Reading along in THE INVITING GARDEN: Gardening for the Senses, Mind, and Spirit (Holt, $40), I suddenly came upon this provocative sentence: “Gardening is not a hobby, and only nongardeners would describe it as such.” For a writer as genial as Allen Lacy, this qualifies as a shot across the wheelbarrow. “There is nothing wrong with having hobbies,” he goes on, “but most hobbies are intellectually limited and make no reference to the larger world. By contrast, being wholeheartedly involved with gardens is involvement with life itself in the deepest sense.” Indeed. For could it ever be said about, say, bridge that the way you play a hand has implications for the environment, American cuisine, biological diversity, drug policy and national identity, not to mention the nature of time and the meaning of place? “A garden, whether we know it or not,” Lacy writes, “connects us to the world in many strange and wonderful ways.”

This notion that the garden is a path out into the larger world is a peculiarly American idea. For most of history, and in most of the rest of civilization, gardens have been conceived as walled-off refuges from the world, places of escape rather than engagement. Maybe that’s why Americans never went for the hortus conclusus, preferring to bring down the traditional walls and fences so that our gardens might, in every sense, connect. Our lawns and even our compost piles have a politics, and moral considerations color our choice of plants (useful or ornamental? native or exotic?) and horticultural practice (chemical or organic?). True, it can get to be a little much—and occasionally it does, as in a couple of this season’s more ideologically minded garden books. But when a writer is as deft as Allen Lacy, the connections traced between a cramped yard in southern New Jersey and such far-flung concerns as species extinction, the symbolism of the American front yard, the migration of plants, the act of naming and the rub of seasonal and biographical time in a garden can be thrilling to follow.

The best of this season’s garden books all share this inclination to find a world of meaning in even the most modest garden, though Lacy takes the prize for finding the greatest variety of meanings. Only when you get to the very end of “The Inviting Garden,” which unfolds as unhurriedly as a Saturday morning schmooze over the back fence with a particularly amiable neighbor, does the ambition of Lacy’s project emerge. He has written nothing less than a defense of gardening, in the classical sense of that word, the one that we associate with Philip Sidney. Lacy’s method is to show us the beauty of gardening’s three faces in turn: its ability to delight the senses (with a chapter each on the Big Five), instruct the intellect (taking up plant hunting, naming and symbolism, as well as American landscape design) and elevate the spirit (chiefly by planting us in time and place). Cynthia Woodyard’s ungushy photographs effectively underscore Lacy’s ideas.

But although “The Inviting Garden” is a genuinely philosophical book (Lacy was in fact a professor of philosophy long before he established himself as the dean of American garden writers), it doesn’t have a didactic, pushy or theoretical sentence in it. Lacy’s writing is a model of clarity and modesty, and all of his insights are rooted in the soil of his long experience growing specific plants in a specific place. (Whatever the horticultural equivalent of being well read is—well planted?—Lacy surely is that.) Both the new and the old gardener will find much to think about here, and to savor.

Laura Simon makes a different set of connections in DEAR MR. JEFFERSON: Letters From a Nantucket Gardener (Crown, $23). As the title suggests, her interest is historical, and her method epistolary: the book takes the form of a half-dozen letters to Thomas Jefferson, the secular patron saint of American gardeners. (“No occupation is so delightful to me as the culture of the earth,” he wrote in a letter most of us can recite by heart, “and no culture comparable to that of the garden.”) The conceit, which for the most part she manages to pull off quite nicely, allows Simon to write casually about doings in her own Nantucket garden (her passion, like Jefferson’s, is for vegetables) and to wander down some of the byways of American garden history. Simon follows in the tradition of Eleanor Perenyi and Katharine S. White, writers who departed from their accustomed lines of work to offer a single book about gardening, an avid testament by a confirmed yet highly knowledgeable amateur.

In Simon’s case, the garden book is a break from the writing of historical novels, and this background serves her well: the historical passages are swift, sure-footed and fascinating.

Those that work best are the ones in which Jefferson himself plays a role, like the history of the tomato (which he helped introduce to America—or, really, reintroduce, since its roots are Mexican); the development of mail-order seeds (Bernard M’Mahon, father of the seed catalogue, was T.J.’s Burpee) and the fate of the vegetable varieties that Jefferson grew at Monticello, some of which are still grown as heirlooms, while many others—like the Ravensworth pea he used to rave about—have been lost forever. Here planting and then tasting a tomato Jefferson cherished becomes an exercise of the historical imagination.

