I'm planning to expand my vegetable garden next spring, and want to kill of the weeds in the new area. I also have some rouge cannas there that are firmly resisting my efforts to remove them. I dimly remember something about spraying the weeds and then covering the area with black plastic for a while to kill the weeds. Is this the right thing to do? The intended garden will be a raised bed filled with topsoil and compost. I've also posted this over in the Soil forum.