Phlox are low-maintenance, vigorously spreading and multiplying plants that bloom in fragrant, star-shaped flowers. The many different types of phlox plants are typically divided into two major categories. Creeping phlox is low-growing and blooms during spring, while tall phlox blooms during summer and can grow 2 to 3 feet tall or more. Phlox in both categories produce a range of flower colors, from white to pink to deep purple. Depending on the variety, phlox can thrive in full sun to shady areas. All phlox are sensitive to over-watering and waterlogged soils, preferring moist but well-draining locations.
Water your phlox deeply to soak the soil down to and around the roots once each week during summer when rainfall is less than 1 inch. Water the soil and avoid wetting the flowers or foliage to prevent fungal diseases.
Spread a 1-inch-thick layer of organic compost on the ground around the phlox once each year in spring. On top of the compost, spread a 2-inch-thick layer of mulch to control weeds and regulate soil moisture. Apply the mulch in early summer, after the soil has warmed.
Cut the old flower stalks back on the phlox to promote re-blooming after the flowers fade. If you are growing tall phlox, maintain just five or six flowering stems per plant to promote healthy blooming, removing all the other stems after they reach about 6 inches tall.
Cut the stems on your tall phlox back to about 1 or 2 inches above the ground level after the first hard, killing frost in fall or early winter.
Divide your tall phlox plants once every two or three years to thin out over-crowded plant clumps. Carefully dig up the phlox clumps, separate the healthy roots and replant the phlox at the same depth as they were planted previously.