When it comes to growing crops, Elwyn Powell, of Wanganui, will give just about anything a go.

Over the past two decades, the regional branch chairman of Federated Farmers has combined agricultural contracting with growing wasabi, radishes and squash for the Japanese seed market, as well as the usual grain crops.

So the opportunity to legally grow a crop from the cannabis species was just too good to miss. Of the hundreds of varieties of cannabis, only some contain a lot of THC, the active compound that provides a high.

The many varieties that have a THC content of less than 1 per cent are grown as hemp all over the world for fibre and hemp-seed oil.

Mr Powell is one of a handful of people in the country who have been granted a licence to grow the plant as part of a national trial.

Prospective licensees were vetted to ensure they were reputable citizens with no convictions for drugs or other crimes - and even then they had to wait because the seeds, imported from Canada, were impounded in the United States, and did not arrive until November.

Mr Powell planned to plant two 2ha blocks - one to be used for sustainable seed production and the other to be harvested for silage, which would then be tested as to its suitability as a stock food. But the early experience of some other growers showed that only 50 to 60 per cent of seeds were germinating.

So he reduced the area to 3ha - a decision he has some regrets about because his crop is thriving.

"All I've done is put it in the ground and left it. Compared with other crops, hemp is a breeze."

A few rabbits had been a problem, and he had been careful to select paddocks that were clear of possum habitat.

"I've been told it makes pretty good dairy feed. I'll give the cows a high while the farmers are on holiday," he quipped.

"Seriously, there is little likelihood of anyone getting a buzz from hemp. "If it's over 0.3 per cent [THC] we've got to kill it. Marijuana is 9 per cent THC."

Seed oil has a distinctive nutty flavour and is ideal for use in salads, dips and marinades.

The seed, which is about the size and shape of a peppercorn, is more nutritious than soyabean and contains more fatty acid than any other source.

It is second only to soyabeans in complete protein (but is more digestible by humans), is high in B vitamins and is 35 per cent dietary fibre. The seed contains no THC.

Mr Powell sees huge potential in the plant.

"As a crop, it's environmentally sustainable. No pesticides or herbicides are required and there are so many uses for it."

Hemp fibre was longer, stronger and more absorbent than cotton.

"It really is a wonderful plant. If we can get it established, it's got so much potential.

"We've just got to find the right one for us and what its strengths are under our environmental conditions."