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How to Grow: Phlox
Tall garden phlox
Full sun, part sun
Bloom Period and Seasonal Color
Mid summer to fall in colors such as white, red, violet, purple, and bi colors
Mature Height x Spread
3 to 4 feet x 1 to 2 feet
attracts beneficials, attracts hummingbirds, native
This tall, native perennial puts on quite a summer flower show when planted in groups. This perennial is different from the creeping phlox (Phlox subulata) that hugs the ground and flowers in spring. Tall garden phlox grow up to 4 feet, creating a great backdrop to other perennials. They provide color in summer and fall when many other perennial flowers are fading. The clumps will slowly spread over time filling in an area and providing an even greater color punch. The flowers are good for cutting and are fragrant. Not only are the colors enticing to us, hummingbirds and butterflies can’t resist them. With their tall stature, phlox make good additions to the back of a perennial flower border.
Where, When and How to Plant
Phlox are hardy throughout our region. Purchase phlox from a local garden center or obtain divisions from a friend’s garden. Plant phlox in spring to early fall in full or part sun on well-drained, fertile soil. Amend the soil well with compost before planting because phlox grow best with high fertility. Space plants 2 feet apart.
Keep plants well watered and mulch with bark mulch in spring, keeping the mulch from touching the crown to prevent root rot. Fertilize each spring with a layer of compost.
Regional Advice and Care
Phlox will spread, so divide the clumps in spring every 3 to 4 years to create more plants to replant or share, reinvigorate the mother plant and to keep the plant in bounds. Powdery mildew is a big disease issue on phlox in our humid New England summer climate. Select disease resistant varieties, space plants further apart to increase air circulation allowing the leaves to dry out faster, and spray with an organic fungicide, such as Serenade, as soon as any signs of the white powder or yellowing leaves is seen on the plants. Deadhead spent flowers to prolong the bloom season. Cut plants back to the ground in fall and remove them after the flowering is finished and the leaves have yellowed.
Companion Planting and Design
Plant phlox in a perennial flower border with other fall bloomers such as Japanese anemone, goldenrod, asters, and chrysanthemums. To produce a stronger visual effect, plant them en mass and just let them spread to fill in the back of a flower border or even a meadow area.
“David” was one of the first mildew resistant varieties on the market and this white flowered variety is still one of the best. “Laura” is a purple flowered, mildew resistant variety that has a white flower center. “Volcano Purple” is a disease resistant, compact, 2-foot tall selection. “Bright Eyes” is a pink variety with red centers. “Franz Schubert” is an old fashioned lilac colored variety. “Starfire” is a cherry red variety.
Excerpted from my book, New England Getting Started Garden Guide.