Found an old foam ball in a Clients' garden the other day, with a whole clump of dog violet growing right the way through it!
... you can see where the foam rubber ball is starting to disintegrate, as well. Yes, I know it looks a bit like a potato, but it's foam, I assure you.
And here is the stem attachment, on the upper surface.
Amazing, isn't it?
And the moral of this story? Errr... plants are amazing, they will grow through anything. Oh, and don't throw your toys away in the garden, put them in the bin.