Creeping Phlox

Year-round

Creeping phlox is a low mat that likes moist, well-drained soil in part shade to sun.

• It grows 6 to 12 inches tall and spreads 9 to 18 inches wide.
• It prefers slightly acidic, well-drained soil.
• It is rated hardy in zones 4 to 8, so Harrisburg winters are fine.
• Maintenance is low.

Low, tidy mat that stays under a foot, so it works well along front walks and edges.

Fall

In fall, make sure air can move around the mat.

• Good airflow helps limit powdery mildew.
• Fall is a fine time to divide or take stem cuttings.
• Keep newly planted pieces watered until the ground freezes.

Winter

In winter, leave it alone.

• It is rated hardy to zone 4, well past Harrisburg winters.
• Skip pruning until spring growth begins.
• Keep heavy debris off the mat.

Spring

In spring, expect fragrant star-shaped blooms and keep new plantings watered.

• Flowers come in blue, purple, lavender, pink, or white.
• Keep new plants moist through their first year.
• Divide or layer stems now if you want to spread it.

Summer

In summer, water during hot dry spells, especially in year one.

• Once established it is very drought tolerant.
• Deadhead spent flowers to reduce powdery mildew.
• Watch for spider mites in hot dry spots and slugs in wet ones.

Year-round

Baseline care for creeping phlox (Phlox stolonifera), a low native groundcover for shaded and partly shaded spots in the Pittsburgh area.

• This groundcover is native to Pennsylvania. It grows naturally on wooded slopes and stream banks through the Appalachians, so it works as a native, HOA-friendly planting for a shaded bed or foundation edge.
• Give it morning sun or dappled shade. It struggles and can scorch in strong afternoon sun, especially through Pittsburgh's humid summer stretch.
• Plant it in moist, well-drained soil that is rich in organic matter and slightly acidic, like a woodland floor. Once established it handles short dry spells, but it does best with steady moisture.
• Watch the foliage for powdery mildew, a white coating that shows up most in still, humid air. Give plants room to breathe and water at the soil line instead of overhead.
• It spreads by rooting stolons instead of staying in one clump, so leave it room to fill in as a groundcover rather than treating it like a single specimen plant.

Fall

Fall in Pittsburgh, cooling down toward the first frost around mid October, is a good time to divide the mat and settle it in before winter.

• Divide and transplant sections of the mat in early fall while the soil is still warm, so roots can establish before the ground freezes.
• Cut back any tattered or mildewed foliage and clear fallen tree leaves off the mat so the semi-evergreen foliage underneath keeps getting light into winter.
• A light layer of mulch once the ground starts to cool helps even out soil temperature swings, but keep it off the crown of the plant.

A fall cleanup and light cutback keeps this groundcover looking neat along a walkway or foundation bed through the off season.

Winter

Creeping phlox is semi-evergreen, so it holds onto some foliage through a Pittsburgh winter and needs very little from you until spring.

• The foliage is semi-evergreen and can persist through winter rather than dying back completely, so the bed is not left bare.
• Skip pruning and feeding while the plant is dormant. Wait until after next spring's bloom to cut it back.
• Freeze and thaw cycles are common in the Pittsburgh area and can heave shallow-rooted plants partway out of the soil. A thin layer of mulch after the ground cools helps steady soil temperature, but keep it off the crown.

Its semi-evergreen mat holds a low, tidy green patch through winter in a front bed, when many nearby perennials have died back to bare soil.

Spring

Spring is bloom season for creeping phlox in the Pittsburgh area, and the best window to plant, divide, or tidy it up.

• Flowers open in April and carry into May, in white, blue, or purple depending on the variety.
• Once the last hard frost has passed, typically late April into May in the Pittsburgh area, it is a good time to plant new starts or divide and move established mats.
• After the blooms fade, shear the mat back by about a third. This tidies the bed, helps head off powdery mildew before summer humidity builds, and pushes fresh foliage.
• Slugs can chew ragged holes in the leaves in wet spring soil. Keep mulch off the crown and water in the morning so foliage dries by evening.

Shearing back the spent flowers in late spring keeps a front bed or foundation planting looking tended.

Summer

Pittsburgh summers are hot and humid, which is exactly the weather that lets powdery mildew take hold on phlox foliage.

• Keep the soil evenly moist through hot, dry stretches, especially for plants in more sun. Established plantings in shade tolerate short dry spells better.
• Powdery mildew risk climbs with summer humidity and still air. Thin out crowded patches and water the soil rather than the leaves to keep foliage drier.
• The mat can look tired by midsummer after its spring flush. A light trim keeps it dense and tidy without harming the plant.
• Skip fertilizer during the heat of summer. This is a low-input groundcover, and heavy feeding mostly encourages more mildew-prone growth.