To treat low back tightness with physical therapy, start with gentle stretching exercises like pelvic tilts, knee-to-chest stretches, and cat-cow movements to improve flexibility. Strengthen core muscles through exercises like bridges and planks to support the lower back. Incorporate low-impact aerobic exercises, such as walking or swimming, to increase circulation and reduce stiffness. Maintain proper posture and body mechanics during daily activities, and gradually progress to more challenging exercises as flexibility and strength improve.