Green Thumb – Colorful Chrysanthemums

Posted: August 20, 2021
Chrysanthemum is Japanese,
She’s a fine lady, if you please.
She comes to see us once a year,
about the time Thanksgiving’s here.
— Elizabeth Gordon

By late summer, the petunias get spindly, the coneflowers get floppy, and the phlox come down with mildew. That’s when chrysanthemums come to our rescue, revving up our enthusiasm with mounds of colorful flowers. 

Mums were first cultivated in China more than 3,500 years ago. Only the nobility could grow them. Their seeds arrived in Japan around the fourth century, where the flower became the symbol of the emperor. Now they are the most popular flower in the world after the rose.

Plant breeders have done tremendous work creating thousands of varieties with interesting petal shapes, colors and sizes. The flowers range in size from one to six inches across, and the plants can stand six inches to three feet tall. There are pompons, daisies, buttons, and showy football types. The petals can be spikey, spoon-like, or quilled, and curve under, over, or lay flat. 

There is a temptation to buy mums in the fall, enjoy them in their pots, and then plant them in the ground after they bloom out. This doesn’t work because it is too late for them to get established. The mums you buy at that time should be treated as annuals.

The best time to plant mums is in the spring or early summer. Purchase them as small potted plants, or order them from garden catalogs. Mums have shallow, fibrous roots that need as much time as possible to get established before winter. Give them some growing space because they can get powdery mildew. Water them well during hot, dry summer weather. They like fertile, well-drained soil and at least 6 hours of sun a day.

Don’t apply additional fertilizer until the next spring. Then, use a complete fertilizer, such as 10-10-10 one to three times during the active growing season. Stop fertilizing them when flower buds develop.

Chrysanthemums develop their flowers as the days get shorter in late summer.  Different cultivars require different periods of darkness. This means that with careful selection your garden could have mums blooming from August through October.

If you want your mums to produce many flowers, they need to be pinched. To do this remove about one inch off the tip of each shoot by snapping or cutting it off. Leave two to three leaves on the shoot. The first pinch is done when the plants are about six  inches tall. Then, pinch again on all the shoots every six or so inches to promote bushy, compact plants with many flowers. Stop this process by July 4.

After they bloom, trim off the dead flowers. Then, once the ground freezes, cut down the dead stems and place them on top of the plant crowns. Mulch them with six to eight inches of shredded leaves, straw, or evergreen boughs. Mulching is necessary to improve their winter survival by protecting their roots. Remove the mulch in early spring when new growth appears.

Divide your mums in the spring every three to five years when new growth appears in the spring. Dig up each plant and separate the outer pieces from the center with a sharp tool.  Discard the original center and replant the separated outer pieces.  Three to five shoots are enough to start a new clump.

Each fall we can look forward to the exciting show of color provided by chrysanthemums. They look sensational planted in groups of three to five plants and with asters or ornamental grasses.

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener

The Master Gardener Help Desk is open. Garden questions can be emailed to uiemg-dekalb@illinois.edu, or call 815-758-8194, Mon. – Fri., 9 a.m. – noon.

Photos courtesy of Janice Weber


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