Creeping phlox (Phlox subulata) is a popular, mat-forming perennial celebrated for its intense carpet of color during the spring season. It is highly effective as a groundcover, thriving particularly well in rock gardens and on slopes. While generally low-maintenance, regular trimming is necessary to maintain its tidy appearance and encourage dense, healthy growth. The following techniques cover essential steps, from routine annual maintenance to more intensive restoration.
Why and When Trimming is Necessary
Trimming creeping phlox serves several functions beyond simple aesthetics, primarily acting as a restorative process. Shearing prevents the plant from becoming “leggy,” a condition where the center of the mat thins out and becomes woody while the outer edges grow outward. Removing spent flowers and foliage redirects the plant’s energy away from seed production and toward developing new lateral buds and shoots, resulting in a denser mat of green growth.
The best time for trimming is immediately after the main spring bloom has completely faded, typically between late May and mid-June. This timing allows the plant sufficient time to produce a flush of new foliage before mid-summer heat and fall cooling. Timely shearing may also encourage a second, lighter flush of sporadic blooms later in the season. Avoid pruning late in the summer or fall, as new growth will not have time to harden off before winter, making it susceptible to cold damage.
Step-by-Step Guide to Routine Trimming
Routine annual trimming is best accomplished using sharp, clean tools, such as garden shears, hedge clippers, or a string trimmer held horizontally. Before beginning, sterilize your tools with rubbing alcohol or a mild bleach solution to prevent the transmission of plant diseases. The goal of routine trimming is a light “haircut” that removes faded flowers and a small portion of the vegetative growth.
The standard recommendation is to shear back the plant by approximately one-third of its green foliage, but not more than one-half. Cut just below the spent flower heads and into the green, leafy stems, stopping before reaching the older, woody stems underneath. Cutting into woody parts should be avoided during routine maintenance, as these stems often do not readily produce new foliage and can leave brown, bare patches. After shearing, gently remove the clippings to ensure good air circulation and light penetration to the center of the plant.
Rejuvenation Pruning for Overgrown Plants
When creeping phlox has been neglected for several years, it may become severely overgrown, exhibiting a thin, woody center with sparse foliage only on the outer edges. For these plants, a more aggressive process known as rejuvenation pruning is necessary to restore vigor and a dense habit. This method involves cutting back the plant much harder than a routine trim, often removing 50% or more of the plant material.
Rejuvenation cuts can be made slightly into the woody bases of the stems, stimulating latent buds to produce new growth. This drastic measure should only be employed when the plant’s health is suffering significantly, as it sacrifices the potential for blooms for the current season. The best timing for this severe cut remains immediately after the spring bloom, providing the longest possible recovery period. The goal is to force the entire plant to generate fresh, dense growth from the base, resulting in a fuller, healthier mat in the subsequent season.
Post-Trimming Care and Maintenance
Immediately following any trimming, especially severe rejuvenation pruning, the plant requires focused care to support recovery and new growth. The most important immediate step is to provide thorough watering to the trimmed area. This helps mitigate the stress of defoliation and ensures the roots have adequate moisture to fuel the development of new shoots.
After watering, the plant benefits from the application of a balanced, slow-release fertilizer, such as a 10-10-10 formulation, or a layer of compost. This provides necessary nutrients to support the rapid flush of green growth that pruning aims to stimulate. Ensure the fertilizer is applied around the plant, not directly on the foliage, and avoid high-nitrogen fertilizers which encourage excessive, weak growth. Continue to monitor the trimmed phlox for the next several weeks, ensuring the soil does not dry out and watching for signs of pest or disease issues.