Editor's choice; Home Ground: A Gardener's Miscellany, by Allen Lacy. New York: Farrar Straus Giroux. 259 pp. $14.95.

''Leisure, slowness, contemplation,'' writes Henry Mitchell, ''these amateur virtues are perhaps despised, but they may underlie the greatest joys of gardening, and of life.'' (''The Essential Earthman'', Farrar, Straus & Giroux,

Allen Lacy, whose writing has something of the sententious fiber of Mitchell (whom he admires and quotes in his book), has a Montaignian side. He professes to lack the ability to follow good advice and points out that ''The problem with much good advice is that it can't be retroactive.''

The flowers of his rhetoric are as various as those of his garden, which ''has come into being through sudden impulses, happy mistakes, and unfortunate accidents, and my own enduring willingness to tolerate ambiguity and to practice procrastination whenever possible.''

Lacy, a professor of philosophy at Stockton State College in New Jersey, writes on gardening for the Wall Street Journal and Horticulture magazine. But he is rather more than a gardening columnist: He is a practitioner of the ancient art of the short essay. Gardening is just the matter of his art. The forms are those of the English language, which, on the evidence, he loves as much as gardening.

He listens to the words: ''Ukruman, Askoot-Asquash, and Fembaby'' is a title of one of the many two-page essays in this book.

If that is the high style, Allen Lacy is equally at home in the low: ''Something Must Be Done About This Shed'' opens with ''No doubt they are all right'' - which is to open somewhat as did Homer, in medias res, smack in the middle.

He is a philospher now, and a gardener, but he was once a kid growing up in Irving, Texas. Shortly after Pearl Harbor his father moved the family from Dallas to a farm on Kit Loan Star Road Continuation (which has a poetry of its own). About that time Allen had a third-grade teacher named Mrs. Leghorn. ''My love affair with horticulture began in the early spring of 1943, on the day I bit Mrs. Leghorn on the ankle.''

Something of the country endures in the sophisticated gardener.

Lacy is sophisticated. He is a master of rhythm; his alteration of short and long sentences, as well as mixing high and low (my love affair with horticulture vs. biting Mrs. Leghorn), and his way with a cliche (''a different kettle of fish emulsion,'' from ''Little Ado About Roses''), reflect, like his garden, his knowledge of flowers and of himself.

In the middle of ''The Miseries of an August Garden'' (which opens by contradicting T. S. Eliot about April being ''the cruelest month''), Lacy can write, ''I wish that it would snow.''