Blue is the color most pursued by gardeners. Yet blue is a mysterious hue with as many personalities as uses. Blue flowers can be tranquil or melancholy, dark as denim or light as the sky, restful as twilight or restless as the sea. They blur boundaries, suggest distant horizons and make gardens look larger.

But above all, blue flowers are sought-after.

"Blue is always the most popular color because it goes with everything," theorizes garden store owner Kathy Tracey. "And because it seems hard to find."

Nursery owner Brian McGowan says blue is the most requested flower color at his nursery. He is puzzled by this. "Is it psychological? It's amazing. Almost everybody loves blue. It must be human nature. Blue, that's the thing people die for. I don't know why."

Let us, then, try to deconstruct the mystery of blue in the garden.

Blue words

Everyone loves blue, but not everyone can agree on which blue (( they love or what to call it.

It can give linguists the blues.

Many languages don't even have a special word for blue, lumping it in with the word for green. The Japanese language only relatively recently developed a distinctive word for blue. In ancient Chinese poetry, the same character was used to describe the color of grass and sky. In Homer's "Odyssey," the blue Aegean Sea is referred to as green.

In his book "The Primary Colours," Alexander Theroux says that names for colors always enter languages in the same order, beginning with black and white, then red, then green and yellow. Blue comes next, but until it gets its own word, it's considered a green.

Today English has many words to describe shades of blue, but confusion persists. By true blue, do we mean saturated cornflower or gentian blue, or pastel sky blue, or the grayer forget-me-not blue, the steel blue of amsonia, or the darker ink and sapphire blues?

And to make it really confusing, most so-called blue garden flowers have purple in them, from just a hint in chicory to quite a bit in catnip. This lack of a clear divide to the naked eye between blue and purple drives gardeners and nurserymen crazy.

"Everybody's always looking for true blue, whatever that is," said McGowan, owner of the appropriately named Blue Meadow Farm, which sells unusual annuals and perennials. "They grill you up and down to make sure it's really blue. They'll complain if something has too much purple. People do get really picky about colors. And often just blue isn't good enough. They want sky blue, cobalt blue, clear blue. They try to come up with names for what they want. There's lots of blue flowers, but finding a particular person's blue, the blue they want, is hard."

Blue roses

The blue rose has been the Holy Grail of plant breeding for generations. After all, according to market researchers, blue is the world's favorite color and roses are its favorite flower, so a blue rose should take flower lovers by storm.

The only problem is that it doesn't exist, even after rose companies poured millions of dollars into hybridizing efforts before giving up in disgust in the 1960s. The closest they could come to true blue was sickly mauve.

You see, the rose family has no members with blue pigment to use as a starting point for breeding. And the gene for blue is like charisma. Either you've got it or you don't.

The petunia and delphinium families are loaded with it, for instance, while the tulip, dahlia, and rose families aren't. And there's nothing hybridizers can do about it.

End of story? Not these days. Biogeneticists have gotten into the act. We'll just borrow the blue gene from a petunia, they said 10 years ago, and we'll have blue roses by 1997.

Obviously, they missed their deadline.

What went wrong? Florigene of Australia did actually succeed in isolating the blue gene in petunias along with the gene that switches it on. And they did transfer this into roses. It was quite a scientific achievement.

Except that the roses with the blue gene still don't look blue.

The problem now is that the pH, or acidity, in the rose organs that carry petal color are all wrong, so the blue is in there but we can't see it. And you can't change the pH without making the whole plant sick.

Florigene has spent millions of dollars over a decade to reach this roadblock, and prospects for getting past it are not great.

But they have had some success splicing blue genes into chrysanthemums and carnations. Blue-engineered carnations are currently on the market in Japan and will eventually turn up here.

Keith Zary, vice president for research at rose giant Jackson & Perkins, has seen the new blue carnation. "It looks lavender-blue," he reports. "It's not very exciting."

If nothing else, the whole enterprise illustrates why true-blue flowers are so rare. We can clone mice and sheep, but blue flowers are still holding onto their secrets.

