HARDINESS: Zones 3 to 9
PREFERRED SOIL pH: Slightly acid
PREFERRED SOIL TYPE: Organically rich
PREFERRED LIGHT: Sun to partial shade
ATTRIBUTES: Long-fasting while or pastel flowers on tall plants; for beds, woodlands
SEASON OF INTEREST: Midsummer through fall
FAVORITES: Mildew-resistant 'David', Robert Poore'; bicolored 'Eva Cullum'
QUIRKS: Produces second crop of flowers if cut back when initial flowers fade
GOOD NEIGHBORS: Ageratum, artemisia, daylily, obedient plant
WHERE IT GROWS BEST: Fertile soil with morning sun and afternoon shade
POTENTIAL PROBLEMS: Powdery mildew; spider mites, phlox bugs
RENEWING PLANTS: Lives many years; divide crowded clumps every 3 years
CRITTER RESISTANCE: Good
SOURCE: Bedding plants, division
DIMENSIONS: 2-4 ft (0.6-1.2 m) tall, mature clumps 2-4 ft (0.6-1.2 m) wide
Garden Phlox in the Landscape
In midsummer, when many flowering plants go dormant and butterflies have a harder time finding nectar, garden phlox emerges and becomes a meeting place for winged creatures. A North American native, garden phlox are tall, upright plants that inhabit woodland clearings near streams and rivers. Cultivars have been developed for garden performance that bloom more heavily than the wild species. These stand 3-5 ft (1-1.5 m) tall and produce rounded flower clusters composed of dozens of 1 / 2 in (1.2 5 cm) wide fragrant pink, white, lavender, and rose blossoms. The oval leaves are medium green but tend to be a bit darker when plants are well fed and grown in partial shade.
Garden phlox likes plenty of sun and fresh air around its top growth but wants its roots to be cool and moist. In cold climates grow garden phlox in sun and keep it well mulched at all times. In Zone 7 and warmer climates, garden phlox will bloom much stronger and longer if the plants are shaded in the afternoon and topped with an organic mulch.
The Healthiest Beauties
Plant breeders have had great success coaxing beautiful colors out of pink-blooming ancestral strains, resulting in cultivars, such as 'Franz Schubert', which has soft lilac flowers, each accented by a white center. Flowers in red shades are available, as are some varieties with variegated foliage, but these unusual types tend to be smaller and less vigorous than the white-, pink-, or lavender-blooming cultivars.
In recent years the nursery industry has promoted garden phlox with good resistance to powdery mildew, a fungal disease that strikes when days are warm and humid and nights are cool, causing unsightly white patches on leaves but not killing the plants. Cultivars with superior mildew resistance include the pure white 'David', the pure pink 'Robert Poore', and 'Eva Cullum', which bears pink flowers with an almost red central eye. In areas prone to powdery mildew, thin plants to increase air circulation and avoid wetting the leaves when irrigating to help prevent the disease.
Insect pests rarely visit phlox, but sap-sucking spider mites may give leaves a pale, stippled appearance. They are most active during droughts and can be eradicated by hosing off foliage early in the day so that it dries before evening, when mildew problems are likely to develop. If leaves show holes left by beetlelike phlox bugs or other chewing pests, spray plants with a botanical, neem-based insecticide as directed on the label.
Set out purchased plants in early spring. Sprinkle compost or other organic matter into each planting hole and set the plants so that the roots are covered with 1 in (2.5 cm) of soil topped by another 2 in (5.1 cm) of organic mulch. Keep the roots evenly moist during the first summer after planting. To prolong flowering for many weeks, cut off old flower clusters to encourage new buds to form. Cut stems back close to the ground in winter, after plants become dormant.
Fertilize garden phlox in spring with an organic or controlled-release fertilizer. Every 3 years, or when plants become crowded, dig up the clump in early spring, separate individual plants, and replant them after renewing the site by digging in organic matter, such as compost.