Switchgrass is best planted with a no-till drill.
But if you don't have one. or can't get one.
Frost seeding is a good way to go to. It's best done Late March or early april.
To get a great stand of switchgrass. You will need to Kill all weeds and Grass. That's there now. It's best to spray in the Fall. Then a early spraying again in the spring. If everything is still brown in the spring. you can wait till the Fallowing Spring. You may need to use a Little 2-4-D in the spray mix.
Frost seeding is done while there is frost in the soil. The freezing and thawing action allows the seeds to work themselves into the ground. Switch can be done this way, but you need to spray this fall to kill off existing vegetation. The switch seed also needs the cold temps to become viable, according to some.
Anyway, give it a shot and see what happens. Like I said, it does take some time to fully develop. In that time, weeds and grasses can invade.