1. Using scatter tool

Select the grass model you need in assets library, set the radius parameter of the Brush tool to the maximum, the scatter tool is activated and grass will filled inside the selected face.

2. Using grass material template

Select the material where the grass is located, switch the material template to Terrain Grass, the surface of the material will generate model grass. The material parameters allow you to adjust the height,roughness, specular and normal of the grass.

Depending on the area of the material, there may be some delay in the generation.

The grasses generated in the above two ways will import a large number of model faces and are not recommended for large areas. It is recommended to use terrain grass for distant views, which takes up relatively less resources. For close-up grasses, you can use models.