Oenothera glazioviana (large-flowered evening-primrose, "Omatsuyoigusa")

Japanese name: オオマツヨイグサ （大待宵草）
Scientific name: Oenothera glazioviana

[Overview]
A biennial 50–150 cm tall, found on coastal sandy ground, waste land, river beds and similar places.
The stem is erect and densely covered with spreading stiff hairs; the bases of the hairs are swollen and red, and where the hairs fall off they leave red dots.
Glandular hairs are also mixed in on the upper part of the stem.
There are basal leaves and leaves on the stem; the basal leaves have petioles and rounded tips.
The stem leaves are simple and alternate, elliptic to lanceolate, 5–15 cm long and 2.5–4 cm wide, with a wrinkled, wavy surface and low wavy teeth on the margin.
The flowers are borne in a spike at the stem tip and are yellow, 4-petaled, about 4–8 cm across.
The flowers open from evening and wither the next day.
The calyx is tinged with red.
The fruit is a lanceolate capsule 2–3.5 cm long, densely covered with spreading stiff hairs; the bases of the hairs are swollen and red, and where the hairs fall off they leave red dots.

[History]
It is said to be a plant of hybrid origin that arose in Europe, and it arrived in Japan in the early Meiji period.

[Cultivation]
Propagate from seed.
It dislikes being transplanted, so sow directly where it will grow, or sow in pots and transplant while the seedlings are young.
It prefers sunny, well-drained soil.
For potted plants, water thoroughly when the soil surface dries; for plants in the ground, rainfall is sufficient unless summer brings a long sunny spell and the soil becomes severely dry.
Too much fertilizer produces only leaves, so use it sparingly; for potted plants, in addition to base fertilizer, place a small amount of slow-release fertilizer on the soil in spring.
Plants in the ground need no particular fertilizing.
There are no particular pests or diseases.

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