Euphorbia pulcherrima (poinsettia)

Japanese name: ポインセチア
Scientific name: Euphorbia pulcherrima

[Overview]
An evergreen shrub grown as a foliage plant, reaching 3–5 m in height in its native habitat.
When the stems or leaves are damaged, a milky white latex is exuded.
Leaves are simple and alternate, ovate to elliptical, about 10–15 cm long.
The leaf margin is crenate or has large projections.
At the branch tips the leaves are nearly whorled, and they are colored like petals to form bracts.
The bracts are usually bright red, but come in various colors such as white, yellow and bicolors.
Small flowers are borne in the center of the bracts.
The flowers are held in cup-shaped inflorescences (cyathia) about 7 mm across, enclosed in a green urn-shaped involucre, and have no perianth.
15–25 inflorescences are borne clustered at the stem tips.

[History]
It was introduced to America in 1825 by J. R. Poinsett, the US ambassador to Mexico, and its name also derives from this person.
It then spread through Europe and arrived in Japan in the middle of the Meiji period.

[Cultivation]
Propagate by cuttings.
It prefers fertile soil that is sunny, well drained and moisture-retentive.
In poor light the lower leaves drop.
With poor drainage, the roots may rot in the hot season.
During the growing season from spring to autumn, water when the soil surface dries and apply chemical fertilizer once a month.
In winter keep watering modest, and during flowering apply liquid fertilizer once a week.
In mid-April, cut it back hard, leaving 2–3 nodes from the base of the stem, so that the plant's shape is well balanced afterward.
It is susceptible to cold, so bring it indoors in early autumn when temperatures fall to 15°C or below.
If it is hit directly by heater air, it dries out and the leaves drop.
Because it is a short-day plant, it does not flower and the bracts do not color well unless it receives 12 hours or less of light per day.
Therefore, from late September until the bracts have colored, do not expose it to artificial light at night; from 17:00 every day until morning, cover it with a cardboard box or similar to block the light.
Pests and diseases include the greenhouse whitefly and scale insects.

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