If you want to put plantings on or near your POWTS, you should plant a species of plant that has a herbaceous root system.
You should not plant a species of plant that has a woody root system very close to or on top of the absorption field. The roots from this plant group tend to grow or migrate in the direction of a moisture source. They will work their way into the piping network. Once inside, the roots will begin to clog the piping. Given sufficient time, they will cause a system failure.
The alternative to a woody root plant species could be flowers or wildflower seeding.