Everyone loves butterflies, and plenty of gardeners plant flowers to attract them. But new research shows that not all flowers are equal when it comes to luring butterflies. Even within one kind of flower, butterflies, it turns out, have a preference.

In a study at the University of Kentucky, one heirloom zinnia proved to be a butterfly magnet. Lilliput, a cultivar developed in the 1890s, attracted nearly 20 butterflies, while three other zinnias -- Oklahoma, State Fair and Pinwheel -- got fewer than half that number.

Why would butterflies prefer Lilliput zinnias?

As zinnias go, it's not all that exotic. Lilliput is readily available from seed, easy to grow and known for its prolific flowers. Butterflies are attracted to bright colors such as red and yellow, but these zinnias are a mixture of several colors. So there's only one possible explanation: the nectar Lilliput produces.

Over the years, flower breeders have emphasized specific traits for improving flowering plants, such as the color, size and shape of the flower and the disease resistance and compact form of the plant. But the quantity and quality of flower nectar has never been a consideration. Many breeders have likely sacrificed nectar production for other, showier qualities. That could be why an old-fashioned zinnia outperformed the three newer cultivars.

As gardeners, we tend to want new flowers with desirable traits such as disease resistance. Increasingly, however, more of us are aware that our gardens play a role in the larger environment. We also want plants that feed and shelter butterflies and other nectar-seeking insects.

Plant breeders aren't likely to suddenly make nectar production a top priority. But you can choose plants that look good and do good by butterflies. Instead of selecting cultivars, which may have had some of the nectar bred out of them, put in a few native flowers or species flowers (which haven't been altered by man).

You also can observe your garden and see which flowers not only draw butterflies but actually have butterflies feeding on them. Insects may come close to a flower, but they don't necessarily stay and feed.

Here's an example: In my own garden, I have two kinds of blazing star: Liatrus spicata, a Minnesota native, and Kobold, a popular cultivar prized for its long bloom time and short, stiff flower spikes that don't need staking. I doubt Kobold is a good source of nectar, however, because butterflies don't spend much time on this plant, but I often find them on the species plant, Liatris spicata, as well as other gayfeathers, including Liatris aspera.

If you'd like to make your garden more butterfly-friendly, a Lilliput zinnia isn't your only option, though it's a proven one. Consider planting annuals such as flowering tobacco, impatiens, marigolds, phlox, sunflower and verbena, especially Verbena bonariensis, which often self-seeds. Or try perennials such as aster, bee balm, butterfly weed, chrysanthemum, daisies, purple coneflower, sedum and yarrow.

For more information on butterfly gardening, go to www.extension .umn.edu/distribution/horticulture /DG6711.html.

Mary Hockenberry Meyer is a professor and Extension Horticulturist with the University of Minnesota.