Phloxes are a surprisingly diverse bunch of plants for a single genus. Some are tall, fragrant, sun-loving perennials, while others have leaves that look like moss and grow close to the ground.
The World of Phloxes
Besides their array of physical forms, cultural requirements also vary among the different phlox species, so it's best to break them up into categories and consider each on its own merits. All the following are readily available in garden centers throughout the country.
These phloxes bloom in late summer and prefer full sun, regular water and average garden soil.
Phlox paniculata, commonly referred to as garden phlox, is the most widely grown of the tall sun-loving phlox varieties and is a parent of the most of the available hybrids. Growing two to four feet tall on single erect stems topped with softball-size flower clusters, it is a mainstay of the perennial flower border. It is hardy in USDA zones 4-8.
Garden phlox flowers come in every color of the rainbow and many are intoxicatingly fragrant. Its foliage is nondescript and often becomes scraggly on the lower portions of the plant, so it's best to plant garden phlox at the back of the border with low and spreading plants in the foreground.
Stake the top-heavy stalks if needed and cut of the spent flower heads to encourage repeat blooming. The entire plant can be cut to the ground in fall. Every few years, dig up the clump and divide it to keep the phlox patch healthy and flowering abundantly.
Cultivars Are Powdery Mildew Resistant
The Achilles heel of garden phlox is its susceptibility to powdery mildew. This can be treated with fungicides but it's best to avoid the problem by planting mildew-resistant cultivars, a few of which are listed below.
- 'David' has pure white flowers; USDA zones 3-9
- 'Eva Cullum' has pink flowers with red eyes; USDA zones 4-8
- 'Rosalinde' has purple-pink blooms; USDA zones 4-8
These phloxes are suitable for the front of the perennial border and are a good choice for planting where they can cascade over stones or a retaining wall. They are also suitable as a small scale groundcover in the light shade of flowering trees or among spring-blooming bulbs. Groundcover phloxes bloom in spring and early summer.
Moss pink (Phlox subulata) is the most common type of groundcover phlox. Its leaves are so tiny and thin that the plants look like a patch of moss when not in flower. It grows just three to six inches in height and its flowers come in every color of the rainbow, often with frilly notches on the edges of the petals. It is hardy in USDA zones 3-9.
Moss pink and other groundcover phloxes are more tolerant of heat, drought and poor soil than their taller cousins; pests and disease are rarely a problem. They do need regular irrigation to stay lush, but otherwise require very little attention. Shear them back about 50 percent at the end of the growing season to keep dead foliage from building up between the stems.
Cultivars come in various colors.
- 'Crimson Beauty' has red flowers; USDA zone 2-9
- 'Millstream' is white with a red center; USDA zones 2-9
- 'Blue Emerald' has light blue blossoms; USDA zones 3-9
- 'White Delight' has white blossoms; USDA zones 2-9
There are a few types of phlox useful in woodland gardens and shady borders. The most common of these is known as woodland phlox (Phlox divaricata). This and other shade-loving phloxes grow on erect stems to about one foot in height and creep slowly across the ground to form small patches. Like the other varieties, flower color is all over the map. It is hardy in USDA zones 3-9.
Shade-loving phloxes like rich, moist forest soil. They are quite immune to pests and disease as long as their nutrient and moisture needs are met. The only maintenance is to cut them to ground in late fall and divide up the clumps every few years to prevent them from becoming crowded.
Some of the most ornamental cultivars include:
- 'Chattahoochee' has deep blue flowers with even darker purple centers; USDA zones 4-9
- 'Ariane' is white with a yellow eye; USDA zones 4-9
- 'Fuller's White' is a pure white variety; USDA zones 4-8
A Painter's Palette
All phloxes possess the same dainty flowers, but that's where the similarities end. Few other flowers come in such a wide spectrum of colors, and together with their diverse of growth habit and ability to fill so many niches in the landscape, phloxes offer a complete palette of options for garden design.