GARDENING : VALLEY NOW READY FOR THE COLORS OF FALL.

Byline: Joshua Siskin

For good horticultural reasons, orange, gold and burgundy are fixed prominently in the mind as the colors of fall.

These are the colors of Indian corn and the colors assumed by leaves of certain trees this time of year. Orange pumpkins and golden squashes ripen in the fall, and burgundy cranberries, plucked from New England bogs, will find their way onto just about everyone's Thanksgiving dinner table.

Contrary to what many people think, leaves do not change their color in the fall by producing something that was lacking in spring and summer. The process of foliar color change is brought on by the breakdown of chlorophyll - the pigment that makes leaves green - to reveal other pigments that had been present all along but whose colors were masked by the chlorophyll. These revealed pigments are known as xanthophylls (yellows), carotenes (oranges) and anthocyanins (deep reds).

For Valley gardens, there is one family of plants that is especially recommended for the color of its autumn foliage. It is the barberry family and is represented not only by the true barberries but by nandinas, mahonias and epimediums as well.

There are more than 20 varieties of barberry (Berberis species) suited for our area. Barberries are shrubs that grow from 2 feet to 6 feet tall and have small leathery leaves, spines, yellow flowers and wildlife-attracting fruit. There are both evergreen and deciduous types, some with burgundy or variegated foliage year round. Most have green leaves that turn orange and red each fall.

Nandina domestica, known popularly as heavenly bamboo, has been intensively hybridized in recent years and is now available in a large variety of sizes and growth habits. The original nandina shrub can reach a height of 8 feet and serve as a barrier hedge or screen. Compact hybrids have a more delicate look and can be found at mature heights of 4 feet or less.

Although nandinas can take some shade, they produce much stronger orange and red coloration in the sun. Powdery mildew also can be a problem where sun is insufficient and air circulation is lacking. To improve air circulation, thin out nandina shrubs annually by cutting selected interior canes to the ground. If you trim a nandina with hedge shears, you will completely change its character, transforming it from a feathery leafed natural art form into a nondescript block of vegetation.

Mahonias can grow in a variety of exposures from all-day to quarter-day sun. Several are native to Southern California, including the rare and attractive Nevin's mahonia, which has all but disappeared in the wild but can be procured through native plant nurseries such as the Theodore Payne Foundation in Sun Valley.

Epimediums are the most shade-compatible members of the barberry family. They are grown as ground covers and are suitable as a companion plant to azaleas, camellias and ferns. Epimedium flowers are violet, pink or white.

Barbara Adams of Reseda wrote me to sing the praises of nasturtium, a plant with orange, yellow and burgundy flowers.

If you are starting a garden with children this time of year, there is no better plant to include than nasturtium. Nasturtium seeds are large, easy to plant, and enthusiastic about germinating in the Valley during the fall.

The flowers of the ground-hugging nasturtium, which will bloom in winter or spring, are edible. They have a peppery taste similar to that of watercress, to which nasturtium is closely related.

The leaves of nasturtium, which are also edible, are round, pea green in color and resemble small lily pads. Nasturtium self-sows and will spread through your garden without a lot of effort on your part.