GARDENING : SAMPLING SUCCULENT WONDERS OF SAN MARINO.

Byline: Joshua Siskin

Last weekend's annual plant sale at the Huntington Botanical Gardens in San Marino was something to behold, once you got out of the parking lot.

At the Huntington, there is a remarkable collection of infrequently encountered plants in the parkways separating the many rows of parking spaces. A write-up about these plants alone could fill several pages.

In making the journey from your car to the main garden, you are likely to encounter the following: a double-flowered pomegranate with striped petals; a multitrunked Chilopsis tashkentensis tree, which is a hybrid between the catalpa and the desert willow, with pink trumpet flowers; a green and cream variegated Coprosma kirkii ground cover; a compact version of Italian jasmine (Jasminum humile); and a mounding plant with scabiosa-type leaves and lavender, staticelike flowers.

But the parking lot plant that may stop you dead in your tracks is a clump of what looks like a 7- or 8-foot-tall yarrow. Investigations will lead to the conclusion that while, like the yarrow, it is clearly in the daisy family, it is in all probability a member of the genus Athanasia, which means immortal in Greek. I assume this botanical name refers to its flowers, which, like those of the yarrow, would appear to stand up admirably in an everlasting flower bouquet. In the meantime, Athanasia can confidently lay claim to the title of ``tallest ground cover on Earth.''

One cool cactus

At the east entrance to the plant sale, I see what looks like either a Henry Moore sculpture or a python that is digesting a wart hog. It turns out that this is a succulent by the name of Mammillaria compressa. It is being sold for $1,500 and would make a wonderful gift for the cactus gardener who has everything.

Once inside, I immediately see that the cactuses and succulents are far more popular than I could have ever imagined. You might think that people in a dry climate like L.A.'s would seek to escape from the baking heat and cultivate lush oasis gardens. Yet it appears that, above all, we are a practical people and are interested mainly in water-thrifty plants.

After walking around for an hour or so, I keep noticing that one display is perpetually encircled by a small throng of people. As I approach, I see the two drop-dead beautiful succulents that everyone seems to want to know more about. The first is Pachypodium rosalatum, a so-called Madagascar palm with clear yellow flowers that could compete with those of any other plant - including the canary trumpets of the Tabebuia - for brilliance. The man who grows these, Bill Hagblom, is also showing off what are, quite obviously, the most stunning plants of the whole show: the Adeniums.

Hagblom is selling a 3-foot-tall Adenium for $200 but, believe me, it's a good deal. Picture a succulent elephant's-foot trunk base with many branches criss-crossing away from it. Each branch is covered with periwinkle-shaped flowers that are either red or pink or a combination of the two colors. The plant looks like a bonsai even though it may grow up to 1 foot per year.

Hagblom is selling both traditional and dwarf Adeniums. Since all of his plants are grown from seed, he cannot help but create new hybrids in the course of propagation. Adeniums, however, are not self-fertile, and cross-pollination between plants is required if they are to produce seed.

Growing Adeniums

There is nothing tricky about the culture of the seldom-seen Adenium. The soil mix of this container-grown plant should be one-half perlite or pumice and one-half potting soil. Mulch the soil surface with pumice or fine gravel so that the soil dries out evenly. Water only when the soil is very nearly dry, as indicated by a moisture meter - available for around $5 at a garden center. However, do not let the soil go bone dry, as it is difficult to rewet. In 80-degree weather, the plant should need to be watered about once a week. With each watering, fertilize at one-quarter the recommended strength. (If Miracle-Gro recommends 1 tablespoon per gallon of water, use one-quarter tablespoon per gallon instead.)

Adeniums should be grown outdoors. The only problem is that they can die when temperatures dip below 40 degrees. To protect against this possibility, put plants in a greenhouse window during the winter, or at least bring them inside at night during winter months.

I spoke to Shirley Kerins, who organizes the Huntington's plant sale each year. She is also curator of the Huntington herb garden and manager of plant production. She takes her hat off to Theresa Trunnelle, the Huntington's main plant propagator, who can ``root a broomstick.''

Thirty percent of the plants on sale are propagated by the Huntington. The rest come from specialty nurseries and plant societies in Southern California, but there is still room for new growers seeking an outlet for their plants. ``We are always on the lookout for people growing unusual plants in good condition that are flowering at the time of our sale,'' Kerins said. ``We also accept cuttings and seeds from those who would like us to increase the selection of plants that we propagate and sell.''

Before leaving, I spotted an Athanasia parvifolia in a 4-inch pot. I don't know if it's the same species I saw in the Huntington parking lot, and will be carefully watching to see how tall it grows. I paid $2.75 for this specimen, which is only 6 inches tall, but it won't seem like much if Athanasia grows even half as magnificently as its counterpart in San Marino.

Tip of the week: If you missed the big May sale, don't despair. The Huntington has a lecture on a horticultural topic followed by a plant sale the first Thursday of every month. There is also a four-day sidewalk sale of books and plants in November. For more information on the Huntington's garden events, call [phone].