My friend Bill is frustrated by his yard's resistance to the bermuda grass lawn he's trying to get established. As my yard is overrun with the stuff, I offered him this simple advice for getting bermuda (or perhaps any spreading grass) to "stick," and I offer it to you for what it's worth:
One must remember, first and foremost, that bermuda operates on a principle of contraries; where you don't want it is where it will thrive.
So toss out your sprigs with as great an air of carelessness as you can muster. If you can find a way to casually drop them along the ground as you run your lawn mower, or better yet the rototiller, the sprigs will think they have been dropped as "volunteers" and may not really be wanted in that spot. Then stand where you most want quick and thorough coverage, and say in a loud voice,
"Gee, this is a great spot for a vegetable garden! I sure hope the bermuda doesn't overtake it!" Actually going through the motions of putting a few vegetables in the ground, for reinforcement purposes, will guarantee the effects of your announcement.
Using this method, the sprigs can be tossed onto the ground and not "set," covered in black plastic for two years... it won't matter; you'll have more bermuda grass than you will know what to do with.
And I'll be glad to send you some sprigs from my vegetable garden to prove my point. Yeah, the grass that survived the two years covered in heavy black plastic.