At least 50 cultivars of garden phlox, Phlox paniculata L., are available. These cultivars have been chosen for retail because of variation of flower and leaf color, as well as their resistance to disease.
A perennial, garden phlox is considered a medium flowering plant, and should be placed in an area where it will not hide smaller plants as it grows.
Garden phlox is available in a variety of colors. Phlox bloom in white, purple, orange, blue, lavender, red, peach, pink and variegated shades for about 18 weeks.
Phlox plants usually grow to about 40 inches tall and about 23 inches wide. While cultivars with variegated leaves are available, phlox leaves are usually medium green. The flower dome of the phlox consists of 20 to 40 individual flowers, each about 2 inches in diameter. The flowers have 5 petals that are attached to a long tube.
Growing Garden Phlox
Garden phlox will tolerate shade, but plant them in the full sun for best results. Chose a spot where the fertile soil is moist but well drained. Phlox are heavy feeders, so incorporate organic material into the growing medium. Garden phlox can reseed in the garden, so removing spent blooms is important to keeping phlox contained to a specific area.
The flowering heads of a thriving garden phlox plant may become too heavy for the plant. Stake the plant to help keep it erect.
Dividing Garden Phlox
Good air circulation and proper nutrients are important conditions to keep the garden phlox thriving year after year. To maintain the best growing conditions, divide the plants every 3 or 4 years, more often if they become overcrowded. The clumps can be replanted in a sunny empty place in the garden. The best time to divide the plants is before the new growth starts in the spring. The added bonus of plant division is that better circulation will lessen the chance of fungal problems.
Phlox and Powdery Mildew
Powdery mildew disease can infect garden phlox in the spring and fall when the temperatures are low. While powdery mildew usually doesn't kill phlox, but the plant can become weak and produce deformed flowers.
Caused by Erysiphe cichoracearum L., the fungal problem infects new growth of the garden phlox. Look for a white powdery mass on the surface of leaves and stems.
Shear off half of the flowering head of the garden phlox when the blooms start to fade. This will encourage bushy plant growth.