Most fashion designers appear in the final moments of their shows, give a demure bow to the audience and sidle off. Betsey Johnson, however, does cartwheels down the catwalk. Even if you know absolutely nothing about her design philosophy, that alone provides a strong clue that she isn't of the black, minimalist school of clothing. Exuberant, irrepressible, dazzling - the adjectives apply as much to her dresses, which are available in Lane Crawford, as to her personality. After 20 years running her own business, she is still a powerhouse of wild energy. Even better, she's discovering success and fame with her modern vintage look in - whisper it - her more focused middle age. Johnson will be 56 in August. For this interview in her sunny New York studio, she is wearing her red hair in a high cascade on top of her head, a purple slip dress cut low enough to show off a well-preserved bosom across which a green lightning flash has been tattooed (in Hong Kong, as it happens, many years ago), and her long fingernails are bright emerald. She is undeniably eccentric but nobody survives more than three decades in the unforgiving rag trade without at least a morsel of commonsense. One fashion writer has labelled her 'the hippie who never grew up' but asked to comment on this description, Johnson remarks dryly: 'I was never a hippy. Hippies took a lot of drugs and never worked, right?' And she has certainly worked. In 1964, she won Mademoiselle magazine's Guest Editor contest (a previous winner, in 1953, was the angst-ridden poet Sylvia Plath which just goes to show how all-embracing of personality type that competition could be). A year later, Johnson was a designer and had become thoroughly immersed in the New York zeitgeist. She married John Cale of The Velvet Underground and Edie Sedgwick, that poor little rich girl who became a symbol of drug-wasted beautiful youth, was her fitting model. In the 1970s, as well as creating for the label Alley Cat, she was trotting backwards and forwards to Hong Kong, designing a junior line called Star Ferry ('very groovy') and getting tattooed ('in a funky arcade up from The Peninsula'). She divorced Cale and married again. In 1975, her daughter Lulu was born and in 1978, so was Betsey Johnson the label, which she still owns equally with her business partner, Chantal Bacon. Lulu grew up to be a sleek girl who likes Prada (she used to cry when her mother appeared in public in her trademark sartorial efforts), and is now in charge of the company's higher-priced, more conservative Ultra line which was launched in 1996. Her mother admits Lulu's presence has brought a degree of accessibility to the label which had been missing. 'If Lulu wears it, you know it's a saleable thing. If I wear it you know it's not.' This, evidently, cannot be true but she has had to walk a tightrope between her own hippy inclinations and the spirit of commerce. Many years ago, for instance, she designed a dress which, er, grew when it was watered. She rolls her eyes when presented with the memory. 'Oh, there were noise dresses then, fluorescent bikinis in silver cans, all that. At the beginning, I was designing too close to what I was wearing. And what I was wearing was a leotard with a little skirt . . . in the 60s what was fun was the editorial, oh my God, what fun. 'But now it's fun to have your business working, to know that people are wearing your clothes. It's been in the past three or four years, somehow, that the business has grown tremendously.' The explanation for this is surely that the zeitgeist has caught up with her once more. Frocks, which used to be a bad word in any girl's fashion vocabulary, are now what every decently dressed girl must be seen to wear. Soft, clinging feminine lines, which were so popular in the 1970s, are back, along with the vintage look which Ms Johnson has espoused all her life. And florals are blooming endlessly which is good news for a designer whose signature is the rose. Still, she's torn between delight and mild remorse at her success. 'It's a delicate thing. I do feel that there are phases of being overly merchandised. I sometimes feel that it's getting too saleable so I'll say 'Yes, those 10 pieces are not saleable but, hey, we've got to have them for the me-customer.' 'I believe in middle-America conservative dressing but I don't want to make those clothes. I've always meant something special to the industry and I've fought to hold on to that niche.' At the same time, her peculiar niche is filling up with younger designers who have had the good sense to spot it. 'Years ago, I was much more alone in my work. My look is the look of a lot of companies now, and you're only as good as your last sale. 'I know that my customer is basically between 20 and 30, so I have to watch movies, MTV, stay in touch. It's keeping myself alive, like Madonna. I have to figure out how to make it work when I'm not the new kid on the block.' Madonna is an appropriate example: the singer's stylist is about to come into the showroom and choose some clothes for a Rolling Stone magazine cover. Indeed, the list of female celebrities who shop at Betsey Johnson is long enough and diverse enough - Susan Sarandon, Winona Ryder, k.d. lang, Gillian Anderson - to prove that Ms Johnson is still getting it right. These days her customers have more accessories to play with; this is the 1990s and she's already gone the signature perfume and beauty product road. 'I'm dying to break into the home category. That's really exciting. But I still feel that we'll be unique. We're not Tommy, Calvin or Donna.'