[Don't mind Jamie as he threadjacks here, but watching this means he's gone and gotten himself an idea, and he's going to throw it out to see if it's feasible.]

Does it have to be just roots? Ye can shape those however ye like if you're strong enough, right?

[At least that's the impression he'd gotten out of it, but he's not actually a growth user, so feel free to correct him.]

What if ye brought something else into it that'd help weaken it from the inside? Salt or small bits of metal wrapped up in something that could also be set on fire? If it got hot enough to explode...