Gardening : Perennials Put on a Colorful Show : Annuals: Nurseries keep adding new varieties of flowers that can convert garden into year-after-year carpet of color.

Perennials are no longer the new kid on the block, but they still offer the unexpected--a surprising color, an astonishing form--simply because there are so many distinctly different kinds. And nurseries keep introducing new ones every year.

This spring, for instance, one of the largest wholesale growers, Magic Growers, offers more than 200 kinds or varieties in its listings.

Perennials can transform a bed of more ordinary flowers. Try them mixed with annual bedding plants, herbs, small shrubs or roses. Or grow them in perennial borders, all by themselves.

In general, perennials need less water than bedding plants--good news for a dry year--but if you live in an area where water rationing is in effect, this is not the time to plant even the most drought-resistant kinds. You might buy them now while they’re in flower and are readily available, but keep them in their containers through summer, watering them bucket-by-bucket if necessary, so you can plant them in the fall, just before the rains arrive.

In other areas, now is a fine time to plant because they quickly become established in the warming soil. Most flower in spring and early summer, so you can find these at nurseries already in flower, but there are also those that wait until late summer or fall and are just greenery now, so be sure to plant some of these too if you want flowers later on.

Quite a few perennials flower off and on all year if the old flowers are promptly cut off. Those that don’t will decorate the garden with handsome foliage for the rest of summer and fall, and they will be back next spring, bigger and better than ever, because they are perennials after all.

Because they are perennials, be sure to do a most thorough job preparing the soil with fertilizer and soil amendments. Remember, they will be in the garden for at least a few years, flowering much of the time, so they need the best of soil.

Try colored pencils when planning a perennial gardens. Let one inch on your drawing equal one foot and then draw a shape of the approximate size in the appropriate color, and see how the various kinds look together.

The following are “best bets,” perennials that gardeners have discovered do unusually well in Southern California. They are just the tip of the iceberg but even these may not be available at every nursery. For a list of nurseries that specialize in perennials, see the accompanying box.

Border Stalwarts

Plant great swathes for color and bulk. All of these are tough plants that bloom for a long time, and none need a lot of water:

Alstroemeria. World-class cut flower blooms all summer. The strongest are the pinks and purples and they spread to form thickets several feet across. Most about 2 1/2-3 feet tall.

Brachycome multifida . As dainty as a wildflower, this is the perennial version of the annual Swan River Daisy with lilac flowers. A great low filler between taller perennials, spreading to a foot across and blooming all the time.

Centranthus . Also called valerian, this one is so tough it grows in vacant lots. Blue-green leaves make small, slowly spreading thickets 3 feet tall. Flowers white or rose and always in bloom.

Coreopsis . Tough golden-yellow daisies at their best inland, where days are hot, though the one named Sunray is good anywhere and probably tough enough to survive a nuclear blast.

Candytuft. The perennial Iberis looks much like the annual--low, dark-green foliage, bright white flowers in spring and early summer.

Thrift. The various Armeria bloom only in spring but then they are covered with pink ball-like flowers on foot-tall stems. The foliage is grassy, grows as low clumps a foot wide.

Penstemon. The border kinds grow 2-3 feet tall and flower spring through fall. Look for them in bloom to be sure of color since they can be deep red, pink or purple.

Physostegia . The plain purple is so strong it can get out of hand, spreading underground (though it is easy to dig out), making mats of low leaves and spikes of purple flowers that are 3-4 feet tall in late summer.

Purple coneflower. Perennial cousins of the gloriosa daisies, these grow 3-4 feet tall, though only half as wide, and carry purple flowers all summer and fall. White Swan is a white-flowered form.

Yarrows. The various Achillea are tough, spreading plants, some only inches tall, others to 3-4 feet. Most are yellow, some purple, rose or white. There are also elegant new pastel colors, named Summer Pastels and Debutante.

Spires for the Garden

These are the church steeples in the village of perennials:

Adenophora . New to California gardens, they are relatives of the campanulas, with similar lilac-blue bells on stems 2 feet tall. They do spread to form colonies of low leaves, but reportedly are not rampant.

Bearded iris. Needing no description, leaves and flowers are strong, vertical accents among other perennials. Bloom now and some again in the fall.

