There are limits to what can be done over septic systems and absorption fields; the area needs to be protected to ensure it continues functioning properly. Septic sites cannot tolerate a lot of traffic or extra watering and fertilization. Woody plantings like trees or shrubs can damage the underground apparatus and vegetable or fruit gardens could be contaminated if placed too close. For these reasons, landscaping the area with native plants is a very appropriate and beautiful way to utilize the space while also protecting it. Purdue Extension has a published a great guide to landscaping over septic systems using native plants.