There is a lot of info out there on how/what to plant over a septic drain field. Generally the recommendations are for turf grass (lawn), wildflower seed mixes, ornamental grasses and shallow rooted groundcovers. Some shallow rooted perennials may be appropriate as well, but avoid shrubs or larger woody plants

Here is a link that might be useful: planting over a septic drain field

Yes, stick with herbaceous stuff and grasses, not shrubs. Most any shrub's roots will go 3ft down in sand.