Coaxing a trumpet vine to bloom

Q: I need to know the name of the plant that spills down the side of the concrete overpasses going south on Interstate 5 underneath the Washington State Convention Center. I have had many visitors dumbfounded by the greenery and the mass of these plants. If these plants can survive limited sun and constant pollution, I have to have one.

A: The green veil draped over I-5 consists of a pair of plants, according to Iain Robertson, professor of landscape architecture at the University of Washington, who has recently redesigned many of the plantings at nearby Freeway Park.

Unfortunately, one of the plants is English ivy (Hedera helix), an invasive plant here that should never be used in our gardens for fear it'll spread and take over parks and natural areas. In your home garden it will swamp and bury the other plants.

Robertson says that while ivy makes up the largest area of "curtains" over the freeway, the plant that hangs down farthest is Parney cotoneaster (Cotoneaster lacteus), a tough groundcover with showy berries beloved by birds.

Q: We have had a "Madame Galen" trumpet vine for a couple of years in a sunny western location and cannot get it to bloom. It is doing well otherwise. Any suggestions would be greatly appreciated.

A: It can take up to five years for a trumpet vine (Campsis radicans) to burst into bloom. It flowers on the new season's wood, but before it matures enough to bloom, it's best not to cut it back too severely in winter. Fertilize it lightly or not at all, for fertilizer tends to promote luxuriant foliage over flower. Be patient with your vine and don't pamper it; it does best in lean conditions. The gorgeous flowers will be worth the wait, for you and the hummingbirds. Remember when you handle this vine that all parts are poisonous.

Q: I inherited three young ginkgo trees grown from seed passed down from the original petrified ginkgo forests near Selah. I know they fare well in Eastern Washington, but am not sure of the spacing, soil conditioning and amount of sunlight they would prefer in Maple Valley. Any suggestions?

A: Ginkgo biloba are among the most ancient plants on earth, and so beautiful, with curious leaves, a handsome rounded shape and pure golden fall color. They have a lightness about them that particularly suits our often-gloomy weather — you can count on ginkgos never to make a dark shadow in the landscape. They're also tough enough to thrive even when planted as urban street trees.

You can be sure that a tree that's survived since the days of the dinosaurs isn't too persnickety about aspect or soil. Ginkgos do well in sun or partial shade, grow in just about any kind of soil and tolerate drought and wetness both, which is ideal for our winter wet/summer dry climate pattern.

Just don't plant your trio of ginkgos in a line, unless you're using them as street trees. They'd look best planted as a little grove, perhaps with a hedge, house or fence as backdrop.

Valerie Easton also writes about Plant Life in Sunday's Pacific Northwest Magazine. Write to her

at P.O. Box 70, Seattle, WA 98111 or e-mail planttalk@seattletimes.com with your questions. Sorry, no personal replies.