Garden Chrysanthemums

As summer wanes and most garden flowers show the effects of having endured a season of high temperatures, insects, diseases and other woes, gardeners look forward to a renewal of color in the form of fall-blooming plants. Perhaps no other plant exemplifies this rebirth of color in the fall than the garden (or hardy) chrysanthemum. Available in a myriad of colors and flower types garden chrysanthemums help to extend the beauty of a garden well into the fall.

Chrysanthemum (or mum) is the common name given to Dentranthema x grandiflorum. Chrysanthemum is an example of a cultigen, or a plant that appears to have originated through human intervention rather than in nature. Genetically, chrysanthemums are hexaploids and contain six sets of chromosome instead of the ordinary 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 cultivars relative to their ability to thrive under certain environmental conditions.

The first chrysanthemums probably were cultivated in China as many as 2000 years ago. There it was used for its ornamental as well as medicinal value. The roots of the plant were boiled 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.

From China, chrysanthemum migrated to Japan around the 8th century A.D. where it quickly captured the fancy of the Japanese people. Their fondness of it caused them to adopt a single flowered chrysanthemum as the crest and official seal of the Emperor. Prominent Japanese families also included it on their family crests, and one of the highest orders of chivalry in Japan is the Imperial Order of the Chrysanthemum. The people of Japan observe a National Chrysanthemum Day which is called locally the Festival of Happiness.

Modern chrysanthemum would hardly be recognized by ancient growers since most cultivars today are much showier than the single daisies that were first grown in the Orient. Chrysanthemum is a member of the Asteraceae (Composite) family whose members bear a compound inflorescence known as a head which bear two types of florets: ray and disc. Ray florets typically are quite showy whereas disk florets are smaller and, oft-times, inconspicuous. The National Chrysanthemum Society divides flowers into 13 different classes. The following are some of the more flower types of garden chrysanthemums:

Decorative: Flattened bloom with short ray florets (petals).
Pompon: Small, globular bloom somewhat flat when young but fully round at maturity.
Single and Semi-Double: Daisy-like bloom with a center "eye" of disk florets and one (single types) or more than one (semi-double types) rows of ray florets.

Garden chrysanthemums are available in the spring as rooted cuttings established in small containers or during the fall as large, mature plants in or near full bloom. Select a planting site that is well-drained and receives at least eight hours of sun. Spring-planted garden chrysanthemums should be planted away from stray light that would prevent them from blooming the following fall. When planting smaller plants in the spring, be sure to space them far enough apart to allow for the future growth and development of the plant. For most cultivars this would be between 18 and 24 inches between plants; spacing 30 to 36 inches apart is preferred for more vigorous cultivars. Apply a granular fertilizer such as 5-10-5 (or equivalent) at the rate of two or three pounds per 100 square feet of surface area and incorporate it into the soil. A soluble starter fertilizer high in phosphorus (e.g., 15-30-15) applied immediately following transplanting also is beneficial.

Spring planted garden chrysanthemums should be pinched at regular intervals (every three to four weeks) to promote bushy, compact growth and more flowers. With most cultivars, the last pinch should be made no later than mid- to late July. As with other garden plants, garden chrysanthemums require about an inch and a half of water per week during the growing season. Mulching plants with materials such as bark, wood chips or other organic materials will help to conserve moisture and also control weeds. Fortunately, garden chrysanthemums are relatively insect and disease free. Aphids, two-spotted mite and powdery mildew are the three main pest problems.

An alternative to planting garden chrysanthemums in the spring is to purchase mature, blooming plants in large containers which are readily available beginning late August to early September. Select plants that are just starting to show color for greatest longevity. It is important to remember that all of the roots nourishing the mature plant immediately after transplanting are contained in the potting medium, which tends to dry faster than normal garden soil.

Although many cultivars of garden chrysanthemums will overwinter in our area most gardeners grow our modern cultivars as annuals. For those wishing to treat them as perennials, cutting back the foliage after it has died and applying a think layer of protective mulch can be helpful.

There are scores of different cultivars of garden chrysanthemums 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 Belgium or European garden chrysanthemums. These cultivars are known for their spectacular size and display of color. Although individual flowers are smaller than normal, they are borne in profusion making for quite a show in the garden.

Readers should be warned that growing garden chrysanthemums can be somewhat addictive. They are easy to grow, available in a wide array of flower types and colors and extend garden color well into the fall. 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.

Dave Trinklein
Horticulture
573-882-9631