How about a Late Show for plant lovers?

Every spring the lengthening days and promise of balmy summer evenings produce a heady sense of anticipation in plant-minded people. The long winter dormancy of Britain's hardiest perennial is over, and it is starting new growth: Geoff Hamilton is back on the air. At 8.30 every Friday evening, from late spring until the end of the summer, more than six million people lay down their trowels, hang up their wellies and settle down in front of BBC 2's Gardeners' World.

For sheer professionalism you have to hand it to Geoff Hamilton. Now there's a man, you can't help thinking, who knows how to handle a spade. And not only that; he has the enviable ability to impart just the right amount of information even as he digs. Blokeish without being laddish, informed without being superior, Hamilton pitches himself neatly between Desmond Lynam and David Attenborough in terms of likeable accessability.

Apart from Gardeners' World, there are more than 11 hours of garden broadcasting available every week during the peak gardening months. The quality of these programmes is pretty varied, but in terms of their basic formula they are utterly homogeneous.

This is what happens: a camera crew and jolly bunch of presenters roll up to a garden; the garden (grand or humble, in its prime or in dire need of help) is inspected; there follows a brief interview with the owner or the gardener, supplemented with comment or advice from the presenter(s); more shots of the garden and then everyone goes home or on to the next garden.

Gardening programmes, it would appear, are the undisputed territory of what is known in telly speak as the OB - the Outside Broadcast. And why not? Gardens are, after all, outdoor creations, so what on earth would be the point of having a group of presenters standing around indoors talking about something that was outside? It just wouldn't make sense. Or would it?

Forget the Outside Broadcast. Forget the different location every week. Forget the woolly jumpers and wellies. Imagine instead a studio, decorated simply with two or three huge reproductions of Howard Sooley's photographic plant portraits. A presenter, unashamedly in The Late Show style (a horticultural Michael Ignatieff or Sarah Dunnant is what we are looking for - we are not talking Alan Titchmarsh) introduces three guests, each an expert on the subjects up for discussion; each with something to say in a forthright and informed manner on each other's topics, too. Argument and information would flow in lively debate. There would be a limited use of exquisite and strictly pertinent still photographs in order to illustrate a point or a plant.

The subjects discussed each week would fall into three main areas: firstly, a polemical horticultural issue, such as the wisdom of restoring historic gardens or the future of the Lindley Library would be thrashed out. Next, each guest would present a choice plant which they thought deserved better recognition or to be brought into wider cultivation. And lastly, a book - or books - chosen by the presenter would be reviewed by each of the guests. Like the plants, some of the books chosen would be new on the gardening shelves, others would be old classics, long overdue for reappraisal.

I think there would have to be a competition, too, open to all. The purpose would be to encourage new ground to be broken in the pursuit of imaginative design - a sort of Turner Prize for the garden. Some of the submissions would be outrageous, and letters would be written; questions raised in the House of Commons.

In short, the aim of the programme (called Talking Plants perhaps) would be to present gardening as an art. The presentation of gardening as craft would be left in Geoff Hamilton's capable hands.

And one last thing - it would be on late (not before 10pm), because then you wouldn't have to come in from the garden while the evening is still light.

So what would make this programme work? Two things have emerged from the explosion of interest in gardening over the last decade. In the first place, gardening has got younger. It's not the new rock 'n' roll, but there are far more people in their twenties and thirties with dirt under their fingernails and copies of The Plant Finder by their telephones than ever before. Channel 4 has cottoned on to this, with brave attempts to secure a younger audience with programmes such as Dig and Garden Party. But the irritatingly casual, slightly off-beat approach of these programmes nevertheless continues to stress the craft rather than the art of gardening. Older gardeners feel alienated; younger gardeners feel bored or patronised.

This is because, in the second place, gardening has got more sophisticated. Amateur gardeners are more demanding of themselves, their plants and their gardens. It is rather similar to the way our attitude to cooking has altered since the Fifties. Millions of people have graduated from a diet of meat and two veg and are willing to experiment with new ideas and ingredients. Supermarkets stock things that would have been found only in Soho delicatessens 10 or 15 years ago. Gardeners, too, want similar opportunities to give thoughtful expression to their creativity.

As yet, there is no forum on television for gardening gourmets or iconoclasts, yet their numbers are growing. There are horticultural Gary Rhodes and Damien Hirsts out there whose work needs to be challenged and debated; there is an establishment that needs to be assaulted and defended; and there are some fantastic plants that deserve to be better known.

Six million people watch Gardener's World every week. But I bet there are another six million gardeners who don't.

Anna Pavord returns next week