Keep them in rubbishy soil. I grew mine to cover a spoil heap of rubble, earth and cat poo. They covered it alright, that and the rest of the garden!! They still grow out of it now, regardless of me pulling the wretched things up.

The better the soil, the more leaves you get. The poorer the soil the more the plant thinks 'have to propagate to survive' and produces more flowers.

Personally I've always liked them, but they can get a bit overpowering.

If you want to get rid of them, grow them as a salad plant. They'll all sink without trace!

LTS