Blue color theory

Blue is one of the cool colors of the spectrum. The others are green and violet. Blue appears warmer as it approaches the green and yellow range of the spectrum and cooler as it nears violet and red. It's helpful to think of warm blues (turquoise) and cool blues (violet).

All other colors can similarly be divided between warm and cool. There are warm pinks that move toward yellow (peach) and cool pinks that move toward violet (mauve). And it can look awful if you plant flowers in warm hues next to flowers in cool hues of the same color family, like combining cool pink phlox with warm pink carnations.

This is not a big problem with blues, however, since almost all of them are on the violet-red (cool) side of the divide. Very few blue flowers come in warm shades. The turquoise subtropical milkweed oxypetalum is one, and it is difficult to combine harmoniously with other flowers.

But the vast majority of blues combine easily with mauves, violets, and all the many purple-blue flowers, creating a large group of flowers to use for the cool garden.

Variety works

Blue flowers look good with all other flowers. Except blue flowers. Experts agree that blue flowers alone together in a monochromatic garden are a downer.

"I have yet to see a successful all-blue border," says Pamela Harper, who has professionally photographed hundreds of gardens. "Blue flowers bring out the best in other colors, but they don't bring out the best in each other. Blue never looks bad. But it isn't strong enough to have sufficient impact on it's own. It's a better backup color. And if some of the blues are just a tiny bit off, they don't meld."

Yet blue, like white, can be a "snob color" and there was a bit of a vogue in all-blue gardens among the super-rich during the Belle Epoque.

That prompted Edwardian British garden designer Gertrude +V Jekyll to scold: "It is a curious thing that people will sometimes spoil some garden project for the sake of a word. For instance a blue garden, for beauty's sake, may be hungering for a group of white lilies, or something of palest lemon-yellow, but is not allowed to have it because it is called the blue garden, and there must be no other flowers. ... Any experienced colorist knows that the blues will be more telling - more purely blue - by the juxtaposition of rightly placed complementary color."

Yellow and blue was artist Claude Monet's favorite color combination, and garden designer Jekyll, an artist too, also favored touches of yellow to make blues look bluer. The entryway to one predominantly blue garden she designed was dominated by gold foliage.

Though most experts advise against attempting an all-blue garden, gifted Irish colorist Helen Dillon has found a satisfying way to do it.

In her book "Garden Artistry," Dillon writes of cheerfully mixing "a glorious muddle of different blues, never minding whether they are turquoise, sapphire, or lapis lazuli. Purists will say that you shouldn't mix pure blues with mauve- or violet-blue, but the loveliest effects can be made by breaking the rules."

The stars in Dillon's celebrated "blue garden" in Dublin are delphiniums, monkshoods, Aster x frikartii 'Monch,' and Aster thomsonii 'Nanus.' They are accompanied by an ever-changing supporting cast of self-sowing annual blue love-in-a-mist and larkspur, and annual indigo spires and patens and uliginosa salvias. Blue perennial supporting players include catnip, stokesia, echinopsis, campanulas, violas and eryngiums.

But there are also a lot of mauve and white flowers in this blue garden for accent, including penstemons, agapanthus, gypsophila, cow parsley and goat's rue. Towering teasels and other gray foliage plants also tone down differences between the various shades of blue.

A gardener who tries to use only true-blue flowers is walking a narrow tightrope. One plant in the wrong shade of blue can injure the whole brittle picture. But Dillon's technique of incorporating a broad range of blues shading into purple is safer and easier.

Harper has taken a similar approach. "I would not attempt a blue border," she said. But she does combine gray, purple, and white with blue. "I love that combination. It's interesting but not loud, jTC and it gives me an enormous range of plants."

Harper's Virginia garden includes the colored foliage of eupatorium Chocolate, purple smoke bush, cutleaf maples, purple barberries and annual perilla. The flowers, mainly blue and white, include asters, Campanula latifolia, amsonia (an underappreciated favorite and a great second fiddle), Siberian iris and catnip, of which she says, "It's not an exciting blue, but it's very long blooming and has gray-green leaves."

Pub Date: 9/13/98