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Phlox

Phlox include a large group of mostly perennial plants widely used in gardens. Several hundred named varieties of different phlox species are grown. Because they are so commonly cultivated, it is little known that all phlox species are native to the United States. Many of these species are also native to the southeast or South Carolina. Because there are so many different species and cultivars, and they hybridize freely even in the wild, there is great variation throughout the genus. This can sometimes make definite identification to species difficult.

Mature Height/Spread

Numerous species of phlox are grown, with height varying between 3 to 6 inches for moss phlox (Phlox subulata) to 5 feet tall for the taller varieties of garden phlox (P. paniculata). Growth habit varies as well, from low, mounded sun-lovers, to low spreading woodland phlox with upright flower stems, to strongly upright narrow types.

Growth Rate

Phlox generally grow at a moderate to quick rate, depending on species, cultivar and growing conditions.

Ornamental Features

Phlox are grown for their abundant flowering, with most phlox species and cultivars also having a light sweet fragrance. Phlox are highly attractive to butterflies. Some species are so completely covered with flowers while in bloom that it is impossible to see any leaves. Wild species and virtually all cultivars bloom in the cool color range, ranging from white to pink, rose, red, magenta, purple, and blue. Some cultivars have flowers with multiple colors, often with a contrasting eye zone or petal edge. Flowers have five petals and are held in cluster above the foliage. Bloom time varies from early spring while daffodils are blooming to mid-to-late summer. Spring blooming species generally have a short, intense bloom period of 2 to 3 weeks, while summer flowering phlox may bloom over several months if old, spent flowers are removed regularly.

Culture

Tolerance of sun, shade, heat, and soil varies by species. For gardeners purposes, phlox can basically be divided into three groups of perennials – low growing sun lovers; low growing shade lovers; and tall, upright phlox that prefer sun or part shade. There is also one annual species. Low growing phlox for sun include hairy phlox and moss phlox. Low growing phlox for shade include woodland phlox and creeping phlox. Tall phlox include Carolina phlox, spotted phlox and garden phlox.

Propagation

Phlox may re-seed in the garden and seedlings will usually revert to the wild species coloration and habit over a few generations. If maintaining a particular color is important, self sown seedlings should be removed. Natural reseeding can be desirable in natural or wild gardens. Most phlox can be propagated by division or cuttings, and this will maintain the original variety true to type. Tall growing phlox should usually be divided at least every 3 years to prevent overcrowding.

CAUTION: Do not collect native wildflowers from natural areas, as this can lead to their eradication in the wild. Also, wild collected plants often do not survive transplanting. When purchasing native plants, be sure to buy plants that are nursery grown and propagated. Avoid companies that sell wild collected plants.

Problems

Powdery mildew is by far the worst and most common disease of phlox. It typically covers lower leaves with a grayish-white, powdery fungal growth in spring or late summer, and gradually works its way upwards on the plant. Powdery mildew can severely weaken susceptible phlox cultivars. Warm humid conditions favor powdery mildew growth and spread. Because these conditions are typical of South Carolina weather, it is important to take steps to prevent or control the disease.

Start by choosing species and cultivars that are known to have resistance to powdery mildew. Species vary considerably in their susceptibility. Generally, the low growing species are more resistant, while the tall growers are more likely to have problems. Within any species, there are cultivars that are more or less susceptible. Resistant cultivars are listed in the species descriptions below. Remember that resistant does not mean immune. Even highly resistant cultivars can develop powdery mildew if conditions favor its spread. Be sure to follow good cultural practices to help prevent powdery mildew infestation.

Promote good air circulation by giving plants adequate space. Phlox should never be crowded. Thin the number of stems in the spring to improve air movement through the plant in tall phlox. Keep plants growing strongly by providing the correct growing conditions for the particular phlox species. Never use overhead irrigation from sprinklers or hand watering. Always water at the base of plants to keep the air space around the foliage drier.

If powdery mildew is spotted early, remove any affected or fallen leaves. If the disease continues to spread it may become necessary to spray with a fungicide. At the end of the growing season cut back stems of deciduous species, and remove all fallen leaves. For more information on powdery mildew, and fungicide recommendations, see HGIC 2049, Powdery Mildew.

Spider mites are the most frequent insect pest, mostly occurring in hot, dry conditions on species that prefer moist soil.

