Mums are widely celebrated as the quintessential flower of autumn, providing a burst of color when most other garden plants have faded. During the summer months, the plant’s appearance is distinctly different from its familiar fall display, as this period is dedicated to vegetative growth. For the home gardener, understanding this summer phase is the distinction between a sparse, leggy plant and the dense, flower-covered mound expected in late September and October. The summer is when the plant’s structural foundation is established, ensuring a robust bloom later in the year.
Summer Foliage and Structure
In the summer, a garden mum presents as a dense, leafy green shrub. The foliage is dark to medium green and features a deeply lobed structure, often described as coarsely toothed or serrated, with an alternating arrangement along the stems. The leaves have a slightly thick texture and can sometimes feel rough to the touch, distinguishing them from many softer summer annuals.
The overall shape depends heavily on cultivation practices. A well-maintained mum will exhibit a compact, dense, and naturally rounded or mounding habit, typically reaching 1 to 2 feet by mid-summer. Conversely, plants that have not received structural care will appear taller and “leggy,” with soft stems that may struggle to support themselves and are prone to toppling over when heavy flower buds set in the fall.
The Growth Phase and Photoperiodism
Chrysanthemums are classified as short-day plants, meaning they require a specific period of uninterrupted darkness to initiate flower bud formation. During the long days of June and July, the hours of darkness are too short to trigger the reproductive cycle.
This sensitivity to day length is known as photoperiodism, a mechanism that controls the plant’s growth phases. When days are long, the plant prioritizes vegetative development, focusing energy on producing stems and leaves to build a larger structure. Flower bud initiation only begins when continuous darkness consistently exceeds a threshold, typically around ten hours. This critical change naturally occurs in late summer, usually starting in mid to late August in most temperate regions.
Essential Summer Maintenance
Because the summer season is dedicated to vegetative growth, active management is necessary to shape the plant for its spectacular fall display. The most important cultural practice is “pinching,” which involves removing the soft, new growth at the tip of each stem. This technique removes apical dominance, forcing the plant to branch out laterally from the nodes below the cut, resulting in a bushier, more compact structure.
Pinching should begin when the plant reaches about six inches tall in the spring and be repeated every three to five inches of new growth thereafter. Most gardeners cease all pinching by early to mid-July, often using the Fourth of July as a guideline. Stopping the pinching too late can delay the bloom time, risking the flowers to an early frost.
Watering and Fertilizing
Consistent moisture is important, as the actively growing plant requires a steady water supply during the heat of summer. Mums generally need about one inch of water per week, and the soil should be kept uniformly moist but never waterlogged. Watering directly at the base of the plant is recommended to avoid wetting the dense foliage, which helps prevent fungal diseases like powdery mildew. To support this vigorous growth, a balanced fertilizer should be applied monthly through late July or early August.
Addressing Early-Season “Mums”
The appearance of blooming chrysanthemums in garden centers during July or August often leads to confusion about the plant’s summer appearance. These early-flowering plants are typically not traditional perennial garden mums allowed to grow naturally, but rather “florist mums” chosen for commercial manipulation.
Commercial growers achieve these out-of-season blooms by intentionally manipulating the environment to simulate short-day conditions. This is done by covering the plants with black cloth for a portion of the day, artificially extending the hours of darkness to meet the ten-hour threshold needed for flower bud initiation. This controlled light exposure forces the plants to bloom much earlier than they would naturally. These greenhouse-forced plants are the exception and should not be confused with the dense, green, vegetative state of a perennial garden mum growing in a home landscape.