shadows with vray sun

I’m working on certain architectural rendering and I am trying to simulate plants around the house and within the house.
Those plants are simple object with green transparency. I like the effect and it is similar to what I wanted, but what is disturbing me, are those heavy shadows. How can I make them less visible?
Material is simple Vray mat with 1.0 refraction and fog color.
Lightening is done only with Vray Sun&Sky.
Can I also achieve similar result also with new Vray fast SSS? Any tip on this?

Check on affect shadows in the materials refraction options.

are the “green things” generating GI?

thanx for the replies, the effect shadows thick did the thing