The poinsettia is a commercially important flowering plant species of the diverse spurge family Euphorbiaceae. Indigenous to Mexico and Central America, the poinsettia was first described by Europeans in 1834. It is particularly well known for its red and green foliage and is widely used in Christmas floral displays. It derives its common English name from Joel Roberts Poinsett, the first United States minister to Mexico, who is credited with introducing the plant to the US in the 1820s.
Poinsettias change color in response to shorter winter days. Poinsettia flowers are made up of the bracts, which look like petals, and the tiny yellow flowers in the center, called cyathia. Poinsettia thrives in bright light as a houseplant and also outdoors in partial shade in U.S. Department of Agriculture plant hardiness zones 9 through 11.
Poinsettias are generally shrubs or small trees that can grow quite large in their natural habitat, reaching heights of 10 feet or more. However, when cultivated for ornamental use, they are kept much smaller, usually 2 to 4 feet tall. The most notable characteristics of poinsettias is their colorful bracts, which many people mistake for flowers. These bracts are actually modified leaves that can be red, pink, white, or marbled. The true flowers are the small, yellow structures found in the center of these bracts. The foliage is green, often with a slightly toothed margin, and the leaves are ovate to lanceolate in shape.
The actual flowers of the poinsettia are small, yellow, and clustered together in the center where the bracts converge. They lack petals but have a structure typical of the Euphorbia family, with cyathia (cup-like structures) containing tiny male and female flowers. Poinsettias bloom in response to short days, which in the Northern Hemisphere occurs around late November to January, aligning with the Christmas season. The bracts display their vibrant colors during this period.
Propagating poinsettia is easily done from stem cuttings, which will root in just a few weeks if kept under warm, bright conditions. While not as toxic as once thought, poinsettias can cause mild irritation if ingested or if the sap contacts skin or eyes. They are generally considered safe around pets and children with proper care.
Wild poinsettias occur from Mexico to southern Guatemala, growing on mid-elevation, Pacific-facing slopes. One population in the Mexican state of Guerrero is much further inland, however, and is thought to be the ancestor of most cultivated populations. Wild poinsettia populations are highly fragmented, as their habitat is experiencing largely unregulated deforestation.
Every year in the United States, approximately 70 million poinsettias of many cultivated varieties are sold in a six-week period. Many of these poinsettias are grown by Paul Ecke Ranch, which serves half the worldwide market and 70 percent of the US market.
Cultivation
Light: During the growth phase, poinsettias need bright, indirect light. For the bracts to turn color, they require long nights, ideally 14 hours of uninterrupted darkness for at least 5 consecutive days to initiate blooming.
Temperature: Ideal daytime temperatures are between 65-70°F (18-21°C), and nights should ideally be a bit cooler, around 60-65°F (15-18°C). They are sensitive to cold and should not be exposed to temperatures below 50°F (10°C).
Water: Poinsettias need consistent moisture but should not be overwatered. Allow the surface of the soil to dry out slightly between waterings. Watering should be done with room temperature water, and it’s advisable to use pots with drainage holes to prevent root rot.
Soil: Well-draining soil is crucial. A mix designed for houseplants or even a cactus mix with added peat moss for moisture retention works well.
Fertilization: During the growing season (spring and summer), feed with a balanced, all-purpose fertilizer every two weeks. Reduce or stop fertilization during the blooming period and in the fall when they are preparing for their color change.
Pruning: After the blooming period, around late winter or early spring, poinsettias can be cut back to about 4-6 inches from the soil line to encourage new growth. Pinching back new growth in spring and summer promotes bushiness.
Repotting: Repot in spring if the plant has outgrown its pot or if the soil has become depleted. Choose a slightly larger pot to give roots room to expand.
Post-Bloom Care: After the holiday season, with proper care, poinsettias can be kept year-round. They require a period of darkness in autumn to rebloom, which can be simulated indoors by covering the plant or placing it in a dark room for 14 hours each day.
Special Notes
- Day-Length Sensitivity: The most critical aspect for blooming is managing the plant’s exposure to light in the late fall. Even brief exposure to light during the required dark period can interrupt bract coloration.
- Cultural Significance: Poinsettias are strongly associated with Christmas and are one of the most common holiday plants in the U.S. and Europe. They have historical and cultural significance in Mexico, where they are known as “Flor de Nochebuena” (Christmas Eve Flower).
How to Grow Poinsettias in a Greenhouse
Growing them in a greenhouse is the best way to ensure healthy and bushy poinsettia plants.
- Prepare a container full of well-draining potting mix. Add organic matter, like peat moss, to the container using a hand trowel. The organic matter adds nutrients and water absorption abilities to the substrate.
- Place your young poinsettia plant into the container during the spring or summer. Cover the root system completely with the potting mix using a hand trowel. The poinsettia should already have a sturdy root system and strong upper branches if grown from a cutting.
- Water the poinsettia with a watering can until the water slightly leaks from the container’s drain holes. Periodically check the soil’s surface for dryness; poinsettias need moist soil for the best growth.
- Place the poinsettia in the greenhouse near a south-facing wall. Allow it to receive full sunlight until the end of September.
- Cover the poinsettia with a cardboard box for 14 hours each night after the beginning of October. Do not let the box touch the foliage.
- Set the greenhouse nightly temperature between 60 and 70 degrees Fahrenheit. The combination of light and temperature help the plant flower and create its signature red hue.
- Continue to cover the plant nightly for the next 10 weeks.
- Set the flowering poinsettia on a patio or display it indoors during the December holidays. The natural short and cool days allows the poinsettia to remain bright red for several weeks after blooming.
How to Propagate Poinsettia Cuttings
- Growing poinsettia from cuttings is best done in the summer after the plant begins to produce new shoots at the base. Wait until the shoots reach 3 to 5 inches long before using them as cuttings to ensure they are mature enough to put down roots.
- Fill a clean, dry 4-inch plastic pot with sterile medium, such as a coarse sand or a mixture of half sand and half peat.
- Sever a 2 1/2- to 4-inch-long stem from the base of the poinsettia using thoroughly cleaned, sharpened pruning shears. When propagating poinsettia, choose a cutting with a pliant stem and several small leaves at the tip.
- Strip off the lowest leaf to expose the growth node. Dust the end of the cutting with 0.2-percent IBA rooting hormone. Poinsettia cuttings will root without pretreatment, although rooting hormone will hasten the process and produce more roots.
- Insert the severed end of the poinsettia cutting into the moistened growing medium. Press it in until the bottom one-third is buried. Gently press the medium against the stem.
- Cover the pot with a propagation dome or a large, clear plastic bag held up with wooden skewers. Set the pot inside a lightly shaded cold frame or indoors, near an east-facing window.
- Mist the poinsettia cutting every day to keep the leaves hydrated and cool. Check the moisture content of the growing medium each time you mist the cutting. Water to a 3-inch depth if the growing medium feels barely damp in the top 1 inch.
- Check for roots in two to three weeks by gently tugging on the base of the cutting. Feel if it is “stuck” to the growing medium by roots. Remove the propagation dome and propagation mat once the cutting roots.
- Transplant the poinsettia cutting into a 6-inch pot filled with standard potting soil two weeks after it roots. Grow the poinsettia under extremely bright, moderately humid conditions indoors or out. Provide 1 inch of water each week.