Chrysanthemums, commonly known as mums, are valued for their vibrant late-season color. The speed at which these plants develop changes based on their stage of life and the environment they are grown in. Understanding a mum’s growth rate involves knowing its seasonal expansion metrics and the conditions that influence its development. This article explores the measured rate of mum growth and the cultivation practices gardeners use to manage size and flowering time.
Defining the Growth Rate
Under optimal growing conditions, a newly planted chrysanthemum achieves its full size in a single season. Most garden varieties expand up to 3 feet in height and width by the time they bloom in the fall. This seasonal growth is divided into two distinct phases: initial rooting and vegetative growth.
The vegetative phase, which focuses on developing stems and leaves, begins after planting and lasts approximately four to five weeks. During this period, the plant establishes its root system and often reaches 20 to 24 inches in height. After this stage, the plant enters a rapid expansion phase. New shoots quickly emerge from the crown to form a dense, mounding shape before flower buds are set later in the summer.
Factors Determining Growth Speed
The actual rate of growth is heavily dependent on specific environmental conditions. Light exposure is a primary driver, as mums require a minimum of six hours of direct, unfiltered sunlight daily to fuel their development. Insufficient light results in a leggy, slow-growing plant that struggles to build the dense, bushy habit they are known for.
Soil quality also plays a role, as chrysanthemums perform best in well-drained, organically rich soil with a slightly acidic pH (5.5 to 6.5). Heavy, waterlogged soil leads to root issues that slow the plant’s progress by limiting nutrient and oxygen absorption. Consistent soil moisture is necessary for uninterrupted growth, since water stress causes an immediate slowdown in development.
Temperature provides the final component for rapid growth, with the ideal range occurring around 68°F (20°C). The optimal temperature for the vegetative phase is approximately 70°F during the day and 61°F at night. Temperatures significantly outside this range delay the plant’s progression through its growth stages, pushing back the final bloom time.
Managing Growth Through Cultivation
Gardeners can actively manipulate the growth speed and final shape of the chrysanthemum through cultivation techniques. “Pinching” is the primary method used to control size and encourage a dense, multi-stemmed structure. This involves removing the top inch of a new shoot when it reaches 6 to 8 inches in height. Pinching temporarily halts vertical growth and forces the plant to branch out laterally.
Pinching should be repeated every two to three weeks, typically from spring until mid-July, to maintain a compact form and uniform size. Consistent pruning during this period sacrifices some initial height but results in a bushier plant with a greater number of flower buds. This technique affects the growth rate by redirecting the plant’s energy from a single, tall stalk into many smaller branches.
Proper fertilization provides a direct boost to growth, as mums are considered heavy feeders during the vegetative stage. Applying a high-nitrogen fertilizer, such as a 20-10-20 blend, in the spring and early summer accelerates the production of leaves and stems. Once the plant approaches flowering, switching to a bloom-focused formula, like 5-10-5, supports the transition to flower bud development.
Growth Cycles of Mums
The overall growth timeline depends on whether the plant is a perennial or is treated as an annual. Hardy perennial mums, which are planted in the spring, develop an established root system that remains in the ground through the winter. This established system allows for a fast re-emergence and initial burst of spring growth in subsequent years, as the plant does not need to regrow its entire root base.
Conversely, the florist mums sold in the fall are treated as annuals because their growth is concentrated into a single season. These plants prioritize blooming over developing the robust root structure necessary for winter survival. For these single-season plants, their entire 3-foot growth potential must be achieved rapidly within the few months between planting and the first hard frost.