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

Care, Uses, Varieties of a Popular Perennial

tall garden phlox

The Spruce / Adrienne Legault

Tall garden phlox (P. paniculata) is a low maintenance plant that adds a burst of color and interest to the summer garden. The Phlox genus belongs to the Polemoniaceae, or "Jacob's ladder," family and tall phlox is valued especially for its large, long-lasting blooms The flowers bear a mild fragrance and come in a wide range of colors appearing in panicles at the tops of 3 to 4 foot stems. These perennials also attract hummingbirds and butterflies. As an additional bonus, their sturdy stems render them a great choice 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 on the variegated cultivars, such as 'Nora Leigh.' Unfortunately, the appearance of the leaves can be 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 problem, a disease known as powdery mildew, is rarely fatal but it can 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 it needs to get through the summer. Garden phlox attracts bees and other pollinating insects to the yard so you want to avoid spraying with insecticides or herbicides that can kill them.

Light

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

Soil

Garden phlox does best in fertile , moist soil with the biggest requirement being 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 problems of heat and humidity by adding mulch to 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 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. You can also direct sow seeds in spring as soon as the ground can be worked. Cover seeds lightly with 1/8 inch of soil. Germination should occur in 5 to 10 days.

Potting and Repotting Garden Phlox

If you plan to grow garden phlox in a container, you will need to pot 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 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. Due to its height, garden phlox grown in pots may need staking or some other form of support.

Varieties of Phlox

There are many varieties of phlox, although people generally think of either the commonly-grown creeping phlox (Phlox subulata) or garden phlox (Phlox paniculata). Phlox subulata stays short and creeps, while garden phlox is tall and upright. These two varieties serve different purposes in the garden. Creeping phlox is a ground cover, whereas garden phlox, with its greater height, is more likely to be found in the middle 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.
  • 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 so look for 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.

Garden phlox is not usually bothered by insect pests.

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