Route Art How To Place Large Amounts Of Foliage Without Lag?

Hi everyone,
I was wondering how I can place large Amounts of Foliage in an area without having major Lag? I have a lot of fields and plants around my Route which I need to represent but how do I do so without having large Lag? But I want the fields to look nice and full and not just spotty plants, is that somehow possible?
Thanks!