Species & Cultivars

Some phlox, particularly garden phlox and moss phlox, are garden center staples. Others may take a little more searching to find, but are well worth the trouble. Some species are most easily found at nurseries that specialize in native plants, and these sources may carry a number of species in addition to those listed below.

Phlox have been extremely popular with gardeners and widely grown since their discovery in the late 18th century. Because of this they have acquired a wide variety of common names, some of which they share with completely unrelated plants. For this reason, knowing the botanical name will help ensure that you get the plant you want at nurseries.

Low Sun Loving Phlox Species

Hairy Phlox (Phlox amoena): This phlox is native to the southeastern US. In South Carolina it is found growing wild in the Piedmont and Midstate, into parts of the Sandhills. It will often be seen growing wild along roadsides. Hairy phlox is relatively low growing, reaching 12 to 16 inches tall in bloom. It spreads 12 to 18 inches wide. Flowers vary greatly in color form dark magenta, to blue, light blue or white and are lightly fragrant. It blooms between April along the coast and June in the mountains. The leaves are evergreen, narrow, leathery and covered with fine hairs.

Hairy phlox will grow throughout the entire state. It is very tolerant of hot humid conditions. This phlox prefers well drained, average to moist soil, but will tolerate dry, clay or sandy soils. It prefers full sun, but will tolerate some shade. For best appearance, cut back hard after flowering. Propagation is by cuttings.

Cultivars

  • ‘Cabot Blue’ is the most common type, with lavender blue flowers.

Moss Phlox (Phlox subulata): One of the most widely grown phlox, moss pink has acquired a variety of alternate common names including rock pink, thrift, ground pink, and creeping phlox. All these can be confusing at times, since they are shared with other unrelated plants and with a dissimilar phlox. Moss phlox is native to dry, rocky areas in the southeastern mountains. It is a tough plant, and forms an excellent, low, dense groundcover especially well suited for growing on slopes.

The evergreen leaves are needle like and form a dense carpet of foliage growing to only 3 to 6 inches tall and 12 to 15 inches or more wide. In early spring, from February on the coast to early April in the upper Piedmont and mountains, flowers cover the plants so completely that no leaves can be seen. The bloom season is short, but intense and highly valued as one of the earliest flowers. There are numerous cultivars with colors ranging from white to pale, medium and hot pink; lavender, pale blue, magenta, and striped flowers with a combination of colors. Many have contrasting eye zones.

Moss pink prefers full sun, and well-drained soil. It will tolerate poor soil, and withstands drought once established. Shade will cause plants to thin out, and they will not tolerate excessive moisture. Moss phlox is effective for erosion control on slopes once plants have closed together. To keep plants dense and improve appearance, either shear or mow with mower set at high setting after bloom is finished. Propagate by cuttings or by careful separation of rooted down stems along the edges of the plant.

Cultivars

  • ‘Appleblossom’ has soft pink flowers.
  • ‘Candy Stripe’ is bicolored, with white edges along pink petals. It is an attractive variety, both from a distance and up close where the striped detail can be seen.
  • ‘Coral Eyes’ has pastel pink flowers with bright coral pink eyes.
  • ‘Crimson Beauty’ has bright, rose red flowers.
  • ‘Dirgo Arbutus’ has lavender flowers with a darker eye.
  • ‘Emerald Blue’ and ‘Emerald Pink’ are dense, compact growers, with lavender blue and bright pink flowers.
  • ‘Millstream Daphne’ has deep pink flowers with a darker eye.
  • ‘Snowflake’ has pure white flowers.

Similar Species: Other low growing, sun loving phlox species include sand phlox (P. bifida), trailing phlox (P. nivalis) and downy phlox (P. pilosa). All are tough plants that thrive in sun and tolerate drought once established. Downy phlox is taller than the others, growing to 15 inches in height.

Low Shade Loving Phlox Species

Woodland phlox (Phlox divaricata): This shade loving species is also called wild sweet William or wild blue phlox. It is native to the eastern and Midwestern US, including South Carolina, growing in deciduous woods and along woods edges. Woodland phlox grows 12 to 15 inches tall in bloom, with the leaves forming a spreading mat. It blooms in early spring, about the same time as daffodils, and as hostas begin to emerge. It is a good cover for the leaves of earlier floweting spring bulbs. Flowers are fragrant and held in loose clusters. They can be blue, violet, lavender, pink or white depending on cultivar. The wild species flowers are blue to mauve. Leaves are 1 ½ to 2 inches long, semi-evergreen and narrow. This helps distinguish it from the similar creeping phlox (P. stolonifera), which has oval to rounded leaves. Woodland phlox is also taller than creeping phlox.

