Poinsettia

Identification and origin

Euphorbia pulcherrima belongs to the spurge family, Euphorbiaceae. It is native to Mexico and Guatemala, where it grows along the coast and in dry tropical forests. In the wild it is a deciduous to semi-evergreen shrub that can reach 10 ft tall and 8 ft wide. In a pot it rarely exceeds 2–3 ft.

The dark green, oval leaves are 3–6 in long; their edges can be smooth, lobed, or bluntly toothed. Stems and leaves release a milky white sap as soon as they are cut or torn.

What look like petals are bracts, that is, modified leaves that take on color. The true flowers are tiny: small yellow clusters called cyathia gathered in the center, each with a conspicuous yellow gland. Breeding has tightened those cyathia and broadened the bracts, which now come in red, pink, white, peach, yellow, marbled, or speckled forms. Red still accounts for the bulk of sales; ‘Prestige’, whose sturdy branches are less likely to snap, is one of the best-selling reds. You will also find ‘Alaska’ with frosty white bracts, ‘Sky Star’ with crimson bracts dotted with white, ‘Christmas Mouse’ with small rounded bracts, and ‘Tapestry’ with yellow-variegated leaves.

The plant takes its common name from Joel Roberts Poinsett, the first U.S. ambassador to Mexico, who introduced it to Philadelphia in 1828. The epithet pulcherrima refers to beauty in Latin.

When buying, choose a plant leafy all the way to the base, with stiff stems and with the little yellow flowers in the center not yet open.

Light

Indoors, put it in your brightest room, where it gets at least six hours of bright light a day. Direct sun can fade the bracts: behind very sunny glass, filter the light with a sheer curtain. Too little light can cause leaf drop.

After the color fades and it becomes a green plant again, move it close to a sunny window. If it spends the warm season outdoors, four to five hours of sun a day suit it, ideally with some shade during the hottest hours.

Watering

Poinsettias like moderately moist potting mix. Feel the surface: when it is dry, water thoroughly until water runs out of the drainage hole, so the whole root ball is moistened. Never let the mix dry out completely, but never let the pot sit in water either: excess water rots the roots and the base of the stem.

The classic trap is the decorative pot cover that holds water. Take the plant out of its cover to water it, let it drain, then put it back. The state of the potting mix decides, never the calendar.

Potting mix

It needs a well-drained mix rich in organic matter, such as a blend of loam, compost or leaf mold, and peat moss. The pot must have drainage holes.

Do not fertilize while it is in color. Afterward, from spring through fall, feed every two to three weeks with a balanced complete fertilizer.

Temperature

The plant is comfortable at 64–70 °F. While it is in color, daytime temperatures should not exceed 70 °F: too much heat makes leaves yellow and drop and fades the bracts early. On the other hand, below 50 °F chilling injury causes premature leaf drop. Keep it away from heaters, fireplaces, vents, and cold air currents.

It can spend the warm season outdoors once nights stay above 50 °F; bring it indoors to a sunny spot when nights cool to 55–61 °F. Protect the bracts from wind and cold rain. In the ground it can only be grown in mild climates, in USDA zones 9 to 11.

Repotting

At the start of summer, move it to a pot 2–4 in wider than the previous one, using a mix rich in organic matter. Handle it gently: its stems are very brittle.

Pruning

In spring, once the bracts have lost their color, cut the stems back to about 8 in tall. New shoots will grow from the nodes. Through the summer, pinch the shoot tips or shorten the branches for a bushier, fuller plant. Stop pinching at the end of summer, or you will remove the coming bracts.

Propagation

Stem cuttings are taken at the start of summer. Cut the tip of a healthy shoot, dip the base in rooting hormone, and insert it in a light mix of peat moss, perlite, and vermiculite. Wear gloves: the sap is irritating.

Bringing a poinsettia back into color.

It is a short-day plant: its bracts color only after a long run of nights with no light at all. From the start of fall, for eight to ten weeks, give it at least 14 hours of total, uninterrupted darkness every night (a closet or a large box), then six to eight hours of bright light during the day, with nights around 61 °F. Depending on the cultivar, the bracts color up at the start of winter. It takes discipline and a healthy plant.

Common problems

• Leaf drop: cold below 50 °F, air currents, poor light, poor nutrition, or the opposite, too much heat.
• Yellow leaves and bracts that fade quickly: excess heat, or hot, dry air near a heating appliance.
• Wilting even though the mix is moist: root rot from overwatering or from a pot cover full of water.
• Broken stems: brittle wood that must be handled carefully.
• No new colored bracts: nights not long enough or interrupted by light, or pinching done too late.
• Pests: whitefly is the most common; also watch for mealybugs, soft scales, and spider mites.

The same symptom can have several causes: look at light, temperature, watering, and the roots together before drawing conclusions.

Toxicity

Poinsettia is listed as toxic to dogs, cats, and horses, though its toxicity is generally overrated. The sap irritates the mouth and stomach and can cause vomiting. In people the severity is low: a significant amount would have to be eaten to cause a mild stomachache, sometimes with diarrhea or vomiting. The sap, which contains diterpene esters, can however cause contact dermatitis, reactions in people with latex allergies, and eye irritation. Wear gloves when pruning, wash skin with soap and water, and flush eyes well with water after contact; if a pet eats it, contact a veterinarian.