IN THE GARDEN SAY IT SLOWLY, AND YOU'LL LEARN TO LOVE IT.

Byline: JOSHUA SISKIN

Nassella tenuissima. (Na-SELL-a ten-yu-ISS-i-ma) Nassella tenuissima. Nassella tenuissima.

Say it over several times. Linger over the esses. If there ever was a plant whose description matched the sound of its name, Nassella tenuissima would be it.

Nassella tenuissima is a tall, wavy, graceful member of the grass family. The slightest breeze makes it quiver, creating an undulating, S-shaped movement through the garden, a counterpoint to the proverbial rustling of the leaves in the trees.

Nassella (Stipa) tenuissima is variously known as Mexican feather grass, fine stem tussock grass, Texas needle grass, pony tails, and angel's hair. Its plethora of common names is an indication of the fond esteem in which it is held among a growing number of plant enthusiasts.

It is native to Mexico, Texas, and New Mexico but has been exported to the four corners of the earth. It grows best in full sun to light shade and develops as dense fountain-like masses of ultrathin green threads woven together. Its silver to gold inflorescences, depending on the sunlight and vantage point of the observer, are visible from June until September. In the fall, the plant turns to the color of straw.

As in the case of many other ornamental grasses, Nassella tenuissima should be watered regularly to look its best and grow fastest, but the soil it is growing in should be allowed to dry out thoroughly between waterings. Poorly drained soil or over watering will surely result in fungus problems. Crown rot, which occurs when water accumulates where grass blade meets grass root at the soil line, is usually lethal.

Mexican feather grass grows to about two feet in height. Like ornamental grasses in general, it should be drastically cut back in late winter just prior to the resumption of growth in the spring. This plant is recommended for erosion control on slopes because of its modest water requirement and its ability to re-seed itself.

In fact, it does a spectacular job, if not too good a job of re-seeding itself. And there's the rub. Just when you thought you had found a plant that could do no wrong, you learn about its down side. In certain parts of the world, Mexican feather grass has been labeled a noxious weed. In Australia, importing it is a violation of law. Because of its self-propagating ability, Australian sheep farmers fear that it would quickly jump over the backyard fence, invade and then conquer thousands of acres of pasture land before it could be brought under control.

With premonitions of droughts to come, Nassella tenuissima is only one of many ornamental grasses that have been popping up in gardens and landscapes throughout Los Angeles this summer.

A popular design concept sets off burgundy fountain grass (Pennisetum setaceum ``Rubrum'') against blue oat grass (Helictotrichon sempervirens), blue rye grass (Leymus arenarius ``Glaucus''), or blue moor grass (Seslaria caerulea). Variegated grasses are also popular, with gold and silver banded pampas grasses (Cortaderia selloana ``Gold Band'' and ``Silver Comet''), white- and yellow-striped zebra grasses (Miscanthus varieties), and variegated reed grass (Calamagrostis x acutiflora ``Overdam'') leading the way.

Lemon grass (Cymbopogon citratus) is used in Asian cooking and will grow its best in a garden of partial shade. Sugar cane (Saccharinum officinarum), which grows quite easily in the Valley, is another edible member of the grass family; its almost woody canes provide a sweet snack to chew on throughout the summer months.

Tip of the week: Grasses may be used in wide borders around a more water- needy lawn or flower bed. You do not have to give up your favorite garden features to accommodate ornamental grasses. If you have dry spots in your garden that the sprinklers barely seem to reach, you might consider planting ornamental grasses in those areas.