Phlox offers color through two primary forms: the tall, upright garden phlox (Phlox paniculata) and the low-growing, spreading creeping phlox (Phlox subulata). While these plants are generally robust, focused maintenance is necessary immediately following their main flowering display. Proper post-flowering care is a direct investment in the plant’s health, aesthetic appearance, and its ability to return with vigor. Understanding the specific actions to take once the blooms fade ensures your phlox remains a healthy, long-lived feature in the garden.
Immediate Action: Deadheading Spent Blooms
The first step after phlox flowers fade is deadheading, which involves removing only the spent bloom clusters. This action prevents the plant from diverting energy into producing seeds, allowing it to redirect resources toward root growth and strengthening its structure. Use clean, sharp hand pruners to snip off the faded flower head. Make the cut just above the first healthy set of leaves or a visible side-bud beneath the spent cluster. Removing these blooms immediately improves the plant’s appearance and encourages the development of new flowering side-shoots.
Pruning Phlox for a Second Bloom
For tall garden phlox (P. paniculata), a substantial mid-season cutback can encourage a second, smaller flush of flowers in late summer or early autumn. Applied immediately after the initial wave of blooms has concluded, this technique stimulates dormant lateral buds to form new flowering shoots. Cut the entire stem back by approximately one-third to one-half of its total height, trimming stems down to a point just above a healthy leaf node. This aggressive pruning targets the entire stem length, resulting in a more compact plant habit. Creeping phlox requires a lighter touch; after its spring bloom, simply shear off the top few inches to tidy its shape and stimulate denser foliage growth.
Addressing Post-Flowering Health Concerns
The summer months following flowering are when phlox often becomes vulnerable to fungal diseases, particularly powdery mildew. This common ailment presents as a white or grayish coating on the leaves and stems, hindering photosynthesis and weakening the perennial. Sanitation is the most effective post-bloom defense against this fungus, which thrives in poor air circulation and high humidity. Immediately remove and dispose of any severely infected stems or leaves, discarding them away from the garden bed and not in the compost pile. Ensuring good airflow by avoiding overcrowding and watering the soil directly limits the spread of fungal spores, though selecting mildew-resistant cultivars is the best long-term strategy.
Preparing Phlox for Winter Dormancy
The final post-flowering action occurs in late fall or early winter, once the foliage of tall varieties has been killed back by a hard frost. This is the time for a complete, hard cutback, which serves a hygienic purpose. Cutting the remaining stems down to within two or three inches of the ground prevents the overwintering of pests and fungal spores like powdery mildew. This thorough removal of dead plant material ensures that disease inoculum is not present to reinfect new growth in the spring. After the cutback, clean up all surrounding debris and apply a final layer of mulch for insulation, protecting the crown throughout its dormant phase.