In the space of two hours last week I learned much more than I had previously known about roses and about a group of artists and writers who were particularly partial to them — and to each other. My education came courtesy of my old friend Robert Mattock, a rose-grower and gardens expert, who gave a fascinating talk at Asthall Manor on Wednesday, as part of the on form 2014 sculpture-in-stone exhibition, focusing on the men — and they were all men — whom he considers the unacknowledged pioneers of the wild, as distinct from the formal garden, after which he guided his audience, in the company of Asthall’s head gardener Mark Edwards, around the manor’s glorious garden, itself a notable modern example of the type — Cotswoldiana, in Robert’s naming — where he drew our attention to the many varieties of roses it contains.

The Jamesian length of the foregoing sentence is intentional, for Henry James was one of the men — mainly rich, expatriate Americans — who composed what is now known as the Broadway Group. Others included his literary contemporary Edmund Gosse and the artists Francis Davis Millet — later a victim of the Titanic’s sinking — Edwin Abbey, John Singer Sargent, Edwin Blashfield, Alfred Parsons and Laurence Alma-Tadema. They were named for the pretty Gloucestershire village — then a remote, scarcely visited backwater — where their summers were spent, a focal point being Millet’s Abbots Grange, restored with the help of William Morris.

Abbey wrote at the time: “We really do have a gay summer, pretending to work and sometimes working . . . until four, then tennis until dinner time, and after dinner, dancing and music and various cheering games in the studio, but mostly dancing.”

‘Gay’ was le mot juste because, Robert told us, many of the men were homosexual, albeit closeted. He said: “Homosexuality was, of course, illegal during this period and surely one, perhaps the only, form of expression for their emotional sensitivity was through their art.”

Three of the group — Parsons, Millet and Abbey — lived together and entertained sociably at 54 Bedford Gardens in London. Guests included William Robinson, “for too long credited as the father of ‘the wild garden’,” Robert told us, on account of his best-selling book of that name.

Mattock claimed that Gravetye Manor in West Sussex, Robinson’s world-famous exercise in the style, was to a large extent the inspiration of his friend Parsons. “Robinson invited Parsons to ‘lend advice’, but advice is an understatement; the Englishness of the Gravetye landscape is Parsons through and through.”

This Englishness had been noted in his depiction of country life as illustrator for Harper’s Magazine.

“Was it there,” Henry James asked, “that Mr Parson’s learned so well how Americans would like England to appear? The England of his pencil . . . is exactly the England that the American imagination, restricted to itself, constructs from the poets, the novelists, from all the delightful testimony it inherits.”

Robert paid deserved tribute to Julian and Isabel Bannerman, who redesigned the gardens at Asthall Manor for its owner Rosie Pearson.

He said: “Their response to the site was ‘founded upon observation of what they saw, trying to see a different level, informed by a lifetime of fascination with the natural world and of human intervention in that world’.

“How very Broadway, how very Henry James and Singer Sargent, and certainly very Alfred Parsons. Have we here at Asthall a Wild Garden, an advance on the Arts & Crafts movement, Englishness, or rather, I believe, a contemporary view on Cotswoldiana?”

Those wishing to consider the question should see Asthall for themselves. On form 2014 supplies the opportunity until July 6. Go to onformsculpture.co.uk for details.

My own visit was notable for the sudden appearance above us of the menacing, but sculptural, form of a giant B-2 Stealth Bomber, one of two — their call signs Death 11 and Death 12 — on a visit from the US to RAF Fairford. Sabre-rattling to Russia, apparently, over Ukraine.

The sight led me to recall how the private view at a previous on form was enlivened when the Red Arrows roared overhead, tri-coloured smoke in their wake, as the church bells rang. We thought Rosie had arranged it specially.