Each year, as we reach the peak of summer and head into the fall season, the H.O. Smith Botanic Gardens are bursting with vibrant color. One prominent contributor to this abundance is phlox (Phlox spp.). While the majority of the phlox collection can be seen July through October, there are also spring blooming species showing off as early as April in the gardens. With eye-catching pink, purple, white, and reddish blooms, these plants are loved by pollinators and gardeners alike.
As a genus, Phlox has a diversity of growth and life forms. Though some species are woody and others are annuals, most are herbaceous perennials, including the 11 varieties we have at the Arboretum. The genus name comes from the Greek word phlox, which means flame, and references the vibrant colors of the blooms that occur in some species and cultivars.
When choosing phlox varieties to plant in your garden, it is generally best to consider cultivars that are resistant to powdery mildew. Powdery mildew, root rot, phlox bugs, and even spider mites are all issues you may face when growing phlox in the landscape. Pruning back phlox after blooming or first frost is helpful to encourage growth and shape, and to discourage issues such as powdery mildew. Staking may also be necessary for certain taller garden phlox varieties.
P. paniculata, commonly known as summer phlox or garden phlox, is a Pennsylvania native and is highlighted the most in the Arboretum’s botanic gardens. Although this phlox is native to the north central and north eastern United States, it has escaped landscapes, naturalizing into areas beyond its native range. It is characterized by Missouri Botanic Gardens as “a staple of the perennial border.” A showy and upright plant, P. paniculata is light-loving and grows best in moist, organic, loamy soil. Typically, summer phlox reaches a height of 3–6 feet and forms a clump 2–3 feet wide. The specific epithet comes from “panicle,” in reference to the loose, branching cluster of flowers that develops at the top of each stem and blooms from June to August.
P. paniculata is very popular with pollinators including hummingbirds, butterflies, and bees! We have a number of P. paniculata cultivars in the garden and ‘Jeana’ is a particular standout. In 2017, P. paniculata ‘Jeana’ won a Mt. Cuba trial, displaying mildew-free foliage and the highest rate of butterfly attraction despite having smaller blooms than most other summer phlox. We can attest this is true after seeing it perform in the Pollinator and Bird Garden!
Other cultivars include P. paniculata ‘Laura,’ a mildew-resistant variety, that has large, vibrant pink-magenta or lavender clusters with a white eye. P. paniculata ‘David’ blooms in a striking white. Most of these cultivars can be found in the Rose and Fragrance Garden, the Childhood’s Gate Children’s Garden, or the Pollinator and Bird Garden.
P. paniculata is not to be confused with a commonly observed invasive species called dame’s rocket (Hesperis matronalis)! This Eurasian biennial belongs to the mustard family and is often misidentified as phlox due to its similar flower clusters, colors, and spring bloom-time here in Pennsylvania. It is a prolific seed producer and has naturalized itself in moist, woodland areas (occasionally in open areas, too) since it was introduced to North America in the 1600s. You can easily differentiate between species by looking at the number of petals on each bloom. Dame’s rocket has four petals while P. paniculata has five. You can read more about this species and view photos in this blog post by Penn State Extension!
Another species of native phlox that can be found in the gardens is P. subulata. Also known as moss phlox or creeping phlox, it is a low-growing, mat-forming, sun lover. While this species only reaches a height of six inches tall, it can spread to two feet wide and is often used as groundcover in landscaping. The specific epithetic comes from the Latin word subulata, meaning awl-shaped, in reference to P. subulata’s leaves. Moss phlox has a spring blooming period, typically flowering from April through May.
Now’s the perfect time to stroll through the gardens and enjoy phlox before they slow down significantly in September and our fall displays take the spotlight! With prominent, long-lasting blooms and frequent pollinator buzz, there’s no mistaking the flame-like beauty of this summer star! You can find locations of phlox, photos, and more by searching our plant collections database.
