Move the black flower a little down, so that the edges are visible.
Apply blur to this black flower.
Filter> Blur > Guassian Blur. Set the value according your requrements. It can vary with the size of your object/image
After applying the Guassian Blur.
The shadow we have created is just too soft, to roughen it up I will apply a Film Grain filter, do this by going to the
Filter > Artistic > Film Grain…
Next set the opacity to 74% or so,
this will give some transparency in the shadow.