How to Prune perennial phlox 'Border Gem'?
Deadhead to promote continous flowering and cut back to the base in late autumn or early winter

perennial phlox 'Border Gem' · Phlox paniculata 'Border Gem'
Will grow well in fertile moist but well-drained soil in full sun or partial shade. Apply fertilizer in Spring to promote growth or a thin layer of compost top dressing to add nutrients to the soil. Pinch back growing tips to promote bushiness.
Deadhead to promote continous flowering and cut back to the base in late autumn or early winter