Les Baguley's calloused hands scratch at the soil his family has tilled south-east of Melbourne for 120 years over four generations.

From the tangle of purplish-green leaves and matted roots he plucks another giant tuber, shaped like a huge purple molar.

"It's incredible. I think we've dug 300 kilos off a 40-metre bed," enthuses the veteran market gardener.

Kneeling in the dirt alongside him, Dr Chris Williams, a horticulturalist from the Burnley Campus of Melbourne University, shares his excitement.

Dr Williams runs a program called Novel Crops, a quest to see what unusual vegetables and food plants can be grown successfully by backyard gardeners in temperate Melbourne.

This trial at Mr Baguley's commercial market garden in Clayton South is already being declared a great success.

Most thought sweet potatoes could never be successfully grown in Melbourne's cool climate.

"The really important thing is that they just need that five- or six-month growing season," Dr Williams said.

"And so Melbourne now, with the urban heat island effect and climate change, seems to have the right climatic conditions to grow a very good sweet potato crop."

Of half a dozen varieties in the trial, two are giving outstanding yields — the Beauregard, an orange variety commonly seen at the greengrocers and Northern Star, a purple-skinned, white fleshed variety.

The trial is no mere novelty. Also keenly watching is FareShare, Australia's largest supplier of meals for charity.

FareShare's kitchen in inner Melbourne, staffed mostly by volunteers, runs around the clock, daily turning out up to 5,000 meals to the needy.

The Beauregard, an orange variety of sweet potato commonly seen at the greengrocers and Northern Star, a purple-skinned, white fleshed variety. ( Landline: Tim Lee )

Until now, the charity has relied on food donated by supermarkets, produce stores and growers.

A year ago it began to use community gardens, also staffed by volunteers, to supplement its menu.

At the top of the request list, especially from migrant groups it sends meals to, were sweet potatoes.

Many, from tropical countries, missed the taste of this ancient vegetable.

Scientists believe it was domesticated in Central America at least 5,000 years ago, making it one of the oldest and most important vegetables known to humankind.

But over time in the Western world, the common potato gained precedence.

Dr Williams is thrilled to see the vegetable's recent resurgence in Western diets.

"People have started to see them as a more mainstream crop, but also aware the that coloured ones, the orange and the purple ones have these pigments, like the anthocyanins," he said.

"People have become very aware of them as an antioxidant so they have become to be associated with the 'superfood' concept."

FareShare cooks up to 5,000 meals for charity every day. ( Landline: Tim Lee )

In less than a year, FareShare's community gardens, dotted around Melbourne's outer suburbs, have contributed more than 20 tonnes of vegetables — about one third of FareShare's vegetable requirements.

Sweet potatoes have some practical advantages also — a longer shelf life than most fruit and vegetables and they form a key part in Asian dishes such as curries and stews.

FareShare chef Kelly Watson has thoroughly evaluated the sweet potato trial for yield and usefulness and she is excited.

"Over the last couple of years we've found it very hard to secure enough vegetables to make sure each meal was having adequate nutrition and with the advent of our vegetable gardens coming on, a year on we've found that they're supplying 30 per cent of all of our vegetable requirements, which is just fantastic," she said.

There is another unexpected spin-off.

At FareShare's community garden, a flourishing plot that used to be a rail-yard dumping ground at Abbotsford, a team of keen volunteers is plucking the autumn harvest of sweet potatoes from the soil.

English language students practise their language skills with Dr Williams. ( Landline: Tim Lee )

They are English language students, a wide range of nationalities, for whom sweet potatoes are a familiar dietary staple.

They are learning and practising their language skills as they work.

For Tesfay Hayle, who arrived in Australia a year ago, the community garden has been a godsend.

He fled strife-torn Eritrea where civil war left him orphaned.

"When I come to Australia I feel lonely," he says softly.

"But if I work together it's good for me."

For Mr Baguley, whose generous heart is as broad as his smile, the successful sweet potato trial will only get bigger.

He already has five charities, including FareShare, utilising his precious soil.

"I do it because I enjoy helping people and teaching students how to grow this stuff," he beams.

"I think it's about educating people that you can grow different crops in Victoria.

"Just because we're a temperate climate doesn't mean you can't have a go."

Tim Lee's story Sweet Dreams screens on Landline at noon.