How does a mum know it is fall?
Garden mums grow green and leafy through spring and early summer, and then, late in the year, they burst into bloom. Nobody tells them the date. So how does a mum know when it is time?
A plant scientist at the University of Missouri explains it: “Chrysanthemum is a good example of a short-day plant that flowers in response to the length of day versus the length of night.” Then he gives the order of events: “As days become shorter (and nights become longer) in late summer, flower buds form. Later, when days become even shorter, the buds develop and bloom.” So a mum does not read a calendar. It reacts to the dark: when the nights grow long enough, it starts making buds.
Basis: David Trinklein, University of Missouri, “Chrysanthemum: King of the Fall Flowers,” Missouri Environment and Garden (Integrated Pest Management), October 1, 2021. Quotations unchanged.
Look closely at one mum “flower” and you are really looking at a crowd. “The flower of a chrysanthemum actually is a compound inflorescence consisting of many small flowers (a.k.a. florets).” There are two kinds: “Those that we commonly call petals are ray florets, which typically are found around the perimeter of the inflorescence. In the center of the flower are the shorter and less showy disc florets.” The same article says mums have a long history with people: “The first chrysanthemums probably were cultivated in China as many as 2000 years ago.”
Basis: David Trinklein, University of Missouri, “Chrysanthemum: King of the Fall Flowers,” Missouri Environment and Garden (Integrated Pest Management), October 1, 2021. Quotations unchanged.
Not every mum is the same kind of mum. The article says the name hardy chrysanthemum has been dropped “(more or less) in favor of garden chrysanthemum,” while “Florist chrysanthemum, on the other hand, is a term applied to greenhouse-grown potted or cut mums not considered to be winter hardy.” (Winter hardy means able to survive a cold winter outdoors.) Garden mums also have an unusual talent: “Chrysanthemum is one of the few garden flowers that may be transplanted into the garden when in full bloom without doing serious detriment to the plants or flowers.” And “Container-grown chrysanthemums are readily available in the fall to enjoy.”
Basis: David Trinklein, University of Missouri, “Chrysanthemum: King of the Fall Flowers,” Missouri Environment and Garden (Integrated Pest Management), October 1, 2021. Quotations unchanged.
The mums quiz counts garden mums sold in pots. Put the facts above together and a guess appears: a plant that blooms in the fall, and that can be moved into a garden even while it is in full bloom, is a good plant to sell already flowering, in a pot, in the fall. That may be part of why pots of blooming mums show up in autumn. But this is this site’s own reasoning — the article does not say it, and it does not explain why New Jersey’s growers sell more garden mums in pots than any other state’s. That part is still a mystery.
※ A hypothesis is an idea that isn't proven yet.
📊 Sources for the rankings mentioned in this note (links to the original data and retrieval dates) are on each quiz page below.