Yes. Use the Grass Tool which comes with UE4:
They use Hierarchical Instanced Level of Detail (HLOD) for the grass foliage. If you’re using a custom static mesh for grass, make sure that you have 3-4 levels of detail.
You can also take advantage of the HLOD by using the foliage tool. You can paint thousands of trees without any problems – if you do it right.
Make sure you disable shadows. Make sure your trees have multiple LOD’s. If you’re creating the assets yourself, keep a very close eye on the translucent cards used for leaves. Every card adds overdraw, which can start to add up with lots of layers. Sometimes, it may be more performance efficient to just draw more triangles if it means less overdraw.
I have lots of foliage in my VR game and I hit 90 FPS just about everywhere. Using a Vive with a GTX 970.
Use the performance analyser which comes with the engine and tune your scenes to hit 10.0ms. It won’t be easy, but you need to do it. Using this tool with every modification to a scene should become a part of your workflow. Build, test perf, modify, run.