Phlox is a genus of flowering plants beloved by gardeners for its vibrant, clustered blooms, but the plant maintains distinct visual characteristics long after the flowers fade. Ranging from low-growing groundcovers to tall, upright garden specimens, these plants possess specific structural and leaf details that allow for identification when only foliage is present. Recognizing Phlox in its vegetative state is important for garden planning and maintenance. This guide focuses on the architecture, leaves, and stems of the non-flowering plant, distinguishing the various types across the seasons.
Growth Habits and Structure
The overall form of a Phlox plant provides the first major clue for identification when flowers are absent. The genus is primarily divided into two architectural groups: upright and creeping. Upright types, such as Summer Phlox (P. paniculata), are clump-forming perennials that develop robust, vertical structures ranging from two to four feet in height. These plants maintain a relatively narrow, bushy profile, spreading slowly outward from a central crown.
In contrast, Creeping Phlox (P. subulata) and related species exhibit a low, spreading, mat-forming habit. These plants typically remain only four to six inches tall but can spread up to two or three feet wide, creating a dense carpet of foliage.
Foliage Identification
The leaves are the most reliable feature for identifying Phlox when flowers are not visible. Across the genus, the leaves are simple and arranged oppositely along the stem, though the exact shape varies significantly between species. Upright Garden Phlox (P. paniculata) possesses deep green leaves that are lanceolate to elliptic in shape, usually measuring four to six inches long. A distinguishing characteristic is the presence of conspicuous veins that branch off the center vein and curve toward the leaf tip.
The foliage of Creeping Phlox (P. subulata) is markedly different, consisting of small, narrow, and needle-like leaves, often only half an inch to one inch in length. These leaves are densely packed along the stems, giving the plant a somewhat prickly or moss-like texture. This foliage is evergreen or semi-evergreen, retaining its structure and color throughout the year. Woodland Phlox (P. divaricata) presents another variation, with opposite, lance-shaped to elliptic leaves up to two inches long on non-flowering shoots, often with a slightly hairy and sticky texture.
Stem and Root System Clues
Examining the stem and root system provides structural clues that confirm the identity of the non-blooming plant. Upright Phlox species, like P. paniculata, are characterized by stiff, erect stems that can reach substantial heights. These stems are often smooth, sometimes developing a reddish or purplish tinge as they mature. They are herbaceous, lacking woody tissue, and typically grow in dense clumps from a robust root crown.
Creeping Phlox (P. subulata), conversely, has low-growing, sturdy stems that spread along the ground. These stems root easily at the nodes where they touch the soil, which is a key mechanism for their mat-forming spread. Woodland Phlox (P. divaricata) further differentiates itself by producing stolons, specialized horizontal stems that creep along the surface and develop into new shoots. The presence of these runners and subsequent rooting at nodes are definitive identification features for the low-growing Phlox.
Seasonal Appearance Changes
The appearance of Phlox in its non-blooming state shifts significantly throughout the year, marking the stages of its annual cycle. In early spring, upright Phlox emerges from dormancy as new shoots often tinged with red or purple before expanding into mature green foliage. By mid-summer, the plant is in its full vegetative state, characterized by its dense clump of upright stems and large, lance-shaped leaves.
As temperatures drop in the fall, the deciduous upright Phlox species begin senescence, with the stems and foliage dying back to the ground. This contrasts sharply with the low-growing varieties, which are semi-evergreen. Creeping Phlox retains its small, needle-like foliage through the winter, continuing to form a green groundcover. The persistent foliage ensures that the plant remains identifiable even during the dormant period.