Any idea for what sss radius should be for things like leaves and blades of grass..Thank you

[madsd]

Usually, those are just single sided. Rarely do you want to use actual geometry unless hero shot. For populating a forest with 100000 trees having 10000 leafs, no practical need to add all that extra geometry. Speed Tree for example, defaults to plane. All popular vegetation plugins for my host also does planes.
So, that makes straight up SSS depth kiiiinda redundant, as Translucency works for that. You tick the use "Thin walled" in the material and use a control map for the SSS color and strength, and it will look pritty good, when straws or leafs are lit randomly from different angles.

Of the straws or leafs has some bending going on, use a falloff control for glancing angles to filter the translucency, forest pack pro shaders use this trick for example, and it looks great and realistic.

[Anonymous]

Problem is that the plugin i use doesn't use planes it creates actual leaf geometry and the material. Name of plugin is forester.

[madsd]

Ok then.
Just dial in radius till it looks plausable, it also depends on the leaf type, and your lights and what you want to end out with in the end - visually speaking.

Add some lamps you stick above and below a single leaf, or a group of leafs and put them into the allround light condition you need and work in with some spots to get a feel. It's very much a feel thing based on the situation.

[Anonymous]

Should i use thin walled and sss at the same time.

[lee_griggs]

Yes, example here.