The florist’s chrysanthemum, formally known as Chrysanthemum morifolium, is a highly cultivated flowering plant and a staple in the global floral trade. The question of its height is complex because its natural growth pattern is heavily modified by human intervention and breeding. This species, often called a “mum,” has been bred for thousands of years to possess diverse flower forms and colors. The plant’s final stature is a direct result of its specific cultivar and the intensive growing conditions imposed upon it for commercial display, meaning its final size is rarely its genetic maximum.
Understanding the Typical Height Range
The natural potential of a garden chrysanthemum, when allowed to grow in a perennial setting, can be substantial, typically reaching between one and three feet in height. Certain varieties may approach a maximum height of four feet if left entirely unpruned, and these taller specimens are generally grown as garden or cut-flower varieties where vertical growth is desired.
The compact, potted specimen seen in florist shops represents a significantly reduced size. This “florist’s mum” is intentionally kept short, usually topping out between 12 and 24 inches tall. This difference is not due to unique genetics but results from commercial growers using techniques designed to stunt vertical growth and promote a dense, bushy form. The plant’s size is entirely engineered to fit the dimensions expected of a container plant.
Environmental and Cultivation Influences on Growth
The environment plays a primary role in determining a chrysanthemum’s rate of stem elongation. As a short-day plant, the chrysanthemum uses the decreasing length of daylight to signal the transition from vegetative growth to flowering. Long periods of light exposure encourage the plant to remain vegetative, which promotes stem growth and height.
Temperature is another significant factor in height control, as cooler temperatures slow down metabolic processes. Growing the plants at lower temperatures, particularly cooler night temperatures, tends to produce shorter, sturdier stems. Conversely, warmer growing conditions accelerate growth, leading to faster, but often weaker and more elongated, stems. High light intensity provides the energy needed for vigorous growth, which contributes to overall height and stem strength.
Active Methods to Control and Stunt Growth
Commercial growers and home gardeners use deliberate physical and chemical actions to manage the final height of chrysanthemums. The most common physical method is “pinching,” which involves removing the soft, terminal growing tip of the stem. Removing this apical bud eliminates the source of the growth hormone auxin, which normally suppresses the growth of side shoots.
Pinching redirects the plant’s energy, promoting the development of lateral branches. This results in a wider, bushier plant with less vertical height, and the technique is often repeated during the vegetative phase to maintain a compact, mounding shape. Another element is “disbudding,” which is used to manipulate the final flower size by removing all but one of the flower buds on a stem, concentrating growth energy into a single, large bloom.
In commercial production, chemical Plant Growth Regulators (PGRs) are applied to achieve the desired compact habit of a florist’s mum. Chemicals like daminozide (B-Nine) and paclobutrazol (Bonzi) inhibit the production of gibberellins, the plant hormones responsible for stem elongation. A single application of these growth retardants chemically stunts the vertical growth of the plant, ensuring the stems remain short and the plant retains the dense, dome-like appearance expected of a potted chrysanthemum.