Dof pulling focus

This is a new technique i am trying out for the pulling focus of the depth of field. I have rendered out a clump of moving grass on a seperate layer:



And then I rendered a still of the rest of the scene which already included the depth of field.



After this i composited the two together and started by blurring the background and keeping the grass in the foreground in focus. I then incresed and keyframed a blur on the foreground grass and systematically reduced the blur of the background scene. This is the result: