What are the FAA regulations on grass airstrips like grass height, lighting, necessary aircraft equipment, and the like?
(a) In a manner authorized by the Administrator, each certificate holder [must] maintain and promptly repair the surface of each gravel, turf, or other unpaved runway, taxiway, or loading ramp and parking area on the airport that is available for air carrier use as follows:
(b) FAA Advisory Circulars contain methods and procedures for the maintenance and configuration of unpaved areas that are acceptable to the Administrator.
So I went looking for those advisory circulars. There are probably more that I haven't found, but AC 150/5300-13A - Airport Design beginning at page 82 seems to have the sort of thing you're looking for.