Question WHEN IS THE BEST TIME TO PLANT CREEPING PHLOX? Answer Creeping phlox is a tough plant! You can plant it either spring or fall. If you plant it now, you will be able to enjoy it early spring when it flowers. Tags: CareDesignFAQProjects Related Questions Where should I plant my hydrangeas? How do I prune once the flowers turn brown during summer? How do perennials survive in Casa Grande weather? I’ve had my hydrangea for 4 years and no blooms. It looks healthy not sure what I’m doing wrong.