The genus Phlox encompasses a diverse array of flowering plants, nearly all native to North America, that are highly valued in cultivation for their spectacular, abundant blooms. These perennials and annuals are a popular choice for gardeners seeking a plant that provides extensive color throughout the growing season. The various species in this group are known for their resilience and the ability to thrive in many different environments, from dry, rocky slopes to moist, woodland settings. Their widespread appeal is due to the plant’s ability to produce a massive display of flowers that cover the foliage, bringing a strong visual impact to any landscape.
Distinguishing Features of Phlox Flowers
The most recognizable feature of any Phlox species is the structure of its individual flower, which is classified as salverform. This distinctive shape consists of a long, narrow corolla tube that flares abruptly at the end into five flat, petal-like lobes. The corolla tube is where the nectar is held, making the flower attractive to pollinators with long mouthparts, such as butterflies and hummingbirds.
The five lobes of the flower are typically flat and spread out, creating a pinwheel or star shape, and may sometimes have slightly notched or ruffled edges depending on the species. These individual flowers are small but are massed together into dense, showy flower clusters at the tips of the stems. In taller varieties, these clusters often form a pyramidal or dome-like shape, known as a terminal panicle or cyme. Phlox offers one of the widest color palettes in the garden, ranging from pure white, soft pinks, and deep magentas to vibrant reds, purples, and even true blues. Many cultivated varieties also feature a contrasting “eye,” a small splash of color at the throat of the corolla tube, which enhances the flower’s visual depth.
Leaf Structure and Stem Characteristics
The vegetative parts of the plant, the stems and leaves, provide important clues for identifying Phlox when it is not in bloom. A consistent feature across the genus is the arrangement of the leaves, which grow opposite each other on the stem. The shape of the leaves, however, varies significantly between the tall and low-growing species.
Taller, upright varieties like Garden Phlox feature leaves that are generally lanceolate, meaning they are spear-shaped and relatively broad, reaching several inches in length. These leaves are often thin and may be smooth or have sparse, fine bristles, with prominent lateral veins that curve upward near the margin. Conversely, mat-forming types, such as Moss Phlox, have much smaller, needle-like or awl-shaped foliage that is compressed and thickened, often forming a dense, tufted cushion.
The stems of Phlox plants are typically herbaceous, though they can become semi-woody near the base in older plants. In tall species, the stems are stiff and erect, often presenting with a green or reddish hue, providing the structural support for the heavy flower clusters. Creeping species feature stems that spread horizontally along the ground, rooting where they touch the soil to form a dense mat.
Growth Habit and Plant Size
The overall architecture, or growth habit, of Phlox is the most obvious visual differentiator, neatly dividing the genus into two major categories. The first category is the upright, clumping habit, exemplified by species like Garden Phlox (Phlox paniculata). These plants form dense, vertical clumps that rise significantly above the ground, typically reaching heights of two to four feet. This vertical structure makes them suitable for the middle or back of a traditional garden border, where they add height and a strong point of interest.
The second distinct category is the creeping, mat-forming habit, most famously seen in Moss Phlox (Phlox subulata). These species are low-growing groundcovers that spread widely and horizontally, rarely exceeding six inches in height. This low, dense growth creates a thick carpet of foliage and flowers, making them ideal for rock gardens, draping over retaining walls, or as a form of erosion control on slopes.
Common Species Examples
Observing the traits of specific species helps solidify the visual identification of Phlox.
Garden Phlox (Phlox paniculata)
Garden Phlox is the quintessential upright type, a tall perennial that grows in a clump up to four feet high. It features broad, lance-shaped leaves and is recognizable for its large, dense, pyramidal clusters of summer-blooming flowers. This species is often chosen for its strong, sweet fragrance and its ability to provide color during the mid-to-late summer season.
Moss Phlox (Phlox subulata)
In stark contrast, Moss Phlox is a low-growing, evergreen groundcover that rarely exceeds six inches. Its foliage is thin and needle-like. In early spring, the entire plant is covered in a massive, colorful flush of flowers, creating a dense, low mat. This species thrives in dry, sunny locations and is often used to cascade over rocks or fill in large, open areas.
Creeping Phlox (Phlox stolonifera)
Creeping Phlox is sometimes confused with Moss Phlox but has a different appearance. While it also spreads, it does so more loosely, sending out runners that root as they grow. Its leaves are oval to oblong rather than needle-like, and its flowers are held on short, thin stems that rise six to twelve inches above the foliage. This woodland species is often found in shadier, moister conditions, producing delicate clusters of flowers in mid-to-late spring.