Q. I have three young Japanese lilac trees and campanula has started growing around the base of two of the trees. How can I get rid of this horrid invasive plant without damaging or killing my trees?
A. Creeping bellflower, Campanula rapunculoides, looks like a nice volunteer plant until you realize what it is – a thug that quickly chokes out other plants. It spreads by its root system as well as seeds. Each plant can produce up to 15,000 seeds, so you can see why it is so successful as an invasive weed.
Bellflower isn’t blooming now, but later in the year, it can be recognized by its stalks of purple bell-shaped, five-lobed flowers. Each is around an inch long, and they grow up one side of the stem. The base of the plant has heart-shaped leaves, connected to the plant with a short stalk, and a purple stem. As you go further up, the stem turns green and the leaves are more lance-shaped and they no longer have a stalk. There is a native campanula that is not invasive that looks similar, but the flowers grow in a clump. There are also lots of campanulas sold in garden centers that are just fine. Campanula rapunculoides was first introduced as a garden plant, but has turned out to be a problem.
Control is tough, and all methods will need to be repeated for several years. Digging out the plants is recommended, but you have to go six inches down to make sure you get everything. The plant has two kinds of roots, lateral rhizomes and vertical roots. You have to get everything out, which is especially hard when digging around other plants. Cutting back the plants as soon as you see them will weaken but probably not stop them. But, it will keep them from re-seeding.
This tenacious weed also resists many herbicides. If you choose to use a chemical, Extension sources recommend glyphosate. Since it is next to your trees and glyphosate doesn’t know the difference between good plants and bad, don't spray it on. Even a slight wind can cause sprays to drift to desirable plants. Instead, use a foam brush to apply it to only the bellflower leaves. Wear protective gloves and follow the directions on the label. As long as you don’t get the glyphosate on your trees, they should be fine.
The master gardeners continue their summer series next week with a program on Gardening with Children. The class will be given during the day and repeated in the evening, 10:30-11:30 a.m. and 6-7 p.m. June 10 at Mt. Royal Library and June 13 at West Duluth Library. Children welcome!
Written by U of M Extension Master Gardeners in St. Louis County. Send your questions to firstname.lastname@example.org.