A stormwater filtration system suitable for treatment of stormwater runoff in a developed environment uses a primary treatment bay that includes a filtration bed with live plant matter. A second treatment bay treats water that exceeds the maximum throughput of the primary bay. A reservoir stores treated runoff to water the plants during dry weather. Removable trays on the surface of the primary filtration bed provide plants suitable for ground cover. Additional bays expand the filtration bed throughput and accommodate extended root systems. A flow control may be provided for the primary treatment bay.