If you spawn grass with the foliage tool, it has a configurated cull distance. This distance decided from which point the grass should be rendered or not.
You can adjust this, the higher the Cull Distance, the further away its rendered. But do know, the more you render, the heavier it gets. Most devs use the trick to have the grass foliage the same color as the grass texture on the landscape.
Combined with larger foliage (rocks, bushes, trees), you dont need a high Cull Distance as the player wont really notice it.