I did a patch this year, using cardboard from boxes in which carpet tiles were delivered. The source I used said it wasn't necessary to dig up weeds first, but I doubted this, so I did, and then buried them. Creeping buttercup survives this. I used compost from my bin, uncomposted kitchen waste, and spent compost from last year's potato bags, topped off with bought topsoil, and planted runner bean and pea seeds. Some of the seeds disappeared soon after germination, due to the gastropod infestation we have all suffered from this year. So I can't really report back properly.