GARDENING : PLANTS THAT SURVIVE WINTER MAY BLOOM LIKE GANGBUSTERS.

Byline: Joshua Siskin

At 9000 Winnetka Ave. in Northridge there is a surprising and curious site: A blood red trumpet vine is blooming its head off. No matter that it is the middle of winter and this plant normally starts to bloom in the spring. No matter that we recently had our coldest cold spell in nearly a decade. For this blood red trumpet vine, it may as well be May.

While the cold we experienced was lethal or at least destructive to many tropical and subtropical plants, it was - and will prove to be throughout this year - a flower-inducing tonic to others. Many plants require a period of winter dormancy in order to flower in the spring and summer. Dormancy does not necessarily mean leaf drop, which happens to be the most obvious sign of dormancy's onset in deciduous plants. Evergreen plants, which include nearly all shrubs and ground covers found in Southern California gardens, as well as most of our trees, simply stop growing when they go dormant.

Dormancy is one of the least understood phenomena exhibited by plants. Research suggests that for plants that originate in cold climates, certain chemical compounds which may induce flowering are synthesized when temperatures fall. For plants from more tropical climates, it could be a period of dryness or cold, or a combination of the two, that triggers dormancy.

For California natives and other Mediterranean climate plants, winter is not synonymous with dormancy. In fact, this is the one time of year when you can water California natives without much inhibition. Soil fungi that come to life as the result of excessive watering in the summer are simply not active during the winter.

The blood red trumpet vine (Distictis buccinatoria) is native to Mexico and has slightly bent red trumpets - buccinatoria means ``crooked trumpet'' - with yellow throats. It has a history of blooming at any time of the year when there is a sudden heat surge, which would explain its flowering out of season during the warm days of early January. Two related trumpet vines are noteworthy, despite their more frost-tender nature and thus their requirement for cold-sheltered locations. One is the vanilla trumpet vine (Distictis laxiflora), so-called because ot its vanilla-scented flowers, which open up in violet and then fade to lavender and white. The other is the royal trumpet vine (Distictis ``Rivers''), which adorns itself with regal purple trumpets that have yellow centers.

Camphor tree trouble

Nick Breit of Canyon Country has a problem that is not uncommon in Southern California - sorry-looking camphor trees. ``Both my neighbor and I have 8-year-old camphor trees with leaves that are always falling off and branches that turn black on the ends,'' Breit wrote. ``The tree looks like it is dying. This has been going on for several years. Where we live, the soil is hard clay and high in salt. When we planted the tree, I cut no corners in soil preparation.''

It is difficult to permanently alter the character of a soil, and I suspect it is the soil that is your undoing - a combination of poor drainage and excess salt, which could certainly bring on the constant defoliation you describe.

Camphor trees are native to areas of China and Japan where the soil is sandy and the rainfall significant. Where you have sandy soil and high rainfall, you are likely to have little soil salt due to leaching or draining away of soil minerals by the rain. No matter how well you amended your soil when planting, the roots of your camphor would eventually reach the salty native soil of Santa Clarita. This could explain why you have been having problems ``for several years,'' assuming the trees were healthy before then. Another soil-related problem could be your pH. Where rainfall is heavy, as in the subtropical climes where camphor trees grow wild, soil pH is typically low and acidic. The the soil in Santa Clarita, on the other hand, is famous for its high, alkaline pH. Plants resist growing in soil whose pH is dramatically different from the pH of their native soil.

All that being said, camphor trees may sometimes look peaked under the best of circumstances. They experience leaf drop in late winter or early spring and shed twigs some time later. It is not unusual to see parts of small branches die. And winter is the season when the foliage of the camphor turns pale yellow, in contrast to the glistening green it exhibits in the warmer months.

Lastly, the camphor tree is especially sensitive to so-called ``weed-eater blight''; a gas-powered string trimmer that rips into the trunk of a camphor will cause slow but certain death to the tree.

Still, the camphor is one of the darlings of every serious tree watcher. Its botanical name, Cinnamomum camphora, speaks the truth about its family connections; it is a relative of the same tropical cinnamon used in breakfast pastries, and its crushed leaves do emit a scent of camphor. After a rain, its trunk has a unique black luster as its new leaves, tinged with red or copper, shimmer in the breeze.