GARDENING : SPLASH OF COLOR WELCOME DURING COLD, GRAY MONTHS.

Byline: Joshua Siskin

Just as demand grows with diminished supply, never are garden flowers more eagerly sought than at this time of year. As skies get grayer and temperatures drop, the sun rises ever lower in the sky and color in the garden is given a justifiably inflated value. In the dark, rainy days to come, color will not only brighten and warm up the garden, but lift the spirit as well.

Around Thanksgiving, English primroses - in red, yellow, blue, purple and white - make their grand entrance into the garden. No flowers have brighter colors than these; they glow with an iridescence unmatched by any precious gems.

They are plants for dappled light like their fellow obconica and malacoides primroses, the latter types available in pastel pink, mauve and salmon.

In the sun garden, pansy snapdragon, calendula and stock (Matthiola) are the annual flowers of choice during the season. Stock was given its unusual name because its flowers grow tightly around the stem, much like clerical collars - also known as stocks - are worn around the neck. The flowers of stock have a pleasantly spicy fragrance.

One of the longest-lasting bedding plants for the cool months ahead is cyclamen. Cyclamen is a perennial tuberous plant that is most often grown as an annual, and is typically discarded some time in the spring.

However, it can last several years in the garden as long as it is not watered during its dormant period in summer. Cyclamen blooms in white, pink, lilac or red. Yet the leaves of some cyclamens - up to 6-inch-wide hearts with decorative white markings - are actually more interesting than the cyclamen flowers themselves.

A perfect companion shrub to primroses or cyclamens in dappled light is the winter-blooming heather, Erica canaliculata, with cultivars that produce delicate pendulous urn-shaped flowers in pink, red and purple.

Native to South Africa, this is one of the few heathers that grows well in California. It has a very long bloom period that traverses the entire winter season. Ideally, its soil should be sandy and acidic, and it should be protected from too much winter cold or summer sun.

It is a fine plant for a patio or balcony that is exposed to partial sun; use a potting mix consisting of 50 percent sandy topsoil and 50 percent peat moss. In the garden, it should face east or north, and be watered with a hose on an as-needed basis. Regular sprinkler irrigation will likely result in its early demise.

One group of plants that will flower throughout fall and winter are the cupheas, which seem to delight in short days and cool temperatures. Cuphea hyssopifolia, or false heather, is a small mounding plant with magenta flowers.

Cuphea ignea, the cigar plant, is a 4-foot-tall shrub with red-orange flower tubes that are tipped with yellow. Growing up to 5 feet, cuphea micropetala has similar flowers, only somewhat larger than those of the cigar plant.

There are a select number of plants whose leaves change colors this time of the year. If you are looking for large trees with colorful autumn leaves, you might want to overlook liquidambar and Modesto ash, two of the most popular choices.

The liquidambar, known in its native Southeast as sweet gum, has sharp lobed maple type leaves that turn beautiful shades of burgundy red, pink and yellow; however, this tree will literally take over the yard with its surface roots, gradually eliminating the possibility of planting anything around it.

Modesto ash, whose leaves turn a lustrous gold before they fall, is a magnet for woolly blue aphids and anthracnose fungus, meaning that its leaves are puckered or crispy brown most of the year. It also has surface roots that lift sidewalks and driveways. Other large trees that turn color in the Los Angeles autumn are tulip tree (Liriodendron Tulipifera,) Chinese pistachio (Pistacia chinensis) and ginkgo (Ginkgo biloba.)

Smaller, more manageable trees whose leaves turn color would include the evergreen pear (Pyrus kawakamii,) crape myrtle (Lagerstroemia indica,) Chinese tallow tree (Sapium sebiferum,) and the smoke tree (Cotinus coggygria.)

None of these trees exceeds 30 feet in height. All should be selected this time of year since fall leaf color varies among the trees of each species.

Three shrubs in the barberry family have foliage that changes color in the fall: Oregon grape (Mahonia aquifolium,) heavenly bamboo (Nandina domestica) and Japanese barberry (Berberis Thunbergii.) Boston ivy (Parthenocissus tricuspidata) is the one locally grown vine whose leaves color up each autumn.

Tip of the week: An anonymous e-mail I received asks about the proper technique for pruning the butterfly bush (Buddleia Davidii.) Like other fast-growing shrubs that flower on and off throughout the year, prune back each shoot as soon as its flowers fade. Just before spring, you can cut back the entire plant to a height of 2 feet or less. Since the butterfly bush flowers on the ends of growing shoots, it must be cut back radically once a year to maximize its flowering potential. Butterfly bush is easily propagated from 6-inch shoot-tip cuttings taken during the growing season.