.

A natural soil conditioner, kelp encouraged earthworms and good health to both soil and the plants that grew in it, he said.

Norton was particularly interested in finding a use for the kelp within Marlborough's young and developing grape industry.

After years of work, he developed two such products, a foliar spray, Natural Kelp Tea, and a kelp pulp product, Pure Farmed Chopped Kelp.

"Historically kelp has been used by many countries in the world, kelp and seaweed properties have enhanced gardens for hundreds, if not thousands of years," he said.

Norton's venture started small, using 100-litre barrels to ferment the kelp, working on the process until he perfected the foliar spray.

His research took him on a trip to Hokkaido in Japan in 1991 after discussion with the Department of Scientific and Industrial Research, now known as the Crown Research Institute, and in 2013 his marine farm at Hitaua Bay was Certified Organic for Seaweeds by AsureQuality.

Last year, he began producing the spray in 2000-litre and 3000-litre stainless steel tanks.

"Our breakthrough really was when we started fermenting in 1000-litre pods in the Sounds, naturally breaking down the system.

"Slowly we developed a method to consistently make a kelp tea, and also a kelp pulp product which was used for agriculture and orchard practices."

A handful of businesses including Cloudy Bay Vineyards, Seresin Estate, Lake Chalice Wines, Huia Vineyards and Lovelock Vineyard, started using Norton's kelp products, and have continued to do so.

Norton believed what set his products apart was the 100 per cent natural, cold, wet process he used to make the spray, allowing the kelp to retain its natural goodness.

"Scientists believe that 15 per cent of the goodness is lost [from seaweed] just by drying it," he said.

"Stainless steel tanks allowed us to make our fermenting system much more effective and increase our quantity dramatically, while retaining the quality … they produce a liquid that uses 99.9 per cent of the seaweed product and leaves virtually no residue in the tank.