Woodland phlox can be grown throughout South Carolina, in proper growing conditions. This shade loving phlox prefers moist, fertile, woodsy soil, with plenty of organic matter in part to full shade. While morning sun encourages heavier bloom and denser growth, the plant will not withstand excessive sun. Be sure to maintain soil moisture in summer. Woodland phlox will go partly dormant in summer if the soil is too dry. Dry, hot conditions may lead to spider mite infestation. For best appearance trim off old flowers once it is done blooming. Woodland phlox rarely gets powdery mildew. Propagation is by cuttings or transplanting self-sown seedlings, which frequently occur in proper growing conditions. If given the correct growing conditions, woodland phlox is an easy, low maintenance plant.

Cultivars

  • ‘Chattahoochee’ is variously listed as a cultivar of a subspecies of woodland phlox or as a hybrid with downy phlox (P. pilosa). Whatever it’s parentage; it is a beautiful and popular plant. Flowers are fragrant, light blue with a purple eye. It is highly mildew resistant, and more sun tolerant than most woodland phlox.
  • ‘Clouds of Perfume’ has pale, silver blue flowers and blooms profusely. It is taller than most woodland phlox, reaching 18 to 22 inches tall in bloom. It is a healthy, vigorous plant, but is not more fragrant than the species or other cultivars.
  • Dirigo Ice’ is heavy blooming also, with icy blue flowers. It grows 12 to 18 inches tall.
  • ‘Fuller’s White’ is an excellent white flowered cultivar. It comes true to type from seed.
  • ‘Laphammi’ has large, lavender blue flowers, and blooms later than most other varieties. It grows 18 to 20 inches tall.
  • ‘Loddon Grove Blue’ is often sold as ‘London Grove Blue’. It has lavender blue flowers and is low growing.
  • ‘Louisiana Purple’ is an excellent, very vigorous growing plant, with abundant deep purple flowers.

Creeping Phlox (Phlox stolonifera): Creeping phlox is native to the South Carolina mountains and Piedmont in deciduous woods and along stream banks. It is similar to woodland phlox, but is lower growing with oval rather than narrow leaves. It forms an excellent groundcover, spreading by aboveground runners (stolons), and does well growing between other shade loving plants and small bulbs.

Fragrant flowers are held in loose clusters 6 to 12 inches above ground in early spring. Individual flowers are 1 to 1 ½ inches wide, in various shades of blue, violet, lavender, purple and white. The evergreen leaves are light green, and when the plant is not in bloom, form a low mat only 3 to 4 inches above the soil. It spreads quickly, but will not ever overwhelm other plants or become weedy.

Creeping phlox prefers moist, cool, well-drained soil, high in organic matter. It grows and flowers best in dappled shade or in morning sun and afternoon shade. Creeping phlox will not tolerate full sun in the south. Trim back lightly after spring flowering is complete for best appearance. It grows best in the mountains and Piedmont.

Propagate by cuttings, or by separating out small plants that develop on rooted sections of runners.

Cultivars

  • ‘Blue Ridge’ has violet blue flowers and grows to 6 inches tall.
  • ‘Bruce’s White’ has pure white flowers with contrasting yellow stamens in the center. It is more fragrant than most creeping phlox.
  • ‘Homefires’ is a vigorous cultivar with deep pink flowers.
  • ‘Sherwood Purple’ is an excellent cultivar with deep mauve flowers. It was Perennial Plant of the Year in 1980.

Tall Phlox Species

Carolina Phlox (Phlox carolina): Native to a wide area throughout the southeast, Carolina phlox is also native throughout South Carolina, growing in deciduous woods, forest edges and clearings, and along roadsides. It is closely related to garden phlox (P. paniculata) and spotted phlox (P. maculata). Carolina phlox has an upright growth habit, reaching 2 to 3 feet tall and 1 ½ to 2 feet wide. Flowers vary in color from lavender to pink to white. All these colors can also occur in wild plants. The flowers are held in small clusters at the top of the stems, blooming from May near the coast to late June in the mountains, earlier than garden phlox. Carolina phlox often flowers intermittently until the first fall frosts. Leaves are lance shaped, 1 ½ to 4 inches in length.

Carolina phlox will grow throughout the entire state. It prefers well drained soil, in full sun or some shade, and is heat tolerant. Cut back to 1 to 2 inches above ground level after the first fall frost. Propagation is by division in fall or cuttings.

