When I open Landscape grass type nothing shows up its just blank
(Yes I know this thread is old, but I had this problem in 4.19 and solved it.)
If you open a Landscape Grass Type and the screen is blank, click Window -> Details, and Grass Varieties should appear.
Edit: Answered on an even older thread: https://answers.unrealengine.com/questions/244583/48-landscape-grass-type-asset-bug.html
You'll need to create a landscape grass type outside of the material editor to assign to the grass node. Also you should type "grass" exactly as you have with the layers, I'm pretty sure it's case sensitive.
Epic have a step by step on setting up the landscape grass in materials
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