Few flowers say “fall” like mums do. They provide a burst of color at this time of year because they begin flowering after days become shorter. Several years ago, I also learned about the association between chrysanthemums and All Saints’ Day. Apparently, the tradition of placing them on graves for this occasion originated in France.
Mum is short for chrysanthemum. They’re in the aster or daisy family (Asteraceae) with plants like sunflowers, blackeyed Susans, zinnias, and other plants treasured for their cheery flowers. The mums that produce many flowers on a dome-shaped plant are commonly known as garden mums (Chrysanthemum x morifolium, formerly Dendranthema x grandiflorum).
When buying mums, you’ll likely find it more satisfactory to choose plants that are not yet in full flower. Instead, look for ones that have a lot of unopened flower buds.
While they’re sometimes thrown out after their fall flower display, garden mums are perennials and can be planted in the landscape. You can plant them in fall or early spring.
If you decide to plant them in the landscape, look for a spot that is well-drained and gets full or partial sun. Mums will likely benefit from the incorporation of some type of appropriately decomposed organic matter into the soil. Optimal plant spacing varies by cultivar, but 18 to 24 inches is commonly recommended. Provide mums with adequate water.
For sufficient nutrition during spring and summer, you can either use a slow-release fertilizer or regularly apply a water-dissolved fertilizer.
A traditional recommendation has been to repeatedly pinch garden mum stems back to about 6 inches in height between spring and early to mid-August to encourage them to branch more and thus produce more flowers. However, many garden mums grown now are no-pinch types that reduce the labor needed to grow them in the greenhouse or nursery. So, you may get satisfactory flowering without a great deal of work.
Mums are daylength sensitive and initiate the formation of flower buds when nights are longer than some threshold (approximately 11 to 12 hours of darkness). We call them short-day rather than long-night plants, even though it’s the length of uninterrupted darkness that’s critical. Plants kept indoors year-round or in a place where an outdoor light occasionally interrupts the darkness may not flower well.
Let me know if you have questions.
Dr. Mary Helen Ferguson is an Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at firstname.lastname@example.org or 985-277-1850 (Hammond) or 985-839-7855 (Franklinton).