GARDENING; APRIL SHOWERS CAN - AND DO - BRING MAY FLOWERS.

Byline: Joshua Siskin

The unexpected April rain early this week was a pleasant surprise. Not only was the rain helpful in germinating seeds and evenly soaking the root systems of all garden plants, but the accompanying gray skies highlighted the colors found in a memorable collection of exquisite trees, shrubs and vines that are currently in bloom.

The most brilliant yellow in the entire botanical world is seen in the flowers that cloak the golden trumpet tree (Tabebuia chrysotricha) at this time of year. It is a phosphorescent yellow which, if stared at for prolonged periods of time, may lead to spells of giddiness. The golden trumpet tree is native to the tropical rain forests of South America, as is the pink trumpet tree (Tabebuia impetiginosa) which is also flowering now.

These Tabebuias (taba-BOO-yas) are sparse, slow-growing trees that eventually reach a height of 25 feet. They barely need to be pruned and are immune to insect pests and diseases. For thousands of years, the native people of the Andes have made the inner bark of the pink trumpet tree into a medicinal tea that is useful in fighting infections, shrinking tumors, numbing aches and pains, and strengthening the autoimmune system in general.

I have seen three lilac bushes blooming in recent days, clear proof that these cold-climate harbingers of spring can be made to flower in our own subtropical desert as well. ``Sunset Western Garden Book'' lists five species of lilac (Syringa) which will flower in the Valley; ask your local nursery to order them if they are not in stock. Visit the Descanso Gardens in La Canada for the best local display of blooming lilacs.

Flowering quince (Chaenomeles) is a vivid bloomer whose most well- known varieties have waxy tomato-red flowers. Like the tabebuia, the flowering quince blooms before its leaves have appeared. There are nearly two dozen varieties of flowering quince, from compact shrubs 3 feet in height to 10-foot-tall trees. Flower colors include a wide range of pinks and reds as well as white.

When you think of Mandevilla vines, you no doubt fixate on the pink-flowering, rather finicky ``Alice du Pont'' variety. It is one of those plants that looks great in a container in the nursery but changes character after being planted beside a lamppost or next to a fence. In the nursery it has silky green leaves and unblemished deep pink flowers; after being planted in the ground, its leaves become chlorotic and infested with spider mites while its willingness to flower becomes highly questionable.

Enter a different sort of Mandevilla vine from Bolivia known as Mandevilla bolivensis. Although cold sensitive, it makes the perfect vine for a protected arbor or patio setting. Its large white flowers with yellow throats are presently in bloom, as they will be on and off throughout the year.

A number of e-mails, reflecting the urgency of spring garden concerns, has lately been received, including the following:

From Jim Wildman: ``Three years ago, I set out seven birds of paradise, facing north, shaded by a large olive tree. The largest birds have grown to more than 6 feet tall with no flowers. Would more sun make them produce?''

Birds of paradise (Strelitzia reginae) are somewhat tricky to grow, especially as you move into the hotter, more western Valley communities such as Woodland Hills and West Hills. In the East Valley, birds of paradise will flower their best with a half day of sun, while in the West Valley, they will burn when exposed to more than three or four hours of direct sun each day. In any case, your north-facing location, while encouraging healthy foliar growth, has squelched your plants' inclination to flower. You should also be aware that there is enormous variability among birds of paradise as far as their flowering capacity is concerned.

From Dixie: ``For years I have raised a back yard full of poppies, half of which were fancy varieties. About two years ago, among the fancy types, I started seeing smaller plants with leaves colored from yellow to rust. At the nursery, they said I had a virus. This year, the virus is rampant in my fancy poppies. Is there anything I can do?''

I am assuming you are talking about Shirley poppies, which self-sow with the greatest of ease. Your fancy or hybrid poppies are more susceptible to viruses than your more conventional, wilder types. There is nothing you can do to stop the virus, which can be passed through the seeds, other than to pull every one of the tainted plants. Poppies are visited by aphids and by thrips, two insect groups that are well-known as vectors (transmitters) of plant viruses.