Lay down a thick layer of CARDBOARD in your raised garden beds to kill the grass. It is perfectly safe to use and will fully decompose, but not before killing any grass below it. They’ll also provide compost and food for worms. @ Home Improvement Ideas
Recycled railway sleepers stained for a raised garden bed. I'm making a raised organic vegetable bed out of reclaimed (in other words, genuine) sleepers, too - to fit in with the many other sleepers in my garden. But I have been advised that it is best to put a sheet of plastic between the reclaimed sleeper and the soil/compost, because the tar in the sleeper is NOT good for your food plants.