How to add details such as grass/rocks to terrain?

I've been trying to add small details such as grass and rocks to the terrain in my game in order to make it look a little less empty and more complete, but I've been struggling to find the right approach. In my head, I'm picturing something like the clumps of grass and pebbles in RuneScape:





I'm not sure how clear it is in the screenshots, but these are small 3D objects, not textures

Currently I just place a ton of GameObjects in my scene and mark them as static, which has the look I'm going for, but it decreases my frame rate dramatically, so I'm hesitant to actually use this solution in production

I know that the built-in Unity terrain has the ability to add "grass and other details", but I'd like to use regular old meshes that I make in Blender since I feel like it gives me more flexibility

 

You'll either need to find the asset and modify it so it works for you
look up free rocks environment pieces etc...
or try making the asset from scratch