Posted: 22/08/2016 at 14:38
first you just have to be sure that they are dead, things like docks,nettles and bindweed have a nasty habit of surviving the first dose of weed killer.
I would get a gas powered weed wand wait for a dry day and burn off anything above ground level and wait a couple of week to see if anything regrows. if it does give it another dose or try getting the roots out manually.
the area that you want as a meadow I would take off the top 1-2 inches of soil (it will be full of weed seeds) and turn over the soil below. then give it water and wait a week, any weed seeds that are there will germinate you can then hoe the area over and sow the meadow seeds from late September till early October