GARDENING : AUTHORS' 20-MINUTE LIMIT RAISES THORNY ISSUE.

Byline: Joshua Siskin

``You shall spend no more than 20 minutes a day working in your garden, and your tasks will be only those that you enjoy.''

This is a commandment spoken by the twin gods of the late 20th century: the god of impatience and the god of fun. It is also the mantra of Tom Christopher and Marty Asher, authors of ``The 20-Minute Gardener,'' (Random House; 1997).

The authors, true to their own creed, do little gardening themselves - barely worth a 20-minute browse in a bookstore - and have little credibility for any true lover of plants.

``Why 20 minutes a day?'' one of the authors asks. ``That's as much time as anyone I know has to devote to anything besides work ... That ought to be enough time to maintain a garden.''

Clearly, I am living in another world, a place where millions of people are devoted to rose gardens, flower beds and green lawns - a place where people actually enjoy caring for plants and gardens for more than 20 minutes at a time.

What I resent about this book is the implication that gardening - or any activity that is not related to career pursuits - can only be justified if it can be done quickly. Really, it doesn't matter if you spend two hours or 20 minutes or two minutes every day in the garden.

But why try to quantify and delimit gardening - done simply for the purpose of bringing more beauty to the world - in the first place? You get the feeling that, for the authors, plants are ultimately more of a nuisance than a joy. You come away from this book with the impression that the authors, unlike most gardeners, are selfish people with no values other than expediency and convenience.

They take pride in their collection of ``graveyard roses,'' propagated from cuttings taken from rosebushes growing next to headstones. ``A couple of generations ago, it was the custom to plant a rose by your mother's grave - and even now, 50 or 75 years later, many of these sentimental plantings still survive ... Any rose that can flourish year after year without any help, obviously likes the local climate and soil - and is self-sufficient enough to be perfect for the 20-minute gardener. You can't buy graveyard roses, so the only way to get one of your own is to take a cutting and root it yourself ... Common sense dictates that you should take cuttings only from roses growing on gravesides old enough that the survivors aren't still paying visits ... It is embarrassing to be discovered in the act of grave robbing by the bereaved.''

These self-confessed grave robbers have learned nothing from their forays into the garden. If they had taken the time to study the natural processes at work there, they would have learned humility and respect. A gardener who takes cuttings from graveside rosebushes is like a president who invites campaign donors to sleep in Lincoln's room at the White House; both exploit the memories of beloved people for personal gain.

It is understandable that one of the authors would mention the hardy orange (Poncirus trifoliata), as his favorite hedge plant. ``This plant's greatest benefit is the sense of security it can provide. It bears needle-sharp, 1 to 2-inch long thorns all along its stems - nobody pushes his way through a hardy orange.'' If I were robbing graves, I certainly would want to create a sense of security around me, too.

While the authors believe you should avoid doing garden chores yourself and delegate them, if at all possible, to others, they have nothing but contempt for in-house gardeners of large institutions. This antipathy is based on one of the author's experiences at Columbia University, where he was in charge of three gardeners who refused to follow his orders - I can't imagine why - and hid out in a campus boiler room.

On an entirely different and upbeat note, I recently received a letter from Arlene Delaney, who teaches fifth grade at Oxnard Street Elementary School in North Hollywood. Upon her invitation, I visited the school and was pleasantly surprised to find several elaborately landscaped planter beds. I learned that Ellen Tremmel, another teacher at the school, had been working with her students for a number of years in beautifying these beds.

Growing harmoniously in partial shade are sages, sword ferns and false heather (Cuphea hyssopifolia), as well as the exquisite ``Black Beauty'' heliotrope (Heliotropium arborescens), which has dark violet flowers and blackish purple leaves. Tremmel says that she brings her students out to weed and water every chance she gets, attested to by the health and beauty of the school garden.

Tip of the week: Bert Lasky of West Hills wonders what to do about rabbits that regularly invade his flower bed. The ``Ortho Problem Solver'' recommends constructing a 2-foot-high fence, made of 1-1/2-inch chicken wire, around the bed. The wire should be buried 3 to 4 inches under the soil with a flap of wire bent outward from the bed. Another idea is to plant lettuce around the flowers. With any luck, the rabbits will nibble on the lettuce and leave the flowers alone. Dusting blood meal around plants also may deter rabbits; reapply blood meal after a rain, since it must be dry to be effective against rabbits.