that I put my "discovery" here.
Spring is coming and many of you will start to cut the grass in your gardens, backyards etc.
So, do not throw it away. Leave it on some warm and sunny place to dry. After that grind
it (kitchen coffee beans grinder would do fine) and you got simple and very cheap cover
for your diorama. It is a bit dark but still green (especially good for autumn diorama).
On picture you can see dry and grinded grass. Grass is from Summer 2011 and picture is
taken today. So it keeps green color for a long time.
[I hope this would help to someone.
Moderator
I will use this tutorial in the near future 
thanks for the tip