LEEDS, YORKSHIRE, ENGLAND — 'I LOVE climbing plants," says Frieda Brown.Her voice, in spite of years living in the northern county of Yorkshire, is still firmly stamped by her early days in the East End of London. "I don't know why I do. They just appeal to me. And when I started this garden, I could see that it was going to need climbing plants." That was in 1963. Neither she nor her American-born husband, Joe, had ever done any gardening before. And even then their garden was their's only by courtesy of the state. Their home is on a council (or municipal) housing estate, and typically the gardens tacked onto such houses receive scant attention from the tenants. Why should they do anything with them? After all, they don't belong to them. Joe and Frieda Brown's garden (and one of their sons is now buying their house and garden for them) is the glorious result of not for one minute going along with such a laissez faire attitude. Mrs. Brown calls it a "secret garden," and she and her husband have made for themselves an extraordinary degree of privacy in it, on a site where privacy was not something the planners considered of the least importance. "And of course," she goes on reminiscing in their living room as we shelter from a brief bout of late-afternoon rain, "I knew nothing about anything, and the only climbing plants I knew about were roses." She worked, before retirement, for the Social Services in Leeds, organizing thousands of meals a day for housebound and handicapped people. Her husband was in building, in selling, in industry, before taking early retirement. Today the Browns know a great deal more than they did once about hundreds of different kinds of garden plants and how to grow them. They have light, well-drained soil. At one time, before it was built on, this land had been allotments (community gardens). Dig down and it's fertile all the way. No clay. As it has turned out, climbing roses are not given very much space in the Browns' now-mature garden. But another kind of climber is - to the point, perhaps, of obsession - and that is clematis. "It's a garden that needs climbers to give it a third dimension," says Mrs. Brown. More than 70 different varieties of clematis burgeon and flower third-dimensionally here. The really important thing, in growing them, she says, is to water them well. The Browns sink lengths of plastic drainpipe near the clematis roots and frequently fill them with water. "You cannot overwater them and you cannot overfeed them," is her motto. She says some people make the mistake of planting clematis and "then expecting i t to grow by itself." Many of their clematises are at their very best in summer. The number they have might not seem excessive in a large garden. But this garden is, by any standards, extremely small. For many years it was, in fact, only 48 feet long, though two further expansions lengthways have extended it to 120 feet. Its width is charmingly variable, but at any point it would take no more than five seconds to stride from one side to another - if, that is, there weren't so many precious and damageable plants in the way. The Browns have capitalized on these small measurements in three notable ways. First, by using their climbing plants for height and background. Second, by growing plants above ground in a collection of containers, many of them used for fuchsias - stone troughs, old sinks, urns, pots, and so on - placed with great forethought. Third - and this is where Mr. Brown's expertise comes into its own - by excavating, mounding, and building up a great many ground levels. For years, they have collected pieces of th e local sandstone (none of it has ever cost them a penny, much of it coming from demolition sites), which Joe sensitively shapes with hammer and chisel: He uses this stone for paving, for steps, for terracing, for rockery work, and for edging the two ponds. This beautifully crafted and built stonework gives the garden a strong structure. THE garden has appeared on television a number of times. It has won all kinds of awards. Violinist Yehudi Menuhin even played in it. Every summer, from the end of June to the beginning of August, coaches arrive full of enthusiastic garden society members, visitors from the United States or Holland or Canada - not to mention photographers and journalists. "By appointment, of course," cautions Mr. Brown. And there are open days for charity as well. Nearly a thousand people now come to see this tiny strip o f horticultural delight every summer. The Browns thoroughly enjoy their visitors. "Because I just love talking gardens," Mrs. Brown says. And she loves to show people "what you can do with a 'little back bit. I gaze out of their newly enlarged window at their "little back bit," over the flourishing group of unusual ferns, over the little round pond, my eye following the steppingstones strategically placed like a backbone in the narrow ribbon of grass, which is bordered on each side by a wondrous array of flowering summer plants. Here are poppies and penstemons, lilies and love-in-the-mists, tall campanulas and low-growing geraniums, climbing tropaeolum with brilliant orange-red flowers, veritable bouquets of brodiaea with its blue-violet flowers, a small variety of agapanthus still budding up, large allium seed heads, and asters promising color later in the season. And, ramping and falling and smothered in open star-flowers or hanging bells - violet, blue, yellow, pink, white - like a miniature tribute to the Hanging Gardens of Babylon are clematis, clematis everywhere. The part of the garden nearest to the house, up to the iron arch that stands (covered in clematis) at what was originally its farthest boundary, is primarily a herbaceous garden. Mrs. Brown is an enthusiastic member of the Hardy Plant Society, and her collection of plants comes from an annual auction held by local members, from Horticultural Shows, from specialist nurseries, and from small growers. One nearby grower cultivates old herbaceous varieties - though she thinks she has pretty much acquired what he has to offer by now. Visitors are another source of plants. Some shyly, some boldly proffer little gems as gifts from their gardens, receiving something special from the Browns' garden in return. I admit to thinking before visiting this concentrated treasure-house of plants that I would probably have seen all there was to see in about an hour. But I must have stayed well over three hours and still felt I'd missed plenty. Mrs. Brown says she often finds the same thing: She can spend hours in the garden, and when she comes in she thinks, "Oh - I forgot to look at such-and-such a plant!" The exhaustive pleasure of the garden, for an enthusiast, is that there are no plants used just to fill spaces. Every single one is chosen advisedly, and every one it seems is a special source of interest and affection for its owners. Though there are lots of plants the Browns would like to include, the small space requires considerable discipline. The larger herbaceous plants are out, and so are most shrubs, except for alpine shrubs or dwarf conifers. Just a few trees make a background at the far end - a rowan and a sycamore. A favorite Japanese maple is carefully pruned to keep it within bounds. Beyond the arch is an alpine garden, terracing (making optimum use of the space, with dozens of small plants now flourishing where once there was just one old plum tree), narrow, winding sunken pathways, a raised pond with a fountain, and a minute chamomile lawn, much trodden by visitors. Farther on still is a spring garden, which is the only place early bulbs are allowed. Mrs. Brown points sardonically at a plant rampaging all over the shady ground here. "Worst thing I've ever done," she observes. It is a lamium (a creeping ground cover) clearly out of control. They also made a mistake very early on when they planted two "Russian vines" recommended by a garden center to "clothe" a new rustic fence Joe had made. This is one climber Mrs. Brown no longer loves. Known also as "mile-a-minute," it is an insane grower. It eventually destroyed the rustic fence. But mistakes - which every gardener makes - are now cut to a minimum. The Browns have learned exactly what sorts of plants are most suited to their "little back bit" of magic.