GARDENING : HEARTY WEEDS CAN THRIVE JUST ABOUT ANYWHERE.

Byline: Joshua Siskin

Every morning when I drive down Van Nuys Boulevard, I notice a wonderful plant growing in the median strip. It has huge white trumpet flowers and grey green felty leaves.

No one planted it there. It's not supposed to be there. If it were not for some imperfect concrete work when the median was poured, this fantastic specimen would not exist. Somehow, in the indomitable style of so many opportunistic species, this plant found a way to grow. The seed from which it germinated was probably washed into a crack of the concrete during last winter's rains.

The plant in question is jimsonweed (Datura meteloides). It is one of the easiest plants to identify, even from a distance, on account of its luminescent white clarion blooms, which can reach 8 inches in length. It is arguably the most ornamental weed you'll find on this continent.

It's just uncanny how perfectly suited this plant is to the Van Nuys median strip it calls home. It tightly hugs the narrow, raised concrete surface, gently spilling over the sides. I'm anxiously monitoring its nonchalant growth into the street, where it will be conveniently crush-pruned by the tires of passing cars.

This particular species of jimsonweed (there are several) is native to California and the Southwest, making it unique among the weeds found in this part of the country. Virtually every other weed in our gardens, it seems, comes from somewhere else. During the last century, weeds were brought to California by the people who immigrated here from Europe, Asia, and the Eastern United States. In those days, people often traveled with bags of seeds, so that they could start growing crops as soon as they were settled; certain weeds live in close association with certain crops, and so weed seeds - many of which are too minute to be noticed - were unavoidably mixed in with the crop seeds brought in by the new settlers. Also, soil was used as ballast on ships, and this soil was filled, of course, with weed seeds native to the lands from which the ships set sail.

The word jimson is a corrupted or shortened form of Jamestown. It was in colonial Jamestown, Va., that a species of jimsonweed was noticed and described by Capt. John Smith. He also wrote of the demented behavior exhibited by those who tasted its fruits. As a member of the potato or nightshade family, jimsonweed contains alkaloids that can be medicinal, hallucinogenic or lethal, depending on the amount consumed.

Although its leaves are typically malodorous, the flowers of many jimsonweed species (Datura spp.) are sweetly fragrant. Flowers may appear in double or even triple form, as if two or three trumpets were stacked on top of each other. In some cases, these flowers will appear folded during the day, opening fully only at night. Like other night-blooming, white-flowered plants, jimsonweed is pollinated by moths.

Garden variety Daturas have, in recent years, taken the genus name of Brugmansia. Angel's trumpet (Brugmansia candida) is an arborescent plant that can grow up to 10 feet in height. Brugmansia versicolor has varieties with either yellow, orange, or pink tubular blooms.

Unlike jimsonweed, which thrives in blistering full-sun exposures, Brugmansias cannot take unmitigated Valley heat. They do best when given half-day sun and will bloom on and off throughout the year under such conditions. They also grow well in containers.

Brugmansias can put on an enormous amount of growth in a single season, and must be pruned annually to keep them under control.

Marian Hoover of Canoga Park wants to know what can be done to discourage squirrels from eating her apricots. One tried-and-true solution is to use a Hav-A-Hart squirrel trap. This device (available at Green Thumb Nursery) traps the animal without harming it. You can then take the squirrel to an animal control station.

Robert Doone, also of Canoga Park, wants to know what to do about the nematodes that have proliferated in his tomato-growing area. Nematodes are microscopic, wormlike creatures that kill plants by destroying their roots. One way of dealing with this problem is by selecting tomato cultivars that are resistant to nematodes. The initials ``VFN'' on a tomato seed packet indicate resistance to verticilium (V) and fusarium (F) - which are fungi - and to nematodes (N).

Gardening tip: Now is a good time to prepare your fall/winter vegetable garden. After moistening the soil, cultivate to a depth of 2 feet and improve the soil with as much well-rotted compost as you can find or afford. After creating raised beds - a natural outcome of cultivation and compost addition - moisten again before planting.

MEMO: Joshua Siskin's column appears every Saturday. He welcomes questions from readers. Write to him in care of the Daily News Features Department, P.O. Box 4200, Woodland Hills, Calif. 91365-4200. You can also reach him through this online mailbox: JoshSiskinaol.com.