How green is my Aire Valley... and it's still only early spring

That is outside – in the notoriously dark bottom of the Aire Valley. So far, Jack and his "hot beds" have mainly local celebrity status but he thinks he is onto something which could get bigger.

He uses stable muck-out to generate heat under and around his soil-filled growing frames as the winter days start to get longer, from the end of December.

He starts building in the first half of January and planting in the second and even on council allotments at the Marley Stadium, on the Bradford side of Keighley, reckons to grab an extra thousand hours of daylight for his plants in the start he gets on the usual growing season.

It is a technique which goes back to the days of the Roman emperor Tiberius, who insisted on his salads wherever he was, two thousand years ago.

"People talk about Victorian hot beds but it's a lot older than that," says Jack, 59. "It went with having a lot of horses. But then the motor car started to edge out the horse and when electricity came in, it was relatively cheap to heat the soil with cables. Now it's not, of course."

He grew up in London but decided on a career in farming and gardening at the age of 15, when he went to visit some relatives – "real peasant farmers in Belgium". In 1999, he was hired to run allotments and teach gardening for The Cellar Project, a Bradford-based charity organising work for people with mental health problems. And he took the opportunity to start experimenting with hot beds.

One of his inspirations was a book from 1908 which explained to the English how the French were making money out of supplying them with fresh veg in the depths of winter – and how to copy them.

C.D.McKay, author of The French Garden In England, marvelled at a three-acre market garden near Paris which employed eight men and a horse and spent 100 a year on extra manure. It was making 600 an acre – when 400 was a decent middle-class salary – from an output including "20,000 lbs of carrots, 20,000 lbs of onions, radishes and other veg sold by weight, 6,000 heads of cabbage, 3,000 cauliflowers, 5,000 baskets of tomatoes, 5,000 of choice fruit, 134,000 heads of salad ..."

The French secret was in maximising use of the heat and Jack does the same. By the time his radishes are ready, lettuces are coming through from the same soil. Carrots are coming up behind the lettuces and will be ready in May, with cauliflowers close behind, grown from seeds which were started indoors in October. Potatoes, turnips and spinach, aubergines, tomatoes, courgettes, pumpkins, all get enough of a kick start to ripen naturally in the real summer. The final flourish is a melon crop from a combination of hot bed and polytunnel.

Once the heat is used, it is time to spread the fermented muck to make a rich base for conventional growing. The garden in the 1908 case study produced 250 cubic yards a year of spare loam for sale.

Jack's vegetables are used in the Salt Cellar Caf at the Cellar Project's hq in The Old School, Farfield Road, Shipley, BD18 4QP, and some are sold on a Thursday and Friday through Bradford Whole Foods at the same address.

Timing is everything, says Jack. The growing medium can heat up to 65C (150F), which is hot enough to kill seeds. The trick is to plant after it has started to cool.

In order to work properly, the heat heaps must be laid in layers, on a bed of leaves, not simply tipped. And they need area as well as depth.

Jack has tried all kinds of containers, but has concluded he needs at least around eight feet by six (about two square metres), with as much depth as he can get.

A lot of time is spent moving the polythene covers on and off the growing frames, to control the air temperature around the plants and to let in rain.

Jack points out that a lot of his labour could be mechanised and he is sure there is commercial potential in the science he has revived.

He pays 25 a load to have stable waste delivered, because it is the right mix of air, manure and urine but he has made the system work with forest waste instead of straw and with cattle and sheep and poultry bedding.

His experiments continue when he gets home to Hipperholme, where he is working on a book. He is also talking with The Cellar Project about running courses for the general public. Call 01274 586474 to register interest.