Ipomoea alba (tropical white, "Yorugao")

Japanese name: ヨルガオ （夜顔）
Scientific name: Ipomoea alba

[Overview]
A climbing perennial.
Because it is sensitive to cold, it is treated as an annual in Japan.
The vines grow to several meters and twine around other objects.
The vines have hooked, spiny projections, but they do not hurt when touched.
The leaves are alternate, ovate to round, 5–15 cm long, with a heart-shaped base, sometimes 3-lobed, and abruptly pointed at the tip.
The leaf margin is entire.
The petiole is 5–20 cm long.
The flowers are borne singly or several together in the leaf axils and open at night; they are funnel-shaped, 8–14 cm across, white, and fragrant.
The stamens and style protrude slightly from the corolla.
The fruit is an ovoid capsule that hangs downward and is hairless; the fruit stalk thickens toward the tip.

[History]
It was introduced to Japan in the early Meiji era.

[Cultivation]
Propagate from seed.
Seeds do not germinate at low temperatures, so sow them in May–June, when the temperature rises above 20°C.
The seed coat is hard, so nick the surface slightly with a cutter or similar and soak the seeds in water for a day and a night; this helps the cotyledons open.
Take care not to make the cut too deep.
It prefers sunny, well-drained, fertile soil.
For potted plants, water thoroughly when the soil surface dries; for plants in the ground, rainfall is sufficient.
Apply base fertilizer, and during the growing season place slow-release fertilizer on the soil once every 2 months or give liquid fertilizer about once every 10 days.
Fertilizer high in nitrogen produces only leaves and makes flowering difficult.
Because it flowers as the days shorten, light from outdoor lamps at night can make it less likely to bloom.
Pests and diseases include aphids and spider mites.

[Notes]
It is often confused with Yugao of the Cucurbitaceae, from which kanpyo (dried gourd strips) is made.

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