While Carolina phlox is often said to be powdery mildew resistant; in trial plantings at NCSU, this has only been proven to be true of the straight wild species, which was highly resistant. Be sure to follow the cultural recommendations under the Problems section above to avoid mildew problems, particularly when growing the named cultivars.

Cultivars

  • ‘Miss Lingard’ is also commonly known as Wedding Phlox. It is very popular and the most commonly sold cultivar. Wedding phlox flowers are fragrant and pure white with gold stamens in the flower center. It has not proved to be mildew resistant in the southeast.
  • ‘Gypsy Love’ is shorter than most Carolina phlox, growing to 18 to 24 inches tall, with bright pink flowers. It is reputed to be mildew resistant, but trial results confirming this were unavailable.
  • ‘Magnificence’ is a tall selection, reaching 3 to 4 feet tall. Flowers are lavender pink. It is moderately mildew resistant.

Spotted phlox (Phlox maculata): Spotted phlox is also known as meadow phlox and wild sweet William, a common name it shares with some other phlox. It is native to the South Carolina mountains and usually seen along stream banks and moist roadsides. Closely related to Carolina phlox and garden phlox, these species sometimes cross naturally in wild. It can be distinguished from Carolina phlox by its thinner leaves and reddish spots or streaks along the stem.

Spotted phlox has a strongly upright habit, growing 2 to 3 feet tall and only 1 to 2 feet wide. Flowers are sweetly scented and range in color from pink to purple, lavender or white depending on cultivar. Flowers of wild plants are usually reddish purple. Blooming occurs in early to mid summer. Cut back the plant by half its height after summer bloom is finished to encourage repeat fall blooming

Spotted phlox prefers moist, but well drained soils rich in organic matter, in full sun to part shade. It is intolerant of drought and will need to be watered well during dry spells. Mulch over the plants roots to help conserve soil moisture. Spotted phlox is best suited for growth in the Piedmont and mountains. While more powdery mildew resistant than garden phlox, spotted phlox can still get the disease. Be sure to follow the cultural recommendations above under Problems to help avoid mildew. Clumps spread gradually by rhizomes and self seeding. Propagate by division.

Cultivars

  • ‘Alpha’, ‘Omega’ and ‘Delta’ are a series often advertised as mildew resistant. Unfortunately, in research trials in the southeast, they have all been fairly susceptible. ‘Alpha’ has lilac pink flowers; ‘Omega’ is very pale, almost white lavender with a pink eye. ‘Delta’ is light pink with a darker eye. All grow 2 ½ to 3 feet tall.
  • ‘Miss Lingard’ is listed above under Carolina phlox. She is sometimes listed as a cultivar of spotted phlox and may possibly be correctly placed in this species or may be a hybrid.
  • ‘Natascha’ has large heads of star-like raspberry-pink flowers striped with white on 2 to 2 ½ foot tall stems. It is fragrant and highly mildew resistant.
  • ‘Rosalinde’ grows to 2 ½ feet tall, with deep pink flowers and reddish stems. It has moderate mildew resistance.

Garden phlox (Phlox paniculata): This is by far the best known of the tall phloxes, very commonly grown in perennial borders. Unfortunately, many of its cultivars are the most prone to powdery mildew, and cultivar selection is very important for success. Garden phlox is native to the east coast and midwest, growing in the mountains South Carolina. It is very widely grown and garden plants have also escaped back into the wild.

Garden phlox is the tallest of the commonly grown species, reaching 3 to 5 feet tall depending on cultivar. The native species may grow even taller in ideal growing conditions. Individual flowers are 1 to 1 ½ inches wide, held in large terminal clusters 4 to 8 inches wide. The fragrant flowers may be magenta, pink, white, lavender, purple or blue, flowering from early to late summer. A few cultivars are orange. Wild plants usually are magenta to soft purple in bloom.

Garden phlox prefers fertile, moist, well drained soil, in sun to some afternoon shade. At least 6 hours of sun is needed for best flowering. However, some afternoon shade will help the plant deal better with summer heat stress. Overall, garden phlox is a tough plant, but powdery mildew is a chronic problem, especially at the end of the bloom season. Follow all recommendations in the Problems section above to reduce the chances for powdery mildew infection, beginning with selecting resistant cultivars. Be sure to provide good air circulation. Avoid crowding and thin plants to 4 to 5 strong stems in spring. Make sure that plants get sufficient sunlight. The wild species of is less susceptible to powdery mildew than many cultivars. Removing spent flower heads will encourage longer bloom. After first fall frost, cut plants to 2 inches above ground level and remove old stems and fallen leaves. Propagate by division or root cutting in fall. Stem cutting can be taken in early summer.

