The poinsettia, formally known as Euphorbia pulcherrima, is a popular seasonal plant. This species is actually a perennial shrub native to the tropical deciduous forests of Mexico and Central America. Because it originates in a warm climate, the poinsettia requires consistent warmth and protection from cold to thrive. For most people outside of subtropical regions, this means the plant must be treated as an indoor houseplant.
Essential Indoor Care
Maintaining the poinsettia indoors requires balancing temperature, light, and moisture to simulate its native warm habitat. The plant prefers consistent temperatures, ideally staying between 65 and 75 degrees Fahrenheit during the day. Stable temperatures are important, as fluctuations can cause the colorful bracts and leaves to drop prematurely.
Poinsettias are highly sensitive to drafts and should be kept away from cold windows, exterior doors, and heating vents. Even brief exposure to a cold draft can inflict damage. They need bright, indirect light for about six hours daily to maintain the color of their modified leaves. Direct, intense sunlight causes colors to fade, so a spot near a south, east, or west-facing window is appropriate.
Proper watering is crucial, as poinsettias suffer quickly from both over- and underwatering. The soil should be kept consistently moist but never saturated, meaning you should water only when the surface feels dry to the touch. Ensure the pot has adequate drainage and that the plant is not left sitting in water, especially if wrapped in decorative foil. Excess water must be poured out to prevent root rot.
Guidelines for Outdoor Placement
Poinsettias can only survive outside year-round in climates that mirror their tropical origins. They are considered hardy only within USDA Hardiness Zones 9 through 11, which includes limited parts of the United States. In these frost-free regions, they can mature into large, woody shrubs up to 10 feet tall.
In cooler regions, the plant may be moved outdoors seasonally, but only after the danger of frost has passed, typically in late spring or early summer. Poinsettias are intolerant of cold; temperatures below 50 degrees Fahrenheit cause the leaves to drop. The plant must be brought back inside before autumn’s first cold snap, generally when nighttime temperatures consistently fall below 60 degrees Fahrenheit.
When placed outside for the summer, the plant prefers filtered light or bright shade, protected from intense afternoon heat. They are understory plants in their native habitat, appreciating light that is bright but diffused. If moving the plant outdoors, repotting it into a larger container in the spring allows for robust growth throughout the warmer months.
Manipulating the Environment for Color
Encouraging the poinsettia’s modified leaves, known as bracts, to regain vibrant color requires precise manipulation of light exposure. This depends on photoperiodism, the biological response to the relative lengths of light and dark periods. Poinsettias are “short-day” plants, requiring a long, uninterrupted period of darkness each night to initiate color change.
To achieve the desired color in time for the winter holidays, a strict schedule must be implemented starting around early October. The plant requires a minimum of 14 consecutive hours of complete darkness every night for eight to ten weeks. Even a brief flash of light from a streetlight or nearby lamp can disrupt this process and delay color formation.
During the remaining ten hours of the day, the poinsettia must be returned to a location where it can receive bright, indirect light. Throughout this schedule, the temperature should be maintained between 60 and 70 degrees Fahrenheit. This cycle of long, uninterrupted darkness followed by bright light must be maintained daily until the bracts show definite color, typically by early December.