The Strengths Behind Phlox subulata

Lowell Halvorson

Among the perennials, Phlox subulata often opens the category for early spring sales with vibrant color on the heels of pansies and forsythia. Early birds among the perennial-only crowd can safely plant it as long as the soil is workable. You know the classics: Emerald Cushion Blue, Drummond’s Pink, Purple Beauty, Candy Stripe, Fort Hill and so forth.

Yet their tall revenues tell a more complex tale. P. subulata sales continue after the blooms fade, unlike other early spring perennials. Their foliage covers the ground like a mat and comes across as a creeping juniper. Along rural roads, P. subulata guards no-mow zones by streets and fences. In urban neighborhoods with elevated yards, phlox covers areas where it’s tough to maneuver a mower.

P. subulata handles several practical roles in commercial developments. As a living mulch, P. subulata suppresses weeds and protects the soil, while tight, grippy roots stabilize the earth on slopes. Ground-hugging foliage can be trimmed with a machine and they spring back if the tires roll over them. Of course, phlox’s vivid, draping color is a natural brightener for terraces and retaining walls.

One finishing nursery on the East Coast sells half their P. subulata to landscapers. Early spring blooms see the biggest revenues, with replacement sales chugging through the summer. A second surge occurs when beds are planted in fall for spring color. This is a classic landscape sales rhythm.

Pictured: 1. Category tentpoles like Emerald Cushion Blue, Drummond's Pink and Snowflake are held in high regard by growers and breeders. 2. Trial GoldiPhlox White if nothing else. Pure whites lack vigor in this category, so the news of a strong clear white is promising. 3. Blue Moon is a tent among P. divaricatas, but Blue Ribbon has really neat foliage for the rest of the season. 4. Chicagoland Grows cross-bred P. subulata with
P. bifida to create the deepest blue to date.

It also solves a personal mystery. Why does Emerald Cushion Blue spank the other cultivars when Drummond’s Pink has more vibrant colors? Landscapers buy P. subulata when it’s green and the caliber of the green counts. Drummond’s Pink gets a bronzy dull look under heat stress, whereas Emerald Cushion Blue looks verdant, fresh and lush. Even in the winter, the plant stays evergreen as long as suffocating snows don’t fall.

Winter hardiness happens to be P. subulata’s strength and weakness: it’s chained to that sharp winter snap in order to bloom. The preferred strategy is to pot up in August and September so plants bulk up during autumn, vernalize over the winter, then bloom as soon as the hint of a growing season appears. If you have the space and calendar time, it works, but not everybody does. For a fast-finish P. subulata, source vernalized plugs with cell sizes as large as packaging allows.

Summer dormancy is the flip. P. subulatas fold their cards and sometimes don’t return to the table if summer heat gets too high or is too prolonged. You see them as staples in the Mid-Atlantic, the Carolinas, Southern Appalachia, the Central Plains, the Ozarks and dotted throughout the Mountain West. However, the Gulf Coast region turns away from P. subulata as a perennial. There, it’s used as a cute annual planted in February or March. Southern Texas often switches over to P. drummondii, a bright red annual phlox and a native son (but no relation to Drummond’s Pink).

Although the classics have the P. subulata character, well established and well respected, some areas of improvement do exist. One example is the timing window. P. subulata cultivars can bloom weeks apart from one another and the plants don’t hold well once in color. If you want to empty the house regardless of the color mix within, the GoldiPhlox series is just right. Bred for logistics, all six colors have consistent height and bloom within a week of each other.

GoldiPhlox White is especially promising. The current best-selling white, Snowflake, produces a pure, clean white with a beautiful habit, but the cultivar doesn’t grow much in the garden and tends to disappear after two or three years. A clear white that keeps up with the reds and pinks is worth investigating as a replacement.

Syngenta also offers Phlox Trot Pink, a gorilla among P. subulatas. Everything is just bigger. Each flower is the size of a quarter. A cutting is fuller, so you can stick one where you might have stuck two. Stems grow thicker before they fuzz out with needle-like leaves.

Proven Winners hybridized their P. subulatas with an eye towards overall vigor, a part of their bigger-is-better breeding style. The Spring Bling series mounds bigger and blooms with larger flowers. One flower does the work of two and the large size helps the blooms hang onto the stems longer for a wider season of color. The strength helps to resist the stresses of summer, and the habit moves away from low, knitted beds and more towards discrete mounding like decor specimens.

Although P. subulata has the landscaping strength, other phlox species have their own significant features for the garden center and breeding companies have locked onto them.

Darwin Perennials released the Spring Splash series at CAST this year. These are P. stolonifera hybrids that begin to bloom just as P. subulata falls off for the season. The flowers are similar, but the habit is puffed up and rounded in a decor style. Plants grow about a foot high and can handle light shade.

Following P. stolonifera is P. divaricata, comprised of woodland phloxes that thrive at the edges of meadows and forests. Today, that habitat translates to the yard-and-tree mix found in many home gardens and neighborhoods. P. divaricatas strongly prefer the dappled shade; do not plant them in full sun. Blue Moon and Blue Ribbons are the most popular varieties. Darwin also plans to release some new P. divaricata material next year.

Chicagoland Grows has released a couple of P. bifida hybrids, Violet Pinwheels and Perfectly Puzzling, and they plan to release more next year. Colors are more saturated and dappling is more common. GT

Lowell Halvorson is a consultant and writer in Fairfield, Connecticut, for retail and wholesale horticulture, specializing in business development. He also covers the breeding community for GrowerTalks magazine. You can contact him at (203) 257-9345 or halvorson@triadicon.com.