Grass and shallow-rooted ornamentals: yes. Trees and large shrubs: never. Roots will infiltrate the tank and pipes. Maintain access to lids and risers; mark them so future landscapers don't damage them.
More detail
Safe choices for over-tank or over-drain-field planting: turf grass (any standard variety), low-growing groundcovers (creeping thyme, sedum), shallow-rooted ornamentals (most annual flowers, herbs, hostas, daylilies), and short ornamental grasses. Avoid: anything woody, anything labeled deep-rooted, vegetable gardens (food safety from incidental effluent contact), and any landscape feature that requires excavation or grade change. Maintain visible access to riser lids; spray-paint the perimeter of the lid annually so seasonal landscaping crews do not bury them or damage them with edgers. If the homeowner wants visual screening of riser lids, decorative covers (artificial rocks, planters that lift off) are available and add $50-$150 per lid. Cincinnati landscape-crew coordination: when hiring landscape services, mark the riser lid perimeter with spray paint annually so seasonal crews do not bury or damage the lids. For septic systems where the homeowner wants visual screening, decorative covers (artificial rocks, planters that lift off) work well at $50-$150 per lid. Avoid permanent landscape features that would require excavation to access the tank. Greater Our Cincinnati technicians frequently encounter homes where prior landscape work buried the tank lids 6-18 inches below grade; bringing risers to surface during the next pump visit costs $200-$400 and saves hours of labor on every subsequent service call.