I am trying to make an open world game with a big-massive landscape and i am using the grass tool to add grass, flowers, rocks and trees. Thing is that, i need the trees and rocks to have collision without removing them from the grass tool and adding them manually or paint them with the foliage tool. What can i do?
Click on the [Show Instance] tab for the component you want to have collision - at the bottom you can set the collision type.
can you please assist with a screenshot?(we are talking about the grass tool right?)
The foliage tool –
Drop the various grasses, rocks, etc you want into it.
Click the arrow for “Select”
And scroll down.
You’ll find collision options.
This is nice and all,thanks, but i already know that 
Because im making an massive open world foliage is too hard to handle, even with a large covering area and collision. Guys at Epic should make an update about this.
Did you figure out how to do this? I’m also producing a large scale terrain, and I’ve looked at using the Procedural Foliage Tool in order to place foliage such as trees and rocks, and I use the grass tool in connection to the landscape material layers. The issue with using procedural foliage tool for placing rocks, is that the rocks are placed in seeds, groups, etcetera, which isn’t quite what I’m looking for. Having the rocks spawn at for example my rock layer, through the grass tool, it would improve the realism of the world. 
hey, further research has shown that untill now, grass tool doesn’t have any collision just yet. But, if the material you’re using has also rock textures and nodes, then you can just create a new landscape grass type and add rocks to that, and assigning it to the material. Await for Screenshots.