how often are we advised to cover the ground for a season or two to kill weeds? I have just dug up massive heap of old soil with a large sheet of tin at the bottom. Even after 20 years and under 2 metres depth of earth and metal, the first thing I saw on lifting the tin was a monstrous tangle of vicious white bindweed roots - just getting ready to spring into furious growth. So, covering the ground works maybe, if it is a permanent cover, but as a weedkiller.....well. the jury is still out I think.