Lobelia is a nightmare here, I'd even call it invasive. I had some trailing stuff in a hanging basket one year. Ever since, it pops up all over the garden, self seeding into pots and even making it all the way to the veg. It's not supposed to be hardy, but it survives every winter in my front garden and daffodil pots like a green weedy carpet. I gave up pulling it out a long time ago, I just leave it as ground (/pot/bed/paving/brick/car/postman) cover now.
The only thing that beats it back is the willow herb, and the occasional forget-me-not.
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The only thing that beats it back is the willow herb, and the occasional forget-me-not.