How to Grow and Care for Garden Phlox (Tall Phlox)

Care, Uses, Varieties of a Popular Perennial

tall garden phlox

The Spruce / Adrienne Legault

The Phlox genus belongs to the Polemoniaceae, or "Jacob's ladder," family. The garden phlox species (P. paniculata) within that genus is valued for the long-lasting blooms it sports during the summer months. The flowers bear a mild fragrance and come in a wide range of colors. These perennials also attract hummingbirds and butterflies. As an additional bonus, their sturdy stems render them great choices for cut flowers.

Garden phlox grows in upright clumps, and it is a moderately tall perennial. In fact, "tall phlox" is another of its common names. The species name of paniculata refers to the "panicles" of blooms (flower heads) held atop its stalks. Occasionally, the foliage is also attractive, especially that on the variegated cultivars, such as 'Nora Leigh.' Unfortunately, the appearance of the leaves is often marred by powdery mildew. Learn how to grow and care for this classic plant for the cottage garden.

Botanical Name Phlox paniculata 
Common Names Garden phlox, tall phlox
Plant Type Herbaceous perennial
Mature Size 2 to 4 ft. tall, 2 to 3 ft. wide (but varies by cultivar)
Sun Exposure Full sun to partial sun
Soil Type  Moist but well-drained
Soil pH Neutral
Bloom Time Summer
Flower Color Lavender, lilac, pink, purple, salmon, white
Hardiness Zones 4 to 8, USA (but varies by cultivar)
Native Area Eastern United States
Volcano Ruby (image) is one of the tall phloxes. It blooms in August.
Volcano Ruby phlox David Beaulieu

Garden Phlox Care

Considering the value that garden phlox flowers add to a landscape, the care that they need is minimal. If located in a sunny spot and provided with a soil that drains well, they should thrive and come back year after year. Even their biggest nemesis, a disease known as powdery mildew, is rarely fatal to them; it will just spoil their looks a bit.

Deadhead the spent flowers on garden phlox to prolong the blooming period. Regularly weed around your plant so that weeds do not sap its strength or rob it of the water that it will need to get through the summer. But garden phlox attracts bees and other pollinating insects to the yard; avoid spraying with insecticides or herbicides that will kill them.

Light

Grow garden phlox in full sun in the North and in partial sun in the South.

Soil

The main soil requirement for garden phlox is good drainage.

Water

Keep the soil evenly moist, but do not overwater. Avoid overhead watering. Point the nozzle of your garden hose, instead, at an angle that will direct the spray at ground level. Keeping the foliage dry will minimize problems with powdery mildew.

Temperature and Humidity

Garden phlox does not like hot, humid summers, so it is not a good choice for gardeners in the Deep South. You can mitigate the problems that garden phlox has with the heat by providing it with mulch, which will keep the root zone cool.

Fertilizer

This plant wants a soil with moderate fertility. Fertilize garden phlox with compost each year in spring.

Propagating Garden Phlox

Propagate phlox plants is by dividing them in early spring. Dig your phlox plant out of the ground and split it into smaller clumps using a sharp knife. Then replant these clumps.

Potting and Repotting Garden Phlox

If you will be growing your garden phlox in a container, you will need to repot it properly to provide the plant with optimal growing conditions. The best soil to use in a container is a potting mix, since this product drains well. Avoid using garden soil, which is too likely to become compacted in a container. The result of compacted soil will be root rot caused by inadequate drainage, which can be fatal to your plant.

Varieties of Phlox

There are many varieties of phlox, although people generally think of either the commonly-grown creeping phlox (Phlox subulata) or of garden phlox (Phlox paniculata). Phlox subulata stays short and creeps, while garden phlox is tall and upright. As a result of these physical differences, the two are used differently. Creeping phlox is a ground cover, whereas garden phlox, with its greater height, is more likely to be found in the middle row or back row of a flower bed.

Another difference between the two is that creeping phlox is a spring bloomer, while garden phlox is a summer bloomer. Furthermore, Phlox subulata has needle-like leaves, some of which remain green throughout the winter, while the leaves of garden phlox are much larger and die back at the end of the growing season; they are narrow at both ends and flare out in the middle.

Other types of phlox include:

  • Drummond phlox (Phlox drummondii) is an annual species.
  • While less popular, there is another creeping phlox besides Phlox subulata. It is called Phlox stolonifera. Among other differences between the two, the latter tolerates partial shade, whereas Phlox subulata needs full sun to thrive.
  • Woodland phlox (Phlox divaricata): This perennial shares the feature of blooming in spring with creeping phlox, but its size is more reminiscent of garden phlox.
  • Spotted phlox (Phlox maculata) is a perennial similar to garden phlox both regarding bloom time and appearance. It has less of a problem with powdery mildew than does Phlox paniculata.
Nora Leigh phlox plants in bloom.
Nakano Masahiro/Getty Images
Closeup of 'Bright Eyes' tall garden phlox flowers.
'Bright Eyes' has a deep-pink "eye" surrounded by a lighter pink color. Maria Mosolova/Photodisc/Getty Images
Close-up of white flower head of 'David' phlox.
'David' is a white phlox cultivar. Garden Photo World/Georgianna Lane/Canopy/Getty Images
Several plants of 'Rosa Pastell' tall garden phlox growing together.
Gardeners who like pastel colors will want to grow 'Rosa Pastell' Mark Winwood/Dorling Kindersley/Getty Images
Closeup of flowers of Pink Flame tall garden phlox.
Flame Pink stays relatively short for a tall garden phlox. Courtesy of Proven Winners - www.provenwinners.com.
Closeup of flower head of 'Natascha' tall garden phlox.
'Natascha' has bicolored flowers. Maria Mosolova/Photodisc/Getty Images
Phlox paniculata 'Little Boy' with its bicolored flowers.
'Little Boy' has light centers and darker edges. Graeme Scott/Flickr/Public Domain
Tall garden phlox growing in mixed border with Rudbeckia fulgida.
Bjorn Forsberg/Photolibrary/Getty Images

Common Pests & Diseases

Garden phlox is susceptible to powdery mildew, a fungal disease that thrives under hot, humid conditions. Some cultivars of garden phlox, such as 'David,' are relatively mildew-resistant; grow these cultivars whenever possible. Other steps that you can take to prevent powdery mildew include:

  • Give garden phlox good air circulation by making sure to provide sufficient space between plants.
  • As part of your garden cleanup in fall, cut the stems down to the ground and remove them. Do not compost them if powdery mildew is present on any of the foliage.
Article Sources
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  1. Cox, Jeff. Perennial All Stars: the 150 Best Perennials For Great-Looking, Trouble-Free Gardens. Rodale Press, 2002