In the world of flower aristocracy, chrysanthemum is king, at least in the fall season. No perennial garden flower adds more color to the home and garden in fall than the chrysanthemum. Cultivated for millennia, this plant has been developed into a wide range of cultivars which provide almost all colors as well as different flower and plant forms. It is one of the few flowers that begins blooming in late summer and, with the proper choice of cultivars, can continue to add color to the landscape beyond the first frosts of autumn.
The word chrysanthemum is derived from the Greek chrysos (gold) and anthos (blossom). It is the common name given to Dendranthema x grandiflorum. A member of the Asteraceae plant family, until about a decade ago this plant was classified in the genus Chrysanthemum. Hence the origin of its common name. Chrysanthemum is an example of a "cultigen." The latter term is given to plants whose origin or selection is due primarily to human activity, oppose to having developed naturally in the wild.
Genetically, chrysanthemums are hexaploids and possess six sets of chromosomes, instead of the more usual two. This makes them highly sterile and less competitive from the standpoint of establishing populations in the wild. It also helps to explain the differences that exist between various cultivars' ability to thrive under certain environmental conditions. Formerly known as hardy chrysanthemum, this designation has been abandoned (more or less) in favor of garden chrysanthemum because of the varying ability of different cultivars to withstand cold temperatures. Florist chrysanthemum, on the other hand, is a term applied to greenhouse-grown potted or cut mums not considered to be winter hardy.
The first chrysanthemums probably were cultivated in China as many as 2000 years ago. There, it was used for its medicinal value as well as an ornamental plant. The roots of the plant were boiled by people in ancient times to produce a tea used to treat headache. Additionally, young shoots and petals were consumed in salads and the leaves of mums were brewed to produce a festive drink.
Chrysanthemum is a good example of a short-day plant that flowers in response to the length of day versus the length of night. 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. In some areas, the heat and drought of late summer causes a delay in bud development, but as nights cool and water becomes available, additional buds form and flowers normally are produced.
The flower of a chrysanthemum actually is a compound inflorescence consisting of many small flowers (a.k.a. florets). The small florets are of two types: ray and disc. 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.
Garden mums usually come in one of three flower forms: single (daisy), anemone or decorative. Daisy mums have a central mass of disc florets surrounded by a ring of ray florets, giving them the typical daisy-like appearance. There are daisy types with several rings of ray florets which gives them a fuller appearance.
Anemone-flowered mum cultivars have a center of enlarged disc florets which give them a cushioned appearance. Their reproductive structures are hidden; thus, the center does not appear yellow from the anthers as is the case with daisy-flowered types.
Chrysanthemum cultivars bearing flowers with a preponderance of ray florets that totally hide the disc florets are said to have decorative flowers. This flower type is the most popular among garden mums marketed in the fall. Pompon is a type of decorative mum with very short ray florets, making them globe-shaped and small.
The flower size of chrysanthemum ranges from as little as one inch to as large as six or more inches in diameter. Those cultivars normally used in the garden have small flowers which are produced in great abundance. The large-flowered forms, sometimes called football mums and spider mums, are produced as cut flowers and have all of their side buds removed to cause the plant to put all of its energy into the terminal bud. This practice is called "disbudding" and is not performed on garden mums.
There are many different cultivars of garden chrysanthemum from which to choose today. Each year, new cultivars with improved growth habit, flower color and garden performance are added to the list. A relative newcomer to the scene has been the Belgian or European garden chrysanthemums. These cultivars are known for plants with a large, mounded growth habit and lavish display of color. Although individual flowers are smaller than other garden mums, they are borne in great abundance making for a spectacular show in the garden.
Chrysanthemums vary with regard to the length of time required to bloom after exposure to short day lengths. Some garden mums flower as soon as 6.5 weeks following short day exposure, while other might require as many as 9 weeks, or longer, to flower. When cultivars with a longer response are planted into the garden, they often flower late enough that flowers can be adversely affected by cold temperatures. Chrysanthemums are relatively cold hard and light frost normally do not damage their blooms. As temperatures continue to lower and a heavy frost develops, some flower damage (i.e., "petal burn") may develop. Cultivars requiring a long time to flower (normally marketed as late season mums) should be located in a protected part of the landscape and some attempt to protect them during freezing weather should be made.
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. Container-grown chrysanthemums are readily available in the fall to enjoy. Some gardeners choose to treat them as annuals to be removed after they have bloomed. Others opt to establish plants in beds or borders as permanent additions to the landscape.
When the latter is done, it is important to realize that container mums normally are produced in a growing medium very high in organic matter. When these plants are planted into a very heavy clay soil that has not been improved, the difference between the two root environments often prevents good root establishment which can lead to winter kill. Gardeners should make sure the soil around the root ball of the newly transplanted mum has been enriched with an abundant amount of organic matter. Newly set mums also should be mulched to protect their roots and crown the first winter after planting into the garden. Other than amending the soil with a compound high in phosphorus such as bonemeal, do not apply fertilizer in the fall.
Newly-planted mums normally produce some new vegetative growth in the form of green shoots at the base of the plants in late fall. These green shoots should be maintained during the winter. Therefore, when mulching, use a material porous enough to allow some light to penetrate to the green shoots. Straw, pine needles or evergreen boughs provide protection from the wind and rapid temperature changes, but still allow sufficient light to penetrate.
Readers of this article should be warned that growing garden mums can be somewhat addictive. For those who want to discuss their addiction with others, The National Chrysanthemum Society has 35 chapters across the nation. For more information visit the Society's web site at: www.mums.org.
REVISED: October 12, 2021