That's a good question Theun's. I have had some people call my Dio's a vignette, so I am actually a bit confused over it. To me, a Diorama is a scene that shows the model in a natural setting with some form of activity going on around it, whether there is one figure or 100.
I have heard it said that a Vignette has only 2 or 3 figures where as a Dio has more and tells a story. But that could mean that a vignette is only 2 or 3 figures with nothing else.
If I may use a couple of personal examples, to me, these are both Diorama's
There is only 3 figures in each, but hopefully there is a story there.
But, I don't see this as a Dio, simply a model on a base.
That's my take on it anyway.
As for scatter grass, I get mine on line. My LHS doesn't carry much, especially woodland scenic. I like their stuff as there is such a big range and I like to mix it up.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3