When I did mine I burned it down w gly, mowed it tight, but sprayed atrazine and had the switchgrass seed drilled in may. I went with Kanlow. It came in wonderful and on year 4 now...it is crazy thick and avg 6-7 feet tall. I thought about planting with oats or something else, but all in all, something else is indeed a 'weed' and will compete with the switch. I think the Atrazine is the key....pre-emergent that will keep seeds from even germinating and way less competition.