From our perspective as plants, our flowering is not dictated by a calendar but by the changing length of daylight, a phenomenon you know as photoperiodism. We are what is called "short-day plants." This is a slight misnomer; it is not that we require a short day, but rather a long, uninterrupted period of darkness to initiate the complex biochemical process of forming flower buds. As summer wanes and the nights grow longer, a pigment in our leaves called phytochrome senses this critical dark period. Once this signal is consistently received, our internal hormonal balance shifts. The production of growth hormones (auxins) slows, and the signals for flowering (like florigen) are triggered, instructing our apical meristems—the growing tips—to stop producing leaves and start producing flower buds.
You often group us all under one name—"mums"—but we have distinct genetic lineages that dictate our schedule. For most of our garden-variety cousins (Chrysanthemum × morifolium), the natural flowering season is in the autumn. This is when the natural photoperiod perfectly aligns with our needs, typically from September through November, often until the first hard frost signals the end of our display. However, there is another group: the hardy or garden mums. These are perennial varieties bred for your colder climates. While they also bloom in fall, their lifecycle is geared towards surviving winter and re-emerging the following spring.
You may see us for sale in full bloom at garden centers in the spring. This is not our natural rhythm. This is a result of a practice called "forcing." Growers manipulate our environment in greenhouses, using blackout cloth to artificially extend our nights and mimic the long darkness of fall. This tricks our photoperiod sensors into believing it is time to bloom, regardless of the actual season outside. While this allows us to bring you color year-round, it can be a stressful process that deviates from our innate cycle.
While photoperiod is our primary clock, other environmental factors play a crucial supporting role. Temperature is a key partner. Warm days and cool, but not freezing, nights are ideal for strong bud development and vibrant color in our petals. Excessive heat can delay flowering or cause our buds to form improperly. Furthermore, our overall health dictates the quality of our bloom. Well-draining soil prevents our roots from rotting, allowing us to efficiently uptake nutrients. Adequate water is essential, especially during bud formation, as drought stress can cause us to abort our flowers to conserve resources for survival. The nutrients you provide, particularly phosphorus, support the immense energy expenditure required to produce our prolific displays.
