Campanula rapunculoides: my new most hated plant?

I have posted before about the evils of garlic mustard (Alliaria petiolata, herbe à l'ail), which is devastating forests in the Toronto area, but in our own garden the biggest invader is Campanula rapunculoides (creeping bellflower, or as I call it, creepy bellflower, campanule fausse raiponce).

Although I knew creepy bellflower is invasive in southern Ontario, I hadn't been trying to remove it from our garden because the landlords' son is very fond of it, and it is very pretty (see photo at bottom of post). I thought I would just stop it from spreading by deadheading it. Ha.

Creepy bellflower spreads mainly by roots. It forms a thick mat of roots which make it impossible for anything else to grow. Realizing that creepy bellflower was part of the reason good plants I put in weren't making it, I decided I would try to at least thin it out.

The pile of roots above represents about an hour of hard work. Unlike garlic mustard, which pulls up quickly and easily, creepy bellflower roots break off and stay in the ground when you try to pull them up. Sites recommend digging up at least the top 15 cm of soil and removing all roots. Any bits of root remaining in the ground will regrow.

And here is the depressingly small area I removed those roots from. You can see the heart-shaped leaves of more creepy bellflower poking through the fence. I could just pull off the leaves, but that seems pretty pointless when the massive root system under and beyond the fence is inaccessible to me. I think that my landlords' son doesn't need to worry about not having his creepy bellflowers any time soon.

And here's a picture of creepy bellflower from last July. Yes, it is pretty, but it isn't prettier than the other campanulas. The USDA PLANTS Database lists three campanulas and kin native to Ontario:

• Campanula aparinoides: marsh bellflower (campanule faux-gaillet)
• Campanula rotundifolia: harebell (campanule à feuilles rondes)
• Campanulastrum americanum (formerly Campanula americana) tall bellflower (campanule d'Amérique)