The biggest thing that stands out between your reference and render is variety. There is so much variety of plant species in the reference, but little to none in your render. You need to get to modeling several versions of many of those species to start getting something that looks nearly as good or photorealistic. Your biggest problem is not your material, but your models.
Another (smaller) suggestion I have is to use an add shader for the translucency. You can use a setup like the one below to control the brightness of the translucency (connect a mix shader to the translucent node and nothing else, then run that to an add shader that adds it to the rest of the material...the mix factor on the mix shader will control the amount of translucency). Have you noticed that a leaf with translucency isn't generally any darker on the front side as one that is not translucent? I don't know the physical reason why, (perhaps a good question for physics.se), but it certainly seems to be true at least visually. I first learned this trick by looking at the Grass Essentials marketing material by Andrew Price.
For another example of photo-realistic grass, the Cosmos Laundromat benchmark scene has the Blender Foundation's grass shader which if I recall correctly uses simply a mix shader. They also have much more detail in the texturing than your shader currently has, but I don't know what type or style of grass you are aiming for anyway.
I would reference the Gooseberry project (and Andrew's materials if you have the money). Disclaimer: although "The Grass Essentials" is insanely successful and well-rated, I do not own it myself, so take my recommendation with a grain of salt.
You may find more good reference materials on BlendSwap: