Unfortunately there is not an easy solution for this problem:
Individual blades are right for small areas and cutted edges, but not for large areas (because the high number of elements generated), and clumps are fine for large surfaces, but not for clean edges. As you can see in the Forest Pro for lawn
post, there are two options:
a) Adjust the radius of the clump, to get the best balance between size/edges.
b) Combine both elements, using two separate Forest objects or two areas (there are a couple of sample scenes in the post).
Note: there are not problems using option b) on uneven surfaces, but it is necessary to create an extra spline for the falloff. This issue is discussed at the end of the above post.
I know there is a message "Grass Problem with curb" but I don't understand how to do it
Please, tell me what you don't understand exactly (these are advanced techniques, i now).