Figure 1. The poinsettia (Euphorbia pulcherrima).

Introduction

The poinsettia (Euphorbia pulcherrima) is the traditional Christmas plant. It is native to Mexico and Central America where it can be found growing as a large shrub or small tree to 10-12’ tall at maturity. This species was introduced to the United States in the early 19th century by Joel Poinsett, the first U.S. Ambassador to Mexico. In mild climates, such as Florida and California, the poinsettia is also grown in the landscape.
 
The striking beauty of the poinsettia is found in the showy bracts, which are specialized leaves, surrounding the true yellow to yellowish-green flowers. Plants with red bracts are most popular, but plants with yellow, orange, pink, white, cream and speckled or marbled bracts are also available. Consumers who desire other colors can purchase spray-painted poinsettias, sometimes with added glitter on the bracts. Color can be further enhanced by asking the florist to wrap your plant in floral foil with a color of your choosing. However, be sure there are holes at the bottom of the foil to facilitate proper drainage. Over 150 varieties have been bred to date as well, and the consumer is now able to choose very dwarf and compact plants (referred to as mini poinsettia or sometimes Princettia) to tall tree poinsettias that have been trained to grow tall with one main trunk up to 3’ tall, then topped with a rounded head of poinsettia foliage and bracts. Lastly, consumers can also purchase poinsettia hanging baskets in varying sizes. Like many of the hanging basket types. Poinsettias are often sold in multiple plants per container to provide a fuller, more dramatic appearance.

The newer cultivars of poinsettia, in addition to being very showy, have excellent keeping quality and stronger stems than older cultivars. When buying your poinsettia, choose a plant with well-expanded, well-colored bracts. Foliage should be medium to dark green with uniform coloring. Flowers should be present in the center of the bracts, but ideally still mainly closed with little pollen present, with these two points indicating a plant with a longer ornamental shelf life.

Figure 2. Poinsettia leaf variation.

Care

After you purchase your plant, do not expose it to chilling temperatures or cold drafts. If the temperature outdoors is below 50 degrees Fahrenheit, do not carry an unwrapped plant from the retail shop to your car. Poinsettias may suffer chill injury, which can result in partially defoliated bracts and foliage. In the home or other place of display, avoid cold drafts and excessive heat from heating ducts or large incandescent lamps. Temperatures of 70 degrees Fahrenheit or below (down to 60 degrees Fahrenheit) are desirable to retain the best bract color. Large plants can be placed on the floor if light is adequate. Do not allow plants to contact windows, as cold glass may be injurious.

Light plays an important role in the retention of leaves on the plant. Place the plant in an area where it receives at least six to eight hours of direct natural or artificial light. A minimum of 75-foot candles is desirable where possible. This would be similar to the minimum light intensity required for good desk lighting in an office. Incandescent lights, such as those found in most homes, will give a truer, brighter bract color than most types of fluorescent light.

Poinsettias can be displayed with other houseplants. The adjacent plants raise humidity, helping poinsettias last longer. Also, the regular houseplants can be spruced up for the holidays.

Many commercial growers use non-soil mixes of sphagnum peat, pine bark, vermiculite, perlite or similar ingredients. When plants are grown in such non-soil mixes, it is sometimes difficult to decide when the plant needs water. If there is no heavy component (sand or soil) in the mix and a plastic pot is used, the pot can be lifted to determine its weight. If the plant is heavy, there is usually plenty of moisture in the pot; if it is lightweight, the medium is dry, and a thorough watering should be given. Moisture needs can also be assessed by feeling the growing medium in the pot. Water when the top of the growing medium starts to feel dry, but do not allow it to dry out too much. Slight wilting of the plant is not harmful, but avoid severe wilting, which will cause leaves and bracts to drop faster.

Water the plant thoroughly. Make sure a small amount of water drips through the drainage holes of the container. If the plant is wrapped with decorative foil, punch a hole in the foil beneath the pot to allow excess water to escape. The plant should be placed on a saucer to prevent damage to the furniture or flooring.

Do not water the plant too frequently when the soil or growing mix is already wet or this may result in roots suffocating from lack of oxygen, causing the leaves to wilt, yellow and drop, often as a result of root rot disease(s). A carefully chosen plant should remain attractive in the house for a minimum of eight weeks but often into the spring when consumers pay careful attention to temperature, light and moisture needs. Research, originating out of The Ohio State University during the 1970s, showed that poinsettias are not poisonous, but the plants are still intended solely for ornamental purposes. Some people are allergic to the milky sap and may develop a rash when physically exposed to the sap. Avoid breaking the leaves and stems, as this will release the sap. Furthermore, children and pets have been reported to have gastrointestinal issues on occasion when consuming foliage and bracts. It is always wise to keep any houseplant, including poinsettia, out of the reach of small children and pets.

