LAST MONTH I STOOD on an overpass above a busy interstate freeway, straining to hear a couple of horticulturists enthuse about the butterfly garden they were planting. I was in Washington, D.C., on a tour of Smithsonian Institution gardens, and here in a narrow, concrete-laden corridor between the Natural History Museum and an eight-lane highway, these guys were hard at work creating a garden to teach kids about butterflies.

They had made a little boggy area about the size of a saucepan for the butterflies to "puddle" about in, and were busy planting nectar-laden and host plants. Their excitement, what I could hear of it over the roar of the traffic, was touching. However, I couldn't help but think that all the kids who would tour this garden, squeezed into such an inhospitable environment, could enjoy butterflies in their own backyards if their folks would just add a few flowers to the landscape and stop spraying with chemicals.

It really is that easy to have a garden filled with the flutter of this most beautiful of all pollinators. Not only do these fragile insects fascinate, but they are an indicator of the health of a habitat - garden wisely and they will come. Lawns and evergreen shrubs won't do; butterflies prefer brightly colored fragrant flowers, as we do ourselves. Planning a garden for the health and delight of butterflies conveniently feeds the eyes and souls of humans as well.

Butterflies need the sun to warm them enough to fly, which is why they seek open sunny areas and protection from wind. Garden walls, fences, trellises and hedgerows are excellent sources of shelter for creature and person alike. Butterflies provide a good reason to dig a pond or a bog, as they feed in moist areas, often grouping together in a behavior called puddling. It is a wondrous thing to watch a group of butterflies resting on the ground, rhythmically opening and closing their wings like a line of brightly painted bellows.

Most butterflies suck nectar from flowers, and the flowers that suit them best are the old-fashioned single types. Butterflies love asters, bleeding heart, delphinium, coneflower, wallflower, lupine, beebalm, catmint and verbena. Many of these flowers attract moths and hummingbirds as well. And it is good to leave a patch of tall weeds somewhere about, as butterflies use dandelions and other familiar weeds for food and protection. This is a perfect excuse for messiness: It is all part of your habitat garden.

You can attract butterflies with bright, sweet flowers, but to get them to take up residence, you'll need plants to support every phase of their life cycle. Before they metamorphose into beauties, butterflies are caterpillars, which feed on plants. In his excellent book, "Landscaping for Wildlife in the Pacific Northwest" (University of Washington Press, 1999), wildlife biologist Russell Link discusses food and nectar sources for the caterpillar and adult of each species of Northwest butterfly. If you long to see the dramatic black and yellow Anise Swallowtail flitting about, you'll need to plant fennel and dill as host plants for its caterpillar phase, and penstemon, mint, zinnia or lantana to feed the butterfly.

Always remember that chemicals in the garden destroy the beneficial insects as surely as whatever you are targeting. Even Bt (Bacillis thuringiensis), which is touted as more benign than other pesticides, kills caterpillars, thus destroying future butterflies. What is tolerating some wildness, putting up with a little leaf damage, in comparison with the joy of watching swallowtails, elfins, hairstreaks, coppers and red admirals puddling, flitting, sipping and basking in your garden?

If you'd like to learn more, the Washington Butterfly Association has monthly meetings and field trips; for information, call Idie, WBA president, at 206-364-4935, or visit the butterfly exhibits at the Woodland Park Zoo or the Pacific Science Center.

Valerie Easton is a horticultural librarian and writes about plants and gardens for Pacific Northwest magazine. Her e-mail address is vjeaston@aol.com Susan Jouflas is a Seattle Times news artist.

Now In Bloom: Deutzias are deciduous shrubs covered in pure white flowers in late spring, as decked out and shimmery as June brides. D. crenata var. nakaina `Nikko' is small enough to use as a ground cover, with white star-shaped flowers; D. scabra arches to 10 feet with honey-scented single flowers.<>