I'm no expert beeseejay, but I don't think I'd use the grass, I think it would get ver brown and messy, I try to get some moss to line my baskets, it helps to keep the basket moist, and it's very cheap at the nursery near me, looks more natural than those ready made liners too!................
No, beeseejay, grass would rot quickly and fall out with the compost, coco fibre will last for a couple of seasons and look ok if you plant trailing plants in the basket.