The conceit starts to creak only when Simon needs to impart information about Monticello her correspondent well knows, such as the length of the kitchen garden (1,000 feet) or the “interminable procession of friends, relatives and rubberneckers who would appear on your Palladian doorsteps.” At first her efforts to describe the modern world—McDonald’s, environmentalism, health fads—to someone living 200 years ago seemed a stretch, but after a while you get used to it, and start to appreciate how writing to Jefferson allows Simon to sneak up on our own times, see them afresh. Her account of the contemporary American kitchen garden, brimming with the food plants of a dozen different cultures and historical periods, not only would have wowed Thomas Jefferson, whose garden and table were as radically cosmopolitan as he was, but also succeeds in convincing the reader that we are indeed in the throes of “yet another gardening resurgence.”

STALKING THE WILD AMARANTH: Gardening in the Age of Extinction (Holt, $25) is, as the subtitle gives fair warning, a book with an agenda. Janet Marinelli, director of publishing at the Brooklyn Botanic Garden, bids us to see the connections between our yards, teeming with exotic plants and smothered in lawn, and the worldwide decline of biological diversity. Our yards are part of the problem, having obliterated native habitats and contributed to the homogenization of the world’s flora, yet, reconceived, they might also become part of the solution. This is a tendentious premise, yet Marinelli is so reasonable, and such a breezy writer, that the reader is happy to follow her deep into the thickets of horticultural politics.

As the Communist Party was to the 30’s or the Vietnam War was to the 60’s, so native plants are the defining political issue to contemporary gardening. Do you believe it is morally responsible to plant a tea rose or burning bush in your yard at a time when so much of our native flora is threatened by the proliferation of such alien species? You might have thought those particular horses are already out of the barn and well down the road, as indeed they have been since 1492: perhaps a third of the plants one encounters in the landscape of the eastern United States, from the roadside day lilies and Queen Anne’s lace to the lawn grasses and the apple trees, are alien species. (Virtually everything still green in October is European in origin, having evolved under milder autumn circumstances.) Even so, the advocates of native-plant gardening contend that we’re obliged to undo the damage, and our yards are a good place to start. (In the interest of full disclosure, I should mention that Marinelli and the author of the next book here take me to task for a 1994 article in The Times Magazine in which I criticized native plantmania and drew a connection between nativism in horticulture and politics.)

In the most persuasive part of Marinelli’s gentle polemic, she argues that garden design has always reflected a civilization’s understanding of nature, yet our own esthetics have so far failed to keep pace with the lessons of ecology. (Garden practice is another matter: organic methods have become increasingly well established.) Most contemporary garden design can still be classified as either classical, expressing in its formal geometry a rationalist view of nature’s essential order, or romantic, modeled on our subjective experience of nature. What’s needed now is an ecological garden, one that “won’t try to imitate, like classical gardens, what nature is, or, like romantic gardens, what it looks like,” she writes. Rather it must “act like nature, must do what nature does.”

That this is easier said than done is amply demonstrated in PARADISE BY DESIGN: Native Plants and the New American Landscape (North Point/Farrar, Straus & Giroux, $25), by Kathryn Phillips. Phillips, a journalist (she is the author of “Tracking the Vanished Frogs: An Ecological Mystery”) rather than a garden writer, has written a book that aims to be to landscape design what Tracy Kidder’s “House” was to carpentry. Her unobtrusive narrator trails Joni Janecki, a young California landscape architect, as she designs gardens for the Sands family in Montecito, the Hewlett-Packard Company’s corporate offices in Palo Alto and a public park in Salinas. Janecki is deeply committed to using native plants in her work, though the story of the Sands job suggests what an uphill struggle it is to persuade clients to give up on the Old World plants, lawns and all the other trappings of landscape tidiness that still dominate American dreams of paradise. The reader is surprised at the end of “Paradise by Design” when the Sands actually ditch most of Joni’s ecologically sensitive design in favor of a big old lawn with a sprinkler system.

Luckily for Phillips, Hewlett-Packard and the city of Salinas keep the environmental faith, and we get to look on as a series of habitat gardens take shape. (Though because there are no illustrations, we can only guess what they look like.) Phillips is a very good journalist, and she’s done her homework, not only on the habits of native and invasive plants but on the history and practice of landscape architecture and the workings of the American nursery industry (there’s a fascinating section on the marketing of the new carpet rose). The book makes you realize just how little legwork goes into most writing on gardening in this country, and it’s refreshing to read some genuine reporting on the subject instead of the usual first-person philosophizing. Phillips has been unfortunate in her choice of a hero, however, because much as we come to root for plucky Joni Janecki as she battles the forces of horticultural reaction, she doesn’t have what it takes to carry this book on her shoulders. Maybe it has something to do with being such a visual person, but Janecki is virtually inarticulate, both about the value of native plants and the process of design. “I can see it and I can see what it looks like,” she explains (if that is the right word) in the heat of designing the Sands’ garden, “but I don’t really know what it is. It would help to know that, I think, especially as I go along.” Agreed. Fortunately for us, Phillips keeps Joni’s lines to a wincing minimum and fills the second half of her book with rich, well-reported digressions on the tensions between the business and ecology of the American landscape.

Lest you conclude all gardeners have forsaken human pleasure for the sake of planetary health, I heartily recommend spending some time in A TUSCAN PARADISE (Stewart, Tabori & Chang, $35), a dazzling photographic essay that takes the coffeetable gardening book to a new level. Irresistible though they may be, picture books on gardens are seldom more than skin deep, the horticultural equivalent of fashion photography, if not pornography. Marina Schinz, whom readers, or lookers, may remember from her stunning work in “Visions of Paradise” (1985), has opted this time around for depth over breadth, choosing to train her lens on a single not-famous garden—Valle Pinciole, near Tuscany’s border with Umbria—over a period of three years. The result is a remarkably intimate portrait of a place that captures not only its considerable beauty, but also the rhythms of its seasons, as well as the everyday life and backstage labor that ordinarily don’t make it into published gardens. (What a novelty it is to see the gardener, Gian Paolo, pruning the boxwood hedges, clippings scattered beneath his plumb line.)

Valle Pinciole, which is the creation and weekend retreat of two Roman friends of Schinz, is a virtual encyclopedia of garden styles, a densely layered landscape of hedged outdoor rooms, pergolas, mazes, orchards, rosewalks (395 roses are in residence), olive groves, an orangerie, a white garden, an herb garden, a Japanese cherry garden and an English Jekyll garden—indeed, just about everything but a native plant garden. Think of it as a habitat garden for classically educated humans.

It would be easy to dismiss “A Tuscan Paradise” as yet another volume of Mediterranean fantasy for the Peter Mayle and Frances Mayes crowd. But Schinz’s accomplishment has been to make her subject seem romantic and completely real at the same time, to render a Pierre de Ronsard rose in such a way that it recalls the sumptuousness of all roses and yet is never anything less than its heartbreakingly specific, timebound self. Her scrupulous eye reminds us how a garden is a real place before it is a representation, which suggests another sort of connection our gardens encourage us to make, the one between the here-and-now of a place and the there-and-then of what Mirabel Osler once called the infinity of gardens.

Which reminds me that Osler’s 1989 book, A GENTLE PLEA FOR CHAOS (Arcade, $19.95), is one of two out-of-print classics of modern English garden writing that we’re fortunate to have back on the shelf this season. Not especially gentle, Osler’s volume of essays sent a blast of fresh air through the stuffy rooms of the English gardening world when it was first published. This is less a handbook of advice (though what there is of that is excellent) than a miscellany of “thoughts” that have “sprouted while I have been deadheading roses, visiting gardens or buying a pair of socks.” Starting out from the garden Osler made with her late husband, Michael, in Shropshire, the narrative comes and goes as freely a cat, touching down on everything from garden design to weather, the quirks of particular plants and gardeners, botanical illustration, laziness, the compulsion of water, garden visiting and even television westerns. This is a smart, spirited, gorgeously written and above all funny book, so open-minded (her outlook is refreshingly international), personal and passionate as to make one wonder if Mirabel Osler is really an English gardener after all.

By contrast, Graham Stuart Thomas’s TREES IN THE LANDSCAPE (Sagapress, $35) is English to its roots, an authoritative treatise on “how tree planting makes landscapes happen,” written in the great tradition of Humphry Repton and Capability Brown. Thomas, who has spent the better part of 30 years supervising the restoration of gardens for the National Trust, looks at big trees as if they were so many tubes of paint in the hands of the picturesque master, focusing on how the particular form, texture and color of the various species contribute to the look and mood of a landscape. This is gardening in broad strokes for the long haul, and while “Trees in the Landscape” reads as if it has been written for gardeners with lots of land and money and help, even the gardener planting a sapling would do well to consult this wise and handsomely illustrated volume about the trees that connect our gardens to the future.