Plant Profile: The Poinsettia

Perhaps no plant has as stronger connection to the holiday season than the poinsettia. The brightly colored shrub has been a feature of Garden floral shows for more than a century, and is the central theme for the 2017 Gardenland Express Holiday Flower and Train Show.

What is a poinsettia?

The poinsettia, Euphorbia pulcherrima, is a member of Euphorbiaceae, the spurge family. Euphorbiaceae is a large and highly diverse family that includes trees, shrubs, herbaceous plants and succulents. Missouri Botanical Garden taxonomist Dr. Gordon McPherson studies Euphorbiaceae and published six new species in 2017.

Poinsettias are prized during the holiday season for their large, colorful “flowers,” but what appear to be red or white petals are actually bracts, or modified leaves. Like other members of Euphorbiaceae, poinsettia flowers are unisexual, meaning that they only contain male or female parts. These tiny flowers are clustered together into a group called a cyathium, which mimics a single bisexual flower.

The poinsettia is named for Joel Roberts Poinsett, our country’s first ambassador to Mexico. Poinsett brought the plants to the U.S. in the 1820s. The scientific name, Euphorbia pulcherrima, means “very beautiful.”

Poinsettia_Euphorbia_'Eckecory'_DULCE ROSA3_130313_INCR
Poinsettia ‘Dulce Rosa’ variety. Photo by Tom Incrocci.

Poinsettias are native to the low and mid-elevation tropical deciduous forest of southern Mexico. Wild poinsettias grow as small trees or tall flowering shrubs. Since these are tropical plants, poinsettias are very frost tender. In northern climates, even brief exposure to freezing temperatures, such as a walk from the store to the car, can damage leaves.

Poinsettias are the most widely grown of all shrubby euphorbias with over 100 varieties available on the market. They represent about 85 percent of potted plant holiday season sales. The U.S. exports about 90 percent of the world’s poinsettias, which are grown commercially in greenhouses in all 50 states, producing over 60 million plants for sale. With the proper maintenance and care, these plants can last year-round.

Are Poinsettias Poisonous?

Unlike many members of Euphorbia, the milky sap within poinsettia leaves and bracts is not lethally toxic. Although some people or pets may experience upset stomachs if they ingest the sap, this often does not require a visit to the doctor. In fact, research shows that a person would need to eat hundreds, possibly thousands of poinsettia leaves (about 500 leaves for every 50 pounds) to receive a toxic dose of the latex sap. There may even be some medicinal qualities within the sap of a poinsettia. It is documented that parts of the poinsettia were used by the Aztecs to produce medicine and dye.

Producing Poinsettias at the Garden

The Garden produces nearly one thousand poinsettias each year in our production greenhouses. Poinsettias are grown according to the number of plants requested based on the design by the floral display supervisor. The number of poinsettias is approved by January 1, giving Greenhouse staff six months to prepare the greenhouses and order poinsettias for the show.

Before the poinsettia stems and pinch plants arrive, Greenhouse staff spend a week cleaning and sterilizing the designated greenhouse, tools, and pots to prevent diseases and pests from damaging the new crop. Single stem cuttings come into the Greenhouse around the 4th of July. The second shipment of pinched plants arrives two weeks after. Throughout their growth, the poinsettias are placed on an integrated pest management (IPM) program. A combination of beneficial insects, such as parasitic wasps, and biopesticides is used to reduce pests and prevent outbreaks.

The poinsettias are set on a strict schedule from the day they arrive to when they are placed in the show. The greenhouse is kept at 75 degrees during the day and 67 degrees at night. First, Greenhouse staff focus on promoting strong root growth. Once poinsettias are rooted, Greenhouse staff fertilize the plants to promote vegetative growth. Vegetative growth occurs until late October, then staff begin to pinch off the top of the plants to encourage lateral branching.

To promote coloring of bracts, poinsettias need 12 hours of full darkness. All lights within and around the poinsettias’ greenhouse must be turned off at night starting in mid-September. Color begins to show in the bracts around Halloween. The poinsettias come in all different shades of red, white, pink, and orange.

The Greenhouse produces around one thousand poinsettias behind-the-scenes. Most go in the Gardenland Express. Some are held back as replacements. Others are used in displays in Center for Home Gardening, Linnean House, and Temperate House.

Poinsettia display 2005
Poinsettias of various colors on display during the Gardenland Express Holiday Flower and Train Show in 2005.

History of Poinsettia Displays at the Garden

The Garden has been showcasing poinsettias for more than a century. The original Floral Display House opened in 1915, and hosted an annual poinsettia show until the 1970s. The plant was also used prominently for holiday displays in the Climatron. The poinsettia is now an integral part of the Gardenland Express Holiday Flower and Train show in the Orthwein Floral Display Hall.

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Jennifer Laquet, Interpretation Specialist

Cassidy Moody, Digital Media Specialist

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