Krispy Kreme (of all companies) created a similar kind of sandal as part of a promotion a few years ago, but Kusa's grass flip flops have two distinct differences. They're made with artificial turf, and you can actually buy them.
While it very much looks like real grass, the thick layer of green stuff on Kusa's sandals is actually a synthetic material known as Syn-Turf. It not only looks the part, but I bet it feels pretty similar to the real thing, without leaving grass stains on the bottom of your feet.
The material does need to be fluffed from time to time, but that's far easier maintenance than weeding, mowing, and fertilizing. And the sandals are available now in small, medium, and large sizes for about £20. [Kusa Shoes via Design Milk]