I was just looking through some older pics and found this one I took of my daughter:
Canon 1Ds mkII, 70-200mm F4 IS L @121mm, f4, 1/250th, ISO200
Now tell me you could achieve this effect in post. It's impossible, unless you were able to mask every blade of grass to define their depth... and even then there are some which are not straight and have varying focus along their length. You can't just do it with a simple gradient since for blade X there's multiple blades in front of and behind it in the same (2D) region of the image which have different blur...