How to add grass and move objects?

Start with a picture of just grass in the format you want.

Then place the existing picture(as a smart object) and mask one of the objects and move it into position.

Next Duplicate the Smart Object, clear the mask on the duplicate and make a new mask of the second object

Repeat until you have all objects in position

Put all the smart objects into a group and either paint a shadow or just add a drop shadow (painting will be more accurate)

Of course, given that there are no elements that would look incorrect at 90 degrees (such as text) you could just turn the whole image on its side.

Dave