Of the making of gardening books, there is no end. Three unusual volumes published last year deserve special mention.

"In and Out of the Garden Desk Diary" is a perfect calendar and appointment planner for artistic as well as practical gardeners. The diary is an offshoot of illustrator Sara Midda's celebrated 1981 book, "In and Out of the Garden," a number-one best seller in her native England that sold more than 100,000 copies in this country as well. Both books feature tiny, jewel-like watercolors of flowers and vegetables in dreamy pastels in addition to elaborately lettered aphorisms and proverbs relating to gardening, along with suggestions and warnings often appropriate and sometimes just plain whimsical.

Midda's artistry is rooted in the Pickwickian tradition of supernal nonsense. Each painting and calligraphy of hers is a loving fusion of the familiar and the fantastic, a happy marriage of the fanciful and the useful.

Published simultaneously by Workman Publishing in New York and in England, the 1983 calendar is a spiral-bound hardcover cleverly packaged in a gift envelope that is also handsomely illustrated. It is 96 pages and costs $7.95. Every day and every entry is hand lettered, and each page is luxuriantly decorated. Midda also designed stationery and other gift items to complement the calendar.

At $14.95, "Garden Secrets" is a plain, unassuming book that has a way of impressing you as you read on. Published by Rodale Press in Emmaus, Pa., and written by frequent contributors to Rodale Press' Organic Gardening magazine, "Garden Secrets" is a practical, methodical, no-nonsense guide to growing vegetables, crammed with solid ideas.

Authors Dorothy Hinshaw Patent and Diane E. Bilderback are residents of Missoula, Mont., where they tend their gardens. Patent has a BA in biology and a PhD in zoology; Bilderback has a BS in botany. Their book serves as a quick, painless course in botany, as well as a step-by-step, tip-by-tip exploration of the whys and hows of vegetable growing. Particularly useful are discussions of seed germination and the various techniques of ensuring healthy seedlings.

Each chapter deals with one vegetable family, and is divided into sections dealing with seeds, planting, varieties, harvesting, problems and what the authors call "frontiers"--what researchers are up to. The language is simple, the black-and-white illustrations are workmanlike. The authors do not pontificate: The reader finds out as much about the mistakes they made as about their experiments that turned out to be successful.

"Theme Gardens" by Connecticut landscape designer Barbara Damrosch is an irresistibly attractive book that every ambitious gardener ought to study or at least leaf through for ideas. The brilliantly illustrated, oversize paperback is priced at $10.95, and is a Regina Ryan Book from Workman Publishing in New York.

The author's idea was to examine the history, philosophy, genealogy and topography of as many as 16 different types of gardens, each focusing on a single, intriguing theme: fragrance, colonial, butterfly, moon, children, old roses, Zen, Shakespeare, gray, love, hummingbird, secret, medieval paradise, grass, Victorian and winter.

Each theme garden is defined in word and photograph, in historical time and geographical space; then its potentials are outlined in drawings and blueprints. The chapters have subheads such as Site, Growing Instructions, Additions and Substitutions. Finally, there is a Plant List--a glossary of the plants that might be used to create that particular theme garden.

The large typeface makes for easy reading, and the full-color illustrations on nearly every page make the reader's mouth water. An appendix supplies a plant hardiness zone map, an extensive bibliography, and a theme list of mail-order sources.

Damrosch has a lot of innovative ideas for gardens meant for children, lovers and hummingbirds. Her ideas for a Secret Garden are intriguing. The most surprising themes are gardens that feature different types of grass, the color gray and the metaphors of Zen.