Creeping phlox (Phlox subulata) is a low-growing, mat-forming perennial prized for its brilliant spring bloom and dense habit. This plant typically grows only four to six inches tall, but spreads vigorously, creating a thick carpet of foliage. Its ability to spread and form a tight mat makes it particularly valuable for stabilizing soil on sloped areas. The dense network of shallow, fibrous roots helps bind the topsoil, acting as an effective barrier against surface erosion and runoff.
Preparing the Planting Site
Preparing the sloped site is foundational to successful creeping phlox planting. Locating the site where it receives at least six hours of direct sunlight is necessary for optimal flowering, though it can tolerate light afternoon shade in hotter regions. Phlox prefers well-drained soil, which is often naturally present on slopes, but it must not be excessively dry or compacted. You can verify drainage by digging a twelve-inch-deep hole and filling it with water; a draining rate slower than one inch per hour indicates poor drainage that requires amending.
Before planting, clear the area of weeds, grasses, and debris that would compete with the new plants. Slopes often have heavily compacted soil, which hinders root establishment, so the entire planting area should be loosened to a depth of four to six inches. Incorporating organic matter, such as compost, into the loosened soil improves both drainage and nutrient retention, giving the young phlox a better start. The goal is to create a soft substrate that encourages the shallow roots to spread quickly and anchor the soil.
Techniques for Securing Plants on an Incline
Planting on a slope requires specific techniques to counteract the effects of gravity and water runoff. For effective erosion control, plants should be spaced close together, typically between 12 and 18 inches apart, to ensure the phlox forms a solid, protective mat quickly. The key to planting on an incline is to position the plant so it is angled slightly upward, with the base of the stem pointing toward the top of the slope. This orientation helps the plant settle securely into the hillside and reduces the chance of the root ball washing out during heavy rain.
Dig each planting hole wide enough to accommodate the root ball comfortably. Use the excavated soil to create a small, semicircular berm on the downhill side of the hole. This soil ridge acts as a catch basin, trapping water long enough to soak into the root zone instead of immediately running down the hill. For very steep grades or areas prone to heavy runoff, install a biodegradable erosion control blanket, such as jute netting, across the slope before planting. Cut small, X-shaped openings in the blanket to insert the phlox, securing the netting with biodegradable staples every few feet to prevent shifting.
Establishing and Maintaining Creeping Phlox on Slopes
The most significant challenge when establishing plants on a slope is ensuring water penetrates the soil rather than running off. New creeping phlox requires consistent moisture for the first year to develop a deep, robust root system. The most efficient way to achieve this is through drip irrigation or soaker hoses laid along the contour of the slope, directly next to the plants. This low-volume method delivers water slowly, allowing it to soak in gradually without creating runoff or dislodging soil.
If a drip system is not feasible, employ a “cycle and soak” hand-watering method, applying water in short bursts and pausing between cycles to permit absorption. This prevents the formation of a surface sheet of water that would otherwise rush downhill. A light layer of shredded mulch, such as wood chips or pine needles, can be spread between the plants to conserve moisture and reduce runoff. Keep the mulch away from the phlox stems to prevent rot. Once the spring bloom finishes, lightly shear the spent flowers and stem tips, removing about one-third of the growth to encourage denser foliage, which improves the plant’s ability to stabilize the hillside.