The Weedy Bellflower

By Larry Hodgson

I’ve grown all sorts of bellflowers (Campanula spp.) over my lifetime as a gardener, from short, creeping or clump-forming border and rock garden plants like Serbian bellflower (C. poscharskyana), Carpathian bellflower (C. carpatica) and Dalmatian bellflower (C. portenschlagiana) to middle-of-the-garden types like clustered bellflower (C. glomerata) and Viking bellflower (C. ‘Viking’) to tall background varieties like milky bellflower (C. lactiflora) and great bellflower (C. latifolia). Most are perennials, but some are biennials, like Canterbury bells or cup and saucer bellflower (C. medium). And most are easy to control, although a few do have rampant rhizomes that need to be kept in check, like spotted bellflower (C. punctata). 

Only one is a true weed, though: creeping bellflower (C. rapunculoides). And, like any true weed, you probably didn’t plant it: it likely showed up all on its own. 

A lot of gardeners are pleased to see it at first: after all, creeping bellflower produces lovely stalks of dangling blue-violet bells: What’s not to like about that? But you soon find it spreads like crazy, sometimes through seed, but mostly through creeping underground rhizomes, choking out your other garden plants. And it doesn’t bloom all that densely, either. You find yourself with a carpet of creeping youngsters with only a few mature, flowering plants spotted here and there. 

Creeping bellflower, it would appear, is hellbent on taking over the entire world!

History

Creeping bellflower is native to temperate regions of Europe and Western Asia. It was introduced to North America in colonial times, either as a garden ornamental or a vegetable (the tuberous root is edible, as are the flowers and young shoots and leaves, and have a long history of use as a famine food). It has since escaped and become well established throughout Canada and all but the southernmost parts of the USA. It has also invaded New Zealand, Japan and parts of South America, Africa and Australia. In many areas, it’s considered a noxious weed and growing it may be illegal. 

Recognizing the Culprit

That’s a problem! There are several bellflowers and bellflower relatives (like Adenophora spp.) that look a lot like it. So, here are the details:

• It usually reaches about 12 to 30 inches (30 to 100 cm) in height, although can occasionally be taller.

• The stem is upright or leaning. It bears rough hairs and is often purplish, especially at the base.

• The basal leaves are large, triangular, coarsely toothed and heart-shaped at the top with a rough, hairy texture and a fairly long petiole. The largest leaves are about 4 ½ inches long and 2 inches wide (12 cm × 5 cm). As they grow up the stem, they become smaller and narrower. The uppermost leaves have only a short petiole or none at all. 

• Flowers are borne from June to September (in the Northern Hemisphere) on one side of the stem only. They’re blue-violet and about 1 to 1 ½ inches (2 to 4 cm) long, drooping and bell-shaped. They have with 5 pointed lobes, often with sparsely hairy edges.

• The rounded seed capsule has pores at the base that open at maturity so the seeds can be shaken free by the wind. Each plant can produce up to 15,000 seeds per year.

• The clincher in terms of identification comes from pulling on the plant. Other bellflowers readily gave way and are easy to remove. Creeping bellflower will likely resist attempts to remove it. If you do get it out, it tend to tear off at the base and only a few of the upper roots and rhizomes follow. The carrotlike white tubers are found deeper in the ground, about 6 inches (15 cm) down, and have to be dug out. If not, they’ll soon produce a replacement plant. 

(Do note that the tubers are not found directly under the mother plant as you would think, but appear here and there on creeping rhizomes, up to 1 foot/30 cm or more away.)

Controlling a Garden Thug

There is no easy solution to getting rid of creeping bellflower. Here are some thoughts on its control.

• Eat it. I find the tubers and roots have a rather insipid parsniplike flavor. The taste is best in the spring. If you can convince yourself it is a delicious, desirable vegetable (or find a neighbor seriously into foraging), you might just be persistent enough to keep creeping bellflower under control.
• Cover the invaded section of the garden in black tarp and leave it there for two full seasons. Lack of light for so long will kill almost all creeping bellflower plants, but sometimes a tuber remains alive and a new sprout appears. If so, remove it immediately while it’s still weak.
• If you try pulling the plant (indeed, if you are able to!), you’ll discover that will only slow it down. It will soon sprout anew from rhizomes and tubers left in the soil. 
• Try to dig up the entire plant, and that can mean going down 8 inches (20 cm) or more. When you find a horizontal rhizome, pull it up gently and follow its horizontal path until you come to a point where it clings tenaciously to the soil. Dig there, as that’s where it has produced a hidden tuber. It may be wise to sift the soil to remove any remaining fleshy root pieces the plant could resprout from. 

Helpful Hint: The only part of creeping bellflower you should put in the compost pile is its leaves: roots, tubers and seeds can survive composting and come back to haunt you. 

• Never let creeping bellflower go to seed. Sure, you can enjoy the flowers while they’re there, but as the plant reaches the last flower or two, pull it out or at least cut off the flower stalk. 
• Mulch the garden. This won’t get rid of plants already present, but it will prevent new plants from germinating from any seeds that fall.
• Poison it. And by that, I do mean using a systemic herbicide like glyphosate, one that penetrates the plant and disrupts its hormonal circulation. Contact herbicides, the ones that stay on the outside of plant and aren’t absorbed by it—and organic herbicides are of that category—, won’t make much headway against this pest: it will just produce new leaves to replace those lost. I must admit I don’t use systemic herbicides, but if you do, minimize environmental damage by painting it onto the leaves rather than spraying. You’ll find even a systemic herbicide will require repeat treatments.
• Changing the growing conditions will be of little help in controlling creeping bellflower. After all, it will grow in just about any kind of soil—dry or moist, acid or alkaline, rich or poor, dense or light—and most light conditions, from full sun to moderate shade. Deep shade will eventually kill it, though, so you could plant a forest and that will eventually shade the plant out.

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Creeping bellflower: I hope you don’t have this plant in your garden, but if you do and want to control it, you’ll have to expect to put in quite a bit of effort!