Mums (chrysanthemums) are known for their vibrant color in autumn when most other flowers fade. This association often causes confusion about the plant’s appearance during the rest of the year. Throughout spring and summer, the chrysanthemum focuses entirely on its vegetative phase. It dedicates energy to producing a robust framework of stems and leaves, which is the necessary foundation for the heavy blooms that emerge later.
Spring: Emerging Foliage and Basal Growth
As the weather warms, the chrysanthemum emerges from winter dormancy. Initial growth appears as fresh, green shoots, known as basal growth, rising directly from the crown near the soil line. These vigorous shoots form the current year’s structure, often measuring only a few inches early in the season.
The foliage is typically a deep green, with leaves that are deeply lobed or toothed, sometimes exhibiting a slightly fuzzy texture depending on the variety. At this stage, the plant is low-growing and compact, resembling a small, dense clump of perennial greenery. The focus during spring is on root development and establishing these new stems, which lengthen quickly as the days grow longer.
Summer: Developing the Dense, Bushy Structure
Warmer temperatures and extended daylight hours drive rapid growth in summer, transforming the small spring clump into a dense, rounded mound of green foliage. If left to grow naturally, a chrysanthemum stem becomes tall and spindly, producing only a few flowers at the tip. To prevent this “leggy” appearance and encourage a full, bushy shape, gardeners use a technique called “pinching.”
Pinching involves removing the soft growing tip of a stem, which eliminates the dominance of the apical bud. This action forces lateral buds along the stem to activate and grow into side branches. The result is a plant with multiple stems and a thicker, more compact structure. This process is repeated every few weeks until early to mid-July, ensuring the plant develops the maximum number of branches to support future blooms.
The Biological Reason for Delayed Blooming
Chrysanthemums remain green and vegetative throughout spring and summer due to a biological mechanism called photoperiodism. Mums are classified as “short-day” plants, meaning the duration of continuous darkness controls their flowering. These plants require a period of long, uninterrupted nights to trigger the switch from producing leaves and stems to developing flower buds.
During late spring and summer, the nights are too short to initiate this reproductive change. The plant senses the increasing length of the dark period after the summer solstice when the days begin to shorten. Once the hours of darkness exceed a specific critical length—often 12 to 13 hours—the plant signals the shift to flowering. This timing allows the plant the entire spring and summer to build the strong, bushy framework necessary for its late-season bloom.