Delphiniums. Though they are true perennials, they are best planted every year (and in different spots in the garden) from quart pots that have not begun to send up spikes. Flower spikes on Giant Pacific types can get to 6 feet, so stake them, though there are shorter kinds that grow to 3-4 feet and don’t need support.

True-blue through purple, pink and white flowers are unbeatable for drama, though these perennials do need regular watering. Bloom in late spring, again in fall if spikes cut to ground.

Gayfeather. The plain old native American species, Liatris spicata is the strongest and brightest. Plume-like spires of pure purple in the fall are 3 feet tall. Make foot-wide, foot-tall clumps of grassy leaves

Peacemakers

Use them between other perennials. Because they have white or green flowers, these help cool off hot summer color schemes, or smooth differences:

Nicotiana . Really green. Vertical growth to 2 1/2 feet and chartreuse flowers distinguish this short-lived perennial that will come back from seed. The green flowers go with any other color.

Shasta daisies. Clean white daisies on plants that can be as tall or as short as you like, bloom in June with agapanthus (a nice mix). Snow Lady is a seed-grown strain only a foot tall. Others can get to 3-4 feet. Some such as ‘Marconi’ have frilly double flowers. All spread and form clumps that are best dug up and replanted every few years.

For Shaded Spots

They will not grow where it is truly dark or dreary, but try these where there is dappled sunlight or bright shade, perhaps mixed in with the ubiquitous impatiens:

Francoa ramosa . Makes clumps of fairly large leaves about 2 feet across. White flowers on graceful 2-3 foot stems in summer.

Rehmannia elata (also sold as R. angulata . Rose-purple foxglove-like flowers on stems 2-3 feet tall, spring through summer. Forms 2-foot clumps in time, spreading underground.

Heuchera Bressingham Hybrids. The seed-grown English strain of coral bells has larger flowers in much brighter colors, from pink through red. Blooms heavily early spring. Likes lots of water, some sun near coast.

Japanese anemones. At this point in the year, they look like 2-foot-tall bouquets of maple leaves, but in the fall, they have much-branched spikes of dainty flowers 4-6 feet tall, in pure white or shades of pink and lilac.

Most perennials go somewhat dormant or completely so in winter and they need to be trimmed up or cut back at that time. Some need to be divided into smaller clumps. In an early autumn column we’ll suggest what to do to each of the perennials listed here.

A Touch of Gray

These add lightness and a Mediterranean look to the garden, looking like pools of sunlight among darker-foliaged perennials:

Dianthus . Low-spreading mats of gray only inches tall, topped with red through pink flowers in spring. A few flower almost all year (‘Penny’ is best at this); others just in spring.

Lamb’s ears Stachys . Quickly spreads to form a soft gray patch 2-3 feet across. After a few years, it begins to die, but ends can be cut off, along with a few roots, and replanted.

Lychnis. Neat, short clumps of gray leaves, to 2 feet across, sprout 2-3 foot stems topped with pink or white, or shocking magenta flowers in spring, early summer.

Snow-in-summer. Cerastium blooms white in summer, has handsome gray foliage all year. Only a few inches tall, it is a ground coverer and spreads several feet.

NURSERIES THAT SPECIALIZE IN PERENNIALS Turk Hessellund Nursery, 1255 Coast Village Road, Santa Barbara, (805) 969-5871.

Sperling Nursery, 24460 Calabasas Road, Calabasas, (818) 340-7639.

Sassafras Nursery, 275 N. Topanga Canyon Blvd., Topanga, (213) 455-1933.

Burkard Nurseries, 690 N. Orange Grove Blvd., Pasadena, (818) 796-4355.

Southern California Nursery, 5526 S. Sepulveda Blvd., Culver City, (213) 390-3547.

Palos Verdes Begonia Farm, 4111 242nd St., Torrance, (213) 378-2228.

Roger’s Gardens, 2301 San Joaquin Hills Road, Corona del Mar, (714) 640-5800.

Judy’s Perennials, 436 Buena Creek Road, San Marcos, open by appointment, (619) 744-4343.

Perennial Adventure, 10548 Anaheim Drive, La Mesa, (619) 466-1203.