Volumetric grass? I can honestly say I've never heard of that one before.
Do you mean detail props/sprites? If so that will definitely require using a VBSP file with a custom detail type and even a custom detail sprite sheet if you want to have custom plants and whatnot. However, you don't necessarily have to make it custom. You can always use the stock detailtypes and detail.vbsp and whatnot. But if you want to make custom detail props, look at this:
https://developer.valvesoftware.com/wiki/Detail_propsThat covers everything you need to know. It takes some effort to figure everything out but once you do, it's simple.
If you want to use stock detail props, simply copy the %detailtype line from a VMT file and paste it in to the VMT of the blend texture you want to use in your map. You said you wanted something that looked like red_grass's detail props, so paste this line in to the VMT of your choosing:
"%detailtype" "redgrass"
Don't modify the quotes or anything in that line or it won't work. The redgrass detail type is pretty outdated though. I don't think it even uses sprite shapes (which that VDC guide is mostly about). Sprite shapes are waaaaaay better looking than simple sprite cards that rotate based on the player's position.