How to create low res grass?

like they do in some of the games, when there is some grass sticking out. Not the realistic hair particles because they take so much data.

some is done by circular groups of flat planes:
http://www.game-stuff.com/collection/grass_collection_1/19.jpg
other types are done in strips:
http://i.imgur.com/P47fWFz.jpg

how is that done though?

Planes w/alpha textures

Planes arranged in a circle, the grass texture unwrapped onto the planes, and then a transparent node with the alpha mask of the grass plugged into it should do it.

okay, so how many planes would be alright for the alpha texture?

that will depend on the effect you want, and the textures you use. If, for example the grass is far away from the camera, and the camera is not moving too much, 1 plane can be enough. Other situations may require more planes, like in games where you normally walk through the grass, you may need 3 or more planes so you can see it from different angles.