there is actually a preset in fur for grass (looks pretty nice too)..... but fur as a whole will add quite a bit of time to your render. That, and depending on what scale that thing is, you might have a hard time getting the grass to a realistic thickness. Although there is one nice thing about using fur - you can use maps (like for bump or tansparency maps) for where you want grass, and where you don't (and length, and density, etc...).