Cultivars

There are dozens of cultivars available of garden phlox and they vary widely in mildew resistance. Many state universities periodically trial powdery mildew resistance on phlox, but it is important to remember that conditions in the southeast strongly favor the disease. It is best to only choose cultivars recommended by reliable southeastern sources.

  • ‘Bright Eyes’ has light pink flowers with bright pink eyes. It has good mildew resistance.
  • ‘David’ is an excellent, fragrant white flowered selection from the wild, growing 2 to 3 feet tall. It is highly mildew-resistant, and often considered to be one of the two most mildew resistant cultivars, along with ‘Robert Poore’. 2002 Perennial Plant of the Year. 2000 Georgia Gold Medal Winner.
  • ‘Delta Snow’ is also an excellent fragrant white flowered cultivar that has done particularly well in trials in Georgia. It is vigorous, growing 3 to 4 feet tall, with good mildew resistance, and a long bloom period.
  • ‘Eva Cullum’ has medium pink flowers and deep pink eyes. It is long blooming, and has good mildew resistance.
  • ‘John Fanick’ has light pink with a darker eye. The flower heads are especially large. It has very good mildew resistance and is very drought and heat tolerant.
  • ‘Robert Poore’ has large heads of brilliant rosy-red to magenta flowers on vigorous 5’ tall plants. It is similar in appearance to the species but with brighter flower color. This is usually considered to be one of the most mildew resistant garden phlox cultivars. 2000 Georgia Gold Medal Winner.

Annual Phlox Species

Drummond’s Phlox (Phlox drummondii): The only commonly grown annual phlox, and often sold as simply annual phlox, this plant is native to Texas, but has naturalized through much of the southeastern U.S, including South Carolina. It is found growing wild throughout SC primarily in the central and coastal regions, often along roadsides. However, because it is not heat tolerant, Drummond’s phlox does not usually grow well in southern gardens, except where winters are mild enough for it to be grown as a winter annual for spring bloom. Heat stress will usually cause the plants to die out by early summer, unless they are very heat tolerant cultivars. Heat tolerant cultivars will slow or stop bloom in summer, but if given proper siting and care, may flower again in fall. In South Carolina, annual phlox is should be grown as a cool season annual.

Plants grow 6 to 15 inches tall, depending on cultivar and bloom profusely for their relatively short season. Flowers are fragrant, 1 inch wide in white, red, magenta, lavender, or pink and usually have a lighter-colored “eye” in the center. The wild plant’s flowers are usually rose red, but in South Carolina, color can vary considerably because wild plants are escapees from gardens. It is often included in wildflower seed mixes.

Annual phlox prefer sandy soil, with adequate but not excessive moisture. Six hours or more of morning sun with some afternoon shade will allow enough light for optimum flowering, while extending bloom time. Choosing heat tolerant cultivars will also lengthen the season of bloom. Keep old flower heads pruned off to further encourage continued bloom. Light fertilization of young plants will encourage growth. Avoid excess fertilization, particularly of high nitrogen fertilizers, which could cause excess leaf growth and delay flowering. Plants are usually and easily grown from seed. Seed can be sown directly in late winter or very early spring, or seedlings can be grown until 6 to 8 weeks old and set out a few weeks before the last frost date. Plants can also be set out in late summer for fall bloom. In more sheltered and warm areas along the lower coast, plants can be set out in mid-fall, much as pansies are planted, for earlier spring or even winter bloom. Plants may be found in cell packs in garden centers. Reseeding is common.

Cultivars

  • 21st Century series is a heat tolerant group that includes a variety of color selections and mixtures, including white, cream, red, pinks and lavender blue. Several of these have contrasting eyes. They grow to 10 inches tall and 10 inches wide.
  • Astoria series are very heat tolerant, with colors including white, pink, lavender, magenta and red. They are tall, reaching up to 24 inches tall and wide.
  • Intensia series is a vigorous group bred for heat and humidity tolerance, with a variety of colors. Plants grow 10 to 14 inches tall. Intensia phlox have rated well for heat tolerance in Georgia, Florida and Texas trials.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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