Worse, the criticism has come from one of their number - Nigel Colborn, panellist on Radio 4's Gardeners' Question Time and once a star of the BBC2 flagship Gardeners' World. Worse still, the bulk of readers' letters in the magazine's latest issue show his complaints about gardening on the box are widely shared.
"It's obvious that people feel really cheated by some of the programmes," Mr Colborn said last week. "I seem to have stirred up a bit of a hornet's nest."
While less flamboyant than the week's other media row over the restructuring of BBC news, passions are running just as high. Last Monday, at the RHS's annual autumn reception, tension was never far from the surface, though in the end courtliness prevailed.
"I met John Percival [producer of Gardeners' World]," Mr Colborn revealed, "and he managed to avoid being too abusive."
The Colborn critique ranges wide. He wrote of poor programme structure and bad scripts. Gardeners' World had been "prettied up - seemingly for a 30-ish upper-income viewer in Hampstead". He attacked the "personality syndrome" which saw "a tide of presenters hoping to become gardening pin-ups".
He named no names: "I had a lot of agonising over that but I thought that, if I did, people would say that I'm bearing a grudge because I was dropped from Gardeners' World a few years back." (People are saying that - but not for quotation.)
His targets include a new breed of young screen hopefuls who model themselves on the zany Chris Evans rather than on the authoritative TV gardeners of the past. He is particularly irritated by Bill Chudziack, 25-year- old co-presenter of the Channel 4 series Bloom, soon to return as Bloom Two. "The programme is ravishing visually but marred by a lack of sound information."
Mr Chudziack, head gardener at Craigieburn garden in Scotland, responded: "I was a bit surprised by the attack. Because people see a younger face on TV they assume that the TV companies are doing it as a gimmick.
"I know I've been called the Mel Gibson of the potting shed but I keep my feet on the ground. I'm a serious plantsman. I've even been plant-hunting in the Himalayas."
Jo Readman, the series producer, defended her sparky star. "Bill's a terrific enthusiast. His role is to encourage new, young gardeners. Television has to be based on personalities."
Mr Colborn's rashest attack, aimed at the heart of the horticultural establishment, was on Rosemary Verey, a much respected guru and mistress of Barnsley House in Gloucestershire, which boasts a top two-star rating in The Good Gardens Guide.
Last winter Mrs Verey wrote and presented a BBC2 series called English Gardens. Mr Colborn complained of its "rambling script", adding that viewers were "alienated by the grandeur of the scenery and its inhabitants".
In conversation he went further: "It was that upper-class voice drawling on that really got to me. I don't expect she'll be very pleased when we next meet."
Mrs Verey says she has not read the article and does not know Mr Colborn: "People can say what they like. They always like to criticise things. We can only do our best. I'm sorry that Nigel Colborn, whoever he is, didn't like it, but I'm grateful that he watched it."
Mr Colborn was more cautious in criticising Alan Titchmarsh, successor to the late Geoff Hamilton as the main presenter of Gardeners' World. "There's some presentational affectation but he knows his stuff. Some people were upset when I wrote about Gardeners' World being for Hampstead people - but who else is it for, when Alan has a pounds 28,000 conservatory instead of the pounds 400 greenhouse most of his viewers have?"
The makers of TV gardening programmes struggle to come to terms with the hard truth that gardening is a pastime for the middle-aged and elderly. Robin Kent, executive producer of Channel 4's Garden Party, says most viewers of gardening programmes are over 55.
"We think we do well in reaching a younger age group - but in terms of our kind of programme, `young' means between 45 and 55. Our core audience are not the posh gardeners who belong to the RHS, but ordinary allotment- holders."
Mr Colborn's view of Garden Party is succinct: "It's agony!"
As the growing season nears its end, the row is set to keep armchair gardeners well fired up during the winter.