I have small problem, in older versions of UE4 this option was in material detail panel but now i searched few hours and can’t really find it:/
It is still there. Make sure that you enable Show All Advanced Details or use search field.
http://image.prntscr.com/image/c2f963701f164d16b97c3a72629a81ff.png
Thank you, it was very helpful my grass looks now awesome:p