Well... till if you must, but be prepared for the weeds with Plateau. Whatever you treat with for weeds, be sure it won't also kill your new buffalo grass. Most targeted herbicides will include prairie grasses since that market isn't yet large enough to make preserving them cost effective for the big chemical companies. Plateau is the only one specifically concocted to advance prairie grasses. There are a couple of others you could use but they don't work quite as well.
Wow, I bet buffalo grass plugs ARE expensive. The seed is dear enough! Also, it wouldn't seem to be all that hard to get the seed at the right depth, especially if you're going to till anyhow. You could just till, seed and roll as usual. But if you seed, don't use any mulch since prairie grasses need light to germinate. That's why weed control is such an issue -- weeds grow faster and shade out new grass.
Is your customer going with buff because of its drought resistance or because it wouldn't have to be mowed much?
