There are advantages to using plants over the drainfield. Plants do help provide oxygen exchange and contribute to evaporation necessary in the drainfield area. Choose plants with shallow, non-invasive roots. You don't want breakage or damage in pipes from root intrusions. Grasses are most commonly recommended for the septic area.
Lawn can be attractive.
Don't overload the system by watering it a lot. Very tall grasses like Stipa gigantea aren't appropriate. Edible crops aren't suggested. Vegetable gardening requiresfrequent cultivation and digging in the drainfield area is inadvisable. Any root vegetables planted in this area may be directly exposed to septic tank effluent.