Re-Flowering for Next Year

It is easier to discard a poinsettia plant after the bracts fall and buy a new one next year. Most consumers get busy and often fail to meet the requirements needed to realize a showy plant for the next holiday season. Commercial growers work hard to produce high-quality plants for the public at a reasonable price, given their longevity indoors when properly cared for. The newer cultivars usually hold their flowers (bracts) for several months instead of just a few days or weeks. If light is lacking, the leaves usually drop before the bracts. Adequate light results in longer leaf and bract retention. After the bracts have faded and the plant is no longer attractive, watering frequency can be reduced, and the plant should be held in a cool location, such as 50 degrees to 60 degrees Fahrenheit. However, if the foliage is still attractive, grow the plant as a foliage plant.

In March or April, cut back the original stems to within four to six inches of the soil surface. If the plant is too large for the pot, shift to a larger container using a good potting mixture from a local florist, greenhouse, nursery or garden center. If the original pot contained more than one plant, these can be separated and planted in individual pots if desired.

About May 15, well after the danger of frost is past, and when nighttime temperatures do not dip below 50-55 degrees Fahrenheit, the plant can be moved outdoors to a partially shaded (not heavy shade) area of the flower garden or shrub border and the pot placed in the ground to the rim. Ideally, the plant will receive strong morning sunlight. The soil in the area should be well-drained to prevent overwatering and poor drainage. A large heavy pot will not need to be buried to the rim.

If a well-lit, moderate-temperature location is available where the plant can be cared for, it can be kept inside most of the time. However, plants benefit from some outside exposure. A soft summer rain shower can really perk up a plant. However, do not place plants where hot, drying winds and reflective heat can cause damage.

Water as needed, avoid extremes of underwatering or overwatering. Apply a complete houseplant fertilizer throughout the summer at the rate and frequency recommended by the manufacturer. Occasionally lift the pot and prune of roots that have grown into the soil. If this is not done, excessive root growth into the soil may make it more difficult to move the plant indoors later. Between July 15 and Aug. 15, long shoots will develop. The terminal portions of these shoots should be cut off to induce branching. These excised tips, three to five inches long, can be used for cuttings if additional young plants are desired. Take the cuttings in the early morning, dip the basal ends in a rooting powder (rooting hormone) and plant in a pot or polystyrene cup (punch drainage holes in the bottom) filled with moist vermiculite or one-half sphagnum peat and one-half vermiculite or perlite. Cover with plastic film and place in a shady, warm location. Keep moist but gradually aerate by cutting holes in the plastic film and, when cuttings are rooted (three to five weeks), transplant to larger pots.

If no new cuttings are taken in the summer, and your interest is only in re-flowering the original plant, keep the tips of the longer shoots pinched back to induce branching. Try to shape the plant into a rounded, bushy plant, making the last pinches approximately Aug. 15 to Aug. 25. If too many shoots result, carefully prune of a few excess branches. Plants can be transplanted into a larger container if they appear to be outgrowing their current pot. If the plants appear to be in proportion to the pot, leave them alone.

Lift the pots from the flower garden or shrub border in late September. Bring the plants inside and place them in a sunny window. Avoid “burning” light, but do not give too much shade or leaf drop, spindly growth and sparse blooming may result. Follow the previously mentioned watering practices.

Use a houseplant fertilizer during this indoor forcing period, following the manufacturer’s recommendations relative to rate and frequency. Do not apply more fertilizer than recommended.

Poinsettias must have long, uninterrupted nights to bloom, and for the plants to flower for Christmas, they should be kept in complete darkness from 5 p.m. to 8 a.m. each night (sometimes less but follow the hours above to be on the safe side), beginning in late September, placing them back in the sunny window each day. This can be as simple as placing the plant in a lightproof box or a closet every evening. Just turning on a closet light for a moment, headlights shining through a window or any other source of light contamination may disrupt flowering. Follow this light-free schedule until good bract color appears (often prior to Thanksgiving). If possible, the temperature should remain between 60 to 70 degrees Fahrenheit. Whether you prefer trying to re-flower your poinsettia or purchasing another one the following winter holiday season, enjoy the poinsettia’s faming beauty each year. This living symbol of a joyous season is a colorful part of the American Christmas tradition, as well as in many other parts of the world, particularly throughout Europe.