GARDENING : LEMON GOOD FOR WHAT AILS YOU JOSHUA SISKIN.

If you want to live for a hundred years, it might be wise to grow an herb that has the texture of crepe, the fragrance of lemon and the name of a pretty girl.

According to Modern Herbal (Dover Publications; 1971), the Englishman John Hussey lived to the age of 116 imbibing tea, made from this herb, mixed with honey. For 50 years, Hussey sipped lemon balm tea for breakfast.

Lemon balm. The very words are soothing. Balm is an abbreviated form of balsam - any sweet resinous oil derived from a plant, be it a rock rose, a pine tree or an herb. And lemon is a botanical scent that everyone seems to like; it's as though there were something inherently medicinal about it.

Melissa officinalis, is the scientific name for lemon balm. Melissa is the Greek word for honeybee and refers to the fact that bees ``are delighted with this herb above all others,'' to quote John Gerard, a 16th-century herbalist.

Officinalis means ``of closets or shops,'' especially apothecary shops. When a plant name includes the word ``officinalis,'' a medicinal use is understood, as in Rosmarinus officinalis (rosemary) and Salvia officinalis (garden sage). Incidentally, the best volume currently available on the etymology of plant names is Stearn's Dictionary of Plant Names for Gardeners (Cassell Publishers; 1996 paperback edition), by William Stearn.

In Gerard's day, there was no distinction between the disciplines of botany and medicine. In order to call yourself a doctor - or more precisely, a healer - you were required to be an expert in the curative properties of plants. By the same token, an herbalist was someone who made sick people well through prescribing the appropriate tincture, decoction, carminatie, vermifuge or tea - all derived from plants. Gerard himself was both a surgeon and a garden superintendent.

Like many of its cousins in the mint family (Lamiaceae), lemon balm is not difficult to grow. In the San Fernando Valley it prefers a partial sun exposure and, to look its best, regular watering. To keep it compact and lush, lemon balm should be cut to ground level at summer's end. The plant may live for up to six years and is easy to propagate from shoot tip cuttings.

A garden of lemon-scented plants is eminently feasible in Los Angeles. For trees, you would plant the lemon-scented gum (Eucalyptus citriodora), the most popular eucalyptus for landscaping on account of its alabaster trunk and essentially vertical growth habit. True, eucalyptus are susceptible to breakage and even toppling over, as we witnessed in the recent windstorm that swept our city. Still, this is a tree with a distinctive look and smell, providing a precious landmark for remembering a certain place or a certain time.

For tall shrubs, you would grow lemon verbena (Aloysia triphylla). It is generally agreed that this plant has the strongest lemon fragrance of all. Its habit of growth is willowy and its white flowers, though not spectacular, are worthy of a second look. Like lemon balm, this plant must be well-watered in the summer to look its best.

As a low shrub or ground cover, you would utilize the lemon-scented geranium (Pelargonium crispum). Unique among scented geraniums, this species has rippled leaves set tightly along the stem. Absent the odor of its leaves, this would remain a highly prized landscape ornamental.

In the light shade of tall trees, lemon grass (Cymbopogon citratus) would find its place in this uni-scented garden. People make the mistake of planting lemon grass in too much sun and are rewarded with burnt-edged clumps. Too much shade, on the other hand, will stymie growth of lemon grass altogether, eventually killing it.

For the vegetable garden, grow French sorrel (Rumex scutatus). The leaves of this plant, when chewed, make a refreshing lemony pick-me-up. You don't actually eat the leaves, but chew them, enjoying the juice.

As the year draws to a close, it's time to recognize a gardener who saw an incredible amount of growth in 1996. This year's award goes to Lola Tillman of West Hills, who grew a cherry tomato plant to a height of 12 feet and a Bigger Boy tomato to a height of 6 feet. Her secret: She used a Valencia orange tree as a support for the tomatoes.

Her explanation?

``I smile when I say this,'' she says, ``but all of these tomatoes are in between rose bushes, cosmos, chrysanthemums, lilies, vinca and hibiscus plants, and I tell everyone that the roses and the flowers - with the bees, butterflies and hummingbirds all around - talk to the tomatoes and that is why they have done so well and grown into the orange tree so tall.''

Tip of the week: To transform your poinsettia into an outdoor ornamental, locate it next to a south or west facing wall, since it is somewhat cold sensitive, in well-drained soil. Ideally, delay planting until March, when the danger of frost has past.