Phlox

In the Garden

Ralph Purkhiser, Purdue University Master Gardener

     The last of the flowering plants being honored this year by the National Garden Association is one that is familiar to most gardeners.  In the perennial category, 2022 is the Year of Phlox. 

     There are over 65 species of phlox, and all but a couple are true perennials, meaning they will come back in the garden for multiple years.  Most are native to North America, but a couple are found in Siberia.  Phlox is a genus that was exported to Europe soon after European exploration of the Americas began, and breeding efforts have spanned several centuries.  The European breeders are now sending some wonderful new cultivars back to America.

     Phlox are divided into two main groups: groundcover phlox and tall phlox.  Both types have five-petal flowers that appear in large panicles.  In fact, the name phlox comes from the Greek word for flame.  The flowers may be red, pink, purple, blue or white, and many of the new cultivars have bi-color flowers.  Most groundcover phlox bloom in the spring, and the tall phlox bloom in the summer and fall.

      Phlox do best in full sun, but anyone who has seen the wild tall phlox knows that some shade is tolerated.  However, flowers growing in the shade tend to flop over easily.  They like a rich soil with good drainage, preferring a sandy loam.  If you lack that soil, you can amend the soil with plenty of compost.

     The tall phlox will often re-bloom, especially if they are deadheaded.  However, if you do not deadhead, the plant will set seed, which will fall to the ground and result in more plants.  These seedlings sometimes offer some surprises, as various cultivars cross readily.  The root system is stoleniferous, meaning that the plant develops horizontal roots that will increase the size of a clump in a couple of years.  To ensure the plants perform well, most will benefit from dividing every three to five years.

     Phlox flowers are loved by pollinators, especially butterflies.  They are even host plants for a couple of butterfly species.  The tubular flowers are also a good nectar source for hummingbirds and bees.

     The biggest enemy of phlox is powdery mildew.  Some of the new cultivars have been bred for resistance to this fungal disease.  Otherwise, you may need to treat the foliage with a fungicide.  Once the fungus starts, there is nothing you can do except cut the plant down and dispose of the diseased foliage.  Good air circulation will help to prevent the fungal disease.  You should never use an over-head watering system when watering phlox, as wet foliage invites fungal problems.

     Some phlox blooms are very fragrant.  My personal favorite is a white cultivar named “David”, the scent of which is among the most pleasant odors in the garden.  The blooms are also long-lasting and the flower clusters are very large.  This wonderful plant has earned a prominent spot in my moon garden.

     In fact, phlox cultivars exist for about every garden spot where there is a reasonable amount of sunlight.  The creeping phlox and moss phlox are great groundcovers for banks.  Some have evergreen foliage, so they even look good when not in bloom.  Native woods phlox add some bright flowers in marginal areas at the edge of shade gardens.  The perfume of scented cultivars make those plants great for sensory gardens.  I even planted phlox in a Bible garden.  After all, the shepherds were guarding their phlox at night.