Goliath Phlox Tree: What It Is and How to Grow Tall Phlox

The term “Goliath Phlox Tree” sparks curiosity among gardeners, suggesting a plant of impressive size and stature. This guide clarifies the nature of this concept and provides insights into growing the tall phlox varieties it refers to. These plants can create a striking garden presence, leading to such evocative informal descriptions.

Understanding the Term Goliath Phlox Tree

“Goliath Phlox Tree” is not a recognized botanical classification for a tree species. Instead, it is an informal term describing exceptionally tall phlox varieties. Plants in the genus Phlox are herbaceous perennials; their stems die back each winter, unlike true trees with woody, permanent structures.

The “Goliath” descriptor refers to the impressive height these phlox varieties achieve, often leading observers to imagine them as small trees. Phlox paniculata, commonly known as garden phlox or tall phlox, are the likely subjects. While tall and upright, they lack the woody stems that define a tree. They are clump-forming perennials, returning from their rootstock each spring. This distinction is important for understanding their growth habits and care requirements.

Characteristics of Tall Phlox Varieties

Tall phlox varieties, primarily Phlox paniculata, are known for their upright growth habit and visual impact in garden settings. These herbaceous perennials typically grow 2 to 4 feet tall, though some cultivars can reach 5 feet or more, contributing to their “Goliath” perception. They form robust clumps, spreading 2 to 3 feet wide.

The foliage consists of narrow, elliptical, deep green leaves, often conspicuously veined, 4 to 6 inches long. These leaves are arranged oppositely along stiff, slender stems.

Tall phlox produces abundant, fragrant flowers in large, dense clusters called panicles. These showy clusters, 4 to 8 inches wide, bloom from mid-summer into early autumn, providing a long season of color. Flower colors span a wide spectrum including white, pink, red, purple, lavender, and bi-colors, often with a contrasting eye. Each flower is tubular with five flat, petal-like lobes.

Cultivating Tall Phlox Varieties

Successful cultivation of tall phlox involves providing appropriate growing conditions and consistent care to support vigorous growth and abundant blooms. Tall garden phlox thrives in full sun, ideally at least six hours of direct sunlight daily, though it can tolerate light shade, particularly in hotter climates. Ample sunlight promotes more vibrant and abundant flowering.

These plants prefer moist, fertile, well-draining soil with a pH of 6.0 to 8.0. Incorporating organic matter like compost or aged manure improves drainage and fertility. Consistent moisture is important for tall phlox, especially during dry spells, with about an inch of water per week. Watering the soil directly at the base of the plant rather than overhead helps reduce the risk of powdery mildew.

Applying organic mulch around the base of the plants helps retain soil moisture, suppress weeds, and keep the root zone cool. Fertilization can be done in early spring with a balanced, slow-release fertilizer or by adding compost. Deadheading spent flowers, which means removing faded flower clusters, encourages a second flush of blooms and prolongs the flowering season. Pinching back stems by one-third to one-half in early summer promotes bushier plants with more flower heads.

Good air circulation, achieved by proper spacing (18 to 24 inches apart) and thinning stems, is important for managing potential issues like powdery mildew, a common fungal disease. In late autumn or early spring, cutting plants back to the ground and removing plant debris from the garden helps minimize powdery mildew for the following season. Some taller varieties may benefit from staking for their flower stalks. Tall phlox can occasionally be affected by pests such as spider mites, aphids, and phlox plant bugs, which can be managed with horticultural oil or insecticidal soap.