The genus Phlox encompasses nearly 70 species of flowering plants. While most Phlox species are hardy perennials, several varieties are cultivated as annuals. These popular garden plants are known for their dense clusters of flowers, appearing in colors ranging from white to deep purple. Understanding the life cycle of a specific variety is crucial, as the care and longevity of the plant differ significantly.
Annual Phlox: Characteristics and Cycle
Annual Phlox, primarily Phlox drummondii, completes its entire life cycle within a single growing season. This type grows from seed, flowers prolifically, sets new seed, and dies with the first hard frost. They offer an extended blooming period, often flowering continuously from late spring until autumn when spent blooms are removed. Since they do not store energy to survive winter, Annual Phlox must be replanted each year. These plants typically remain shorter and bushier, reaching heights between 6 and 18 inches, and tolerate warmer, drier conditions, making them popular for containers where season-long color is desired.
Perennial Phlox: Major Types and Longevity
Perennial Phlox varieties return year after year, surviving winter by entering dormancy before resuming growth in the spring. This category includes many species, but two types with distinct growth habits are most commonly grown in gardens.
Creeping Phlox
Creeping Phlox (Phlox subulata) forms a dense, mat-like groundcover. This low-growing plant typically reaches 3 to 6 inches in height, but it can spread vigorously up to 2 feet wide, making it useful for erosion control on slopes. Its evergreen or semi-evergreen foliage is covered in colorful blooms for a spectacular display in early spring. This species prefers full sun and well-drained conditions, tolerating dry, sandy, or rocky soils.
Garden Phlox
Garden Phlox (Phlox paniculata) is an upright, clump-forming plant that is a staple of the mid-to-late summer border. This species grows significantly taller, often reaching between 2 and 4 feet in height on stiff, upright stems. It produces large, fragrant clusters of flowers, called panicles, which bloom from July through September, attracting hummingbirds and butterflies. To maintain vigor and prevent overcrowding, clumps should be lifted and divided every two to three years.
Practical Differences in Phlox Care
The differing life cycles of annual and perennial Phlox necessitate distinct approaches to cultivation and maintenance. Annual Phlox should be planted after the last spring frost and require consistent deadheading, which encourages continuous reblooming until the first frost. Perennial Phlox are typically planted in the spring or fall, establishing a permanent root system that requires long-term management. Garden Phlox (P. paniculata) needs good air circulation and should be thinned out, as its dense foliage makes it susceptible to powdery mildew in humid conditions. In late fall or early spring, perennial types should be cut back to the ground to remove dead foliage and reduce disease risk; Creeping Phlox (P. subulata) benefits from a light shearing after flowering to maintain a dense mat.