Within 60 seconds of setting eyes on me Joni Mitchell has started telling me about her dreams. I am spared details, but she insists that they have been unnaturally lucid, something to do with being far from her Los Angeles home.

The grande dame of rock's singer-songwriter tendency had been staying for a few days in Scotland, where an exhibition of her paintings was showing in an Edinburgh gallery. Every inch the modern Renaissance woman, Mitchell is no dilettante in this regard, and her paintings, especially the abstract acrylics, have been known to fetch as much as $60,000 (Pounds 30,000). By the time I have sat down, she is in full flight, explaining the logistics of the display.

"You had to hang it like a necklace. You figured out the centre piece, and dealt with the paintings like beads and when it was completed it looked like a mural, quite handsome. I like that sort of process: film-editing, sequencing an album, juxtaposition..."'

Dressed with expensive, functional elegance in an Issey Miyake dress and black leggings, she eats biscuits, drinks coffee, smokes heavily and sits with the composed posture you would expect of a "truant yoga student". She speaks in a breathless rush, fixing a subject in her mind's eye and then describing it with bundles of colourful phrases.

Her next exhibition will be of her photography. Last summer she travelled with her camera and her husband, jazz bass-player Larry Klein, through the Canadian locales of her itinerant childhood: the towns of Fort Macleod, Calgary, Maidstone, North Battleford and Saskatoon, scattered on the vast prairie lands of Alberta and Saskatchewan.

There she photographed "the lakes of my childhood; the farm machinery; the grain elevators, which we call prairie skyscraperstall wooden structures, painted bright green and orange and burgundy with yellow roofs." Then she "sandwiched" the images with a series of self-portraits. "You get a road going up my nose, and there's a field of wheat with my husband standing where my nose is and my eye becomes a moon; oh, there's some really profound stuff."

Quite so, but it is in her primary role as a musician that Mitchell has long been famed for her ability to come up with the really profound stuff. One of the more wholesome torchbearers of Sixties hippiedom, she wrote the "Woodstock" anthem (a hit for Crosby, Stills, Nash & Young and Matthew's Southern Comfort) without actually attending the festival. She was never a performer who relied on either a militant or a decorous image, although she did stick a picture of her naked bottom on the cover of her 1972 album For the Roses (an image removed from later pressings).

Instead she exploited her femininity in other ways, writing about intensely personal relationships from a woman's perspective, but shunning the drippy love-song conventions. She reached an apogee of rigorous self-analysis with her 1971 album, Blue, a ravaging emotional critique of the post-Aquarian age, which set the course for a succeeding generation of bohemian chanteuses from Suzanne Vega to Tracy Chapman, Michelle Shocked and beyond.

But while her openness may have left her vulnerable, she was nobody's victim. Experimental, bold, intelligent and original, she transported her folk textures to a jazz environment with a series of albums culminating in her 1979 Mingus, a collaboration with, and tribute to, the ailing bass player, Charles Mingus, who died soon afterwards. The recording was a move which she now believes lost her a large chunk of her audience.

"I've pretty much been stricken from the history of rock'n'roll in America," she says. "They think I'm a traitor. It's as if I was a Baptist and now I'm a Catholic. However, I am being written up in some classical music textbooks. They include me with Stevie Wonder, Duke Ellington and others as 20th-century composers. I am one of the pioneers of music with a broader harmonic sense than rock'n' roll, but I don't fit into any of the handy pigeonholes. That's why it's taken 20 years for me to spawn imitators, and even they have a hard time getting started, the poor dears."

Mitchell is now 47 and, like many artists of her generation, she lives in high expectations of Armageddon just around the corner. Her interest in Native American Indian and Aborigine folklore confirms her belief that technological man is a dangerous meddler whose time is nearly up. It is one of the reasons she has opted out of motherhood.

Her commercial status has held steady for two decades, but has dwindled in real terms relative to the vastly expanded market for recorded music. She released just four albums during the Eighties, each of which sold about half a million copies. The last one, Chalk Mark in a Rainstorm, featured guest appearances by Billy Idol, Peter Gabriel, Wendy & Lisa, among others, but her exclusion from the mainstream continues.

Her new album, Night Ride Home, is not so much a bid for converts as it is an updated restatement of first principles. "Cherokee Louise" and "The Windfall" are in her classic folk-tinged mould while there is a chirpy quality to songs such as "The Only Joy in Town" and "Ray's Dad's Cadillac" which recall the lightness of touch which she brought to her 1970 hit, "Big Yellow Taxi", the first certifiably eco-friendly pop song, and still her only single to chart in Britain.

A darker force is evoked on "Slouching Towards Bethlehem", an intriguing attempt to set W.B.Yeats's apocalyptic poem, "The Second Coming", to music. The recording of it was completed last June, before American troops were committed to the Gulf, but she accepts that the images of the lion and the desert have acquired a fresh resonance in the wake of subsequent events.

Joni Mitchell's Night Ride Home (Geffen GEF24302) is released on February 25.