A FRIEND WHO`D just been in Toronto to auction her new book mentioned in a letter that she`d overheard a conversation between several editors at a major Canadian publishing house. They were discussing gardening books. They were talking about them, she said, as the perfect sales-boosting vehicle for the new environment- and ecology -conscious age, which for many of us seems lamentably overdue. If the crop of gardening books here is any indication of what is to come, they may have a true and worthy growth sector on their hands in more ways than one. I like gardening books. Whatever form they come in and they come in many sizes and formats -- they`re nearly always useful. Most of the ones listed here are useful and beautiful, and even if they`re never taken off the coffee table, it`s healthier for our souls to have books around that propose ways to make the world a better place than to have books about how to fill our faces, make ourselves privately fitter or smarter, or books that make nearly every place on the planet more glamorous and appealing than our own backyards. Because I lean just a little more toward the utility of gardening books than to their beauty I do the same with gardens -- I`ll talk about the most useful books on our list and then move to beauty. The prize for the most useful book goes to The National Arboretum Book of Outstanding Garden Plants (Simon and Schuster (General), 292 pages, unpriced), by Jacqueline Heriteau. It`s an American book, and some of the 1,700 plants listed won`t thrive in Canadian soil. But it`s beautifully organized and illustrated, and intelligently yet not too technically written. For avid gardeners, this book will be indispensable. Mark Cullen`s A Greener Thumb: The Complete Guide to Gardening in Canada (Penguin, 252 pages, $29.95 cloth) doesn`t come close to being a complete guide with only 252 pages (try 2,052 pages). It`s heavily laden with colour photos, but it`s well organized and quite well illustrated. It isn`t in the class of the Reader`s Digest Illustrated Guide to Gardening in Canada, and I found the section on vegetable gardening short and uninformative. If you live in the suburbs and want to garden just a little and make it look pretty, this book will do the trick for you. Fred Dales Toronto Star Outdoor Garden Book (McClelland & Stewart, 192 pages, $14.95 paper) is exactly what you`d expect from the gardening columnist of a major Canadian newspaper. It`s crustily incisive, aimed more at problem-solving than aesthetics, filled with useful lists, and doesn`t cost much. If you use it, you`ll probably get what it says you`ll get, but you won`t win any gardening awards with it, not even in your own mind. It won`t be of any help outside Southern Ontario, either. The New Organic Gardener (Old Bridge Press (Firefly), 269 pages, $19.95 paper), by Eliot Coleman, is aimed, like all organic gardening books -- and there are a lot of them -- at those who take gardening as a quasi-religious activity rather than an aesthetic pleasure. Unfortunately, the illustrations are inadequate and it`s excessively optimistic about the problems city dwellers face in trying to garden organically. On the other hand, it`s extremely clear on the subject of small-scale commercial organic gardening, going so far as to offer advice about how to fire unproductive workers. Organic gardening is a growth industry, so if you`re thinking about going into business, it may be useful to you. Peter Loewer`s A Year of Flowers: Your House and Garden in Bloom from January to December (Rodale (McClelland & Stewart), 254 pages, $19.95 paper) comes from a publisher known for bolo ties, recipes for squash pie, and testimonials for rototillers. Surprise! This is an interesting and well-illustrated book without a single recipe for how to eat your flowers once you`ve grown them. Harrowsmith and Camden House are obviously building a series of relatively inexpensive gardening specialty manuals. All three of the books here -- The Harrowsmith Gardener`s Guide to Ground Covers, edited by Jennifer Bennett, The Harrowsmith Gardener`s Guide to Spring Flowers, and The Harrowsmith Guide to Rock Gardens, both edited by Katherine Ferguson (all from Firefly, each 96 pages and $9.95 paper)- are distinctly Canadian, well written, and adequately illustrated. And there are more than these three to be had. I recommend them highly. Somewhat upmarket and more expert-oriented are the Globe Pequot Press (McGraw-Hill Ryerson) volumes on classic garden plants. Begonias (96 pages, $26.95 cloth), by Brian Langdon; Auriculas (96 pages, $26.95 cloth), by Brenda Hyatt; and Magnolias (144 pages, $26.95 cloth), by J. M. Gardiner, will be of use primarily to wealthy and land-rich aficionados or professionals. But Herbs (144 pages, $26.95 cloth), by Simon and Judith Hopkinson, is frankly the best book of herb gardening I`ve ever seen. It`s encyclopaedic, but it`s also written very clearly and simply. If you want to grow your own herbs, and there`s no reason why anyone with a garden larger than a pot on a balcony can`t, this book is a real, if expensive, find. Elizabeth Murray`s Monet`s Passion (Pomegranate (Firefly), 115 pages, unpriced) is one of those once-in-a-decade gardening books that will be of profound interest not just to very serious gardeners but also to art lovers, architects, and anyone else with an abiding interest in beauty and the productive powers of human imagination. It is a study of the exquisite gardens designed by Claude Monet in Giverny, France, around the turn of the century. Monet spent 40 years designing the gardens and using them as a subject of his paintings. They remain one of the wonders of the gardening world, and Elizabeth Murray does a remarkable job of revealing the genius of their design and use of colour. This book will take your breath away in about 10 different ways and, for the really avid, is worth any price under $100. Beware that it doesn`t end up costing you a trip to France to see for yourself also rating special mention in the beauty category is The Passionate Gardener (Little, Brown, 150 pages, $29.95 cloth), edited by Miranda Innes, which is a kind of British all-stars of gardening -- along with their gardens. It`s a lower order of beauty than that of Monet`s Passion, but these gardens will make many gardeners drool anyway. Among the 23 all-stars included, interestingly, are the movie star Dana Wynter and the wonderful Germaine Greer. I had always wondered where Greer got those carpenter`s hands -- now I know. Not a useful book for beginners but indispensable for gardening-book collectors, and there are such folks. Last and least, we have an oddity that is so odd it demands, comment. It is Elizabeth`s Garden: Elizabeth Smart on the Art of Gardening (Coach House, 77 pages, $14.95 paper), edited by Alice Van Wart. The book consists of three rather off-the-wall essays on gardening -- 14 pages in all -- by a famous and recently deceased Canadian writer. The rest of the slim volume is Ms. Smart`s gardening journal, mainly lists of plants planted, garden tasks accomplished, or tasks to be completed. I know this woman has become a cultural hero, and it`s not nice to be disrespectful to the dead, but my Yugoslavian neighbour across the alley knows four times as much about gardening as Elizabeth Smart ever did, and I or anyone could learn more about gardening from a five-minute conversation with her, broken English and all, than they will from reading this trivial and rather ghoulish bit of exploitation.