Oct. 4--Here's a gardening challenge: You have a space to plant, in full sun, with exposure to wind, cold and pollution. There's no water. Nothing may grow too tall, but it's physically risky to weed and prune. And above all, it needs to be pretty -- to the dozens of people who see it every day, it symbolizes your neighborhood.

We're talking about the roundabout, and its smaller cousin, the traffic circle. As traffic-calming devices, they've been around Tacoma and surrounding communities since the 1980s, and since then, folks have realized what a challenge they pose to plants.

So if you have a circle that needs fixing, or might be getting one soon, read on.

"Drought-tolerant, low-growing and minimal maintenance," sums up gardening consultant Sue Goetz, on what plants suit roundabouts. "They are some of the worst conditions you could ask of plants -- exposure to exhaust, full sun, no water, traffic."

Yet despite the landscaping issues, roundabouts and traffic circles are popular in this area. The first roundabout in Washington state was built, in fact, in University Place in 1997. Since then, there have been seven more there, plus three in Tacoma, six in Gig

Harbor and two "neighborhood roundabouts" in DuPont, according to the Washington State Department of Transportation.

Traffic circles, which are smaller and don't legally require drivers to slow or yield, are even more popular -- 143 have been built in Tacoma alone since 1989.

"They've been shown to reduce accidents by 62 percent," says Jennifer Kammerzell, associate engineer in the City of Tacoma's traffic section.

And while the city does offer to fill in circles with asphalt or art-filled concrete, many neighborhoods choose to landscape. Residents don't even have to pay for it, with topsoil and minimal groundcover supplied by the city, and funding for the rest coming from Innovative Grants through Neighborhood Councils.

The problem lies in exactly which plants to get, how to set them up and the maintenance.

For traffic circles, visibility is key. Plants need to be less than 3 feet wide and high, says Kammerzell, and the central sign needs to be visible. Small rocks and pebbles are discouraged, as they can roll off and become hazardous. There's no room for really big rocks. And there's no water supplied.

"New Zealand flax, and helianthemum or sun rose," recommends Scott Gruber, co-owner of Calendula Nursery, for medium-size plants. Gruber has designed several local circles, including the one at South I and South Eighth streets, plus the road-closure triangle two blocks up at Sixth Avenue.