St Thomas’s Church of England primary school in Groombridge, Kent, is as pretty and leafy as they come. Plenty of white weather boarding, ancient oak trunks, hanging baskets, and even a small greenhouse round the back. The perfect place, you would think, to nurture children who will be gardeners one day.

It is certainly trying. Last year it won a competition run by the Royal Horticultural Society for a garden on the theme of harmony designed by eight to 11-year-olds. This month their garden was built and put on display at the Hampton Court Flower Show.

The driving force behind the school’s entry was long-time parent helper Caroline Tully, who, with 30 volunteer children, completed the design in just one term. The school was at the time in the middle of an Ofsted inspection and a major rebuilding programme, so the staff were fully occupied. Mrs Tully had at her disposal two lunch breaks a week, a fortnightly local trip, and several voluntary Saturdays in school with parents and children. She could also draw on her own passion for gardening and the degree in environmental education she is taking at the University of Sussex, which concentrates on the use of school grounds.

The RHS competition is judged not only on the design submitted, but also on an accompanying portfolio of work. It involves a lot of effort, as shown by the fact that, of the 2,000 schools that enquired about the competition, only 33 entered.

There is a requirement to show how the work relates to the national curriculum. So bird pudding was fine for food science, building a bird table “absolutely brilliant” for design and technology (according to one young lad), and translating into metric the imperial dimensions in the competition brief was a useful task in mathematics.

But St Thomas’s also made a great effort to involve the local community in the project, both at the school itself and in visits to local people and places. Two head gardeners, from Groombridge Place and Penns in the Rocks, came in to talk about design, history, colour, organic gardening, tools and safety at work. The children visited a beekeeper and were shown by another expert how to design a bird table. Someone brought in chickens to draw, and talked about the eternal cycle of manure and bone meal. There was even an aromatherapist involved, who explained about the history of plants in medicine, and why for instance we use mint in toothpaste.

But it was the garden visits which really inspired the children, even though the competition was running in the winter months. They were most excited by the ancient “drunken” topiary at Groombridge. Later, Caroline Tully had them making their own instant topiary with moss and chicken wire. “Great fun, but they were much faster on Blue Peter,” says Caroline.

The children were asked if they would like to write up their impressions of the visits. This produced willing work and an obvious feel for their subject: “Each garden seemed to have a world of its own and the real world no longer existed, like a magic dream,” wrote Chloe Kenward, aged 10.

The boys especially liked productive gardening, which led to eating things. One boy now grows vegetables at home, and brings them to school to sell. Another was passionate about construction, and enjoyed measuring up for a wheelchair path in the school grounds so that they could cost it and chase sponsorship.

The girls were self-confessed flower-lovers. One now particularly enjoys flower painting and arranging. She enters her work in the village’s horticultural society shows, which many of the children have joined, swelling its numbers and reducing considerably the average age.

The children’s garden won a bronze medal at Hampton Court, and you can see why. It might not have been at the cutting-edge of modern design, but for children’s work it was remarkably good. There was a fountain of sculpted hands delivering water into a pebbly watercourse which ran down to a pond. There was a formal vegetable and herb garden with clipped box edges, and a bed of delphiniums. The garden was entered through a fine pair of iron gates and the path flanked by flower beds and funny little scallops of lawn, which would be a nightmare to mow and the kind of impractical idea you would expect from first-time designers.

Caroline Tully was pleasantly surprised to win the RHS competition last year. “We didn’t enter to win. We just wanted to do the work,” she says. There was plenty of backing from headteacher Andrew Raven, also a keen gardener. He is as aware as anyone else that you cannot produce fabulous school gardens with the children, because of the holiday gaps. But you can give the children a sense of ownership of the grounds, and a full sense of their value and potential. He saw the competition as good seed corn, with a useful, tangible objective.

Now the school has been rebuilt and Ofsted is gone for a while, Mr Raven has hopes that the whole of his staff will be able to share this sense of ownership of the grounds, and make use of them for as many aspects of the curriculum as possible.