I had great luck with just rinsing well, letting sit in a bowl of water for a day (I couldn't get to planting until the next day), then using a chop stick to make small holes and dropping in a "plug" of hairgrass. I put mine about a 1/4 of an inch away from each other.
I frequently see pictures of hairgrass being planted almost stem by stem. I am sure there is some benefit to that method of which I am unaware, but it would drive me batty.
I have noticed that areas that receive less than very direct light are growing slower and are more prone to diatoms (new tank syndrome).