Rheum rhabarbarum (garden rhubarb)

Japanese name: ルバーブ
Scientific name: Rheum rhabarbarum

[Overview]
A perennial 1–2 m tall.
It has a thick, short rhizome.
Many leaves arise from the base; they are triangular-ovate, 12–60 cm long and 10–60 cm wide, with wavy margins.
5–7 veins spreading palmately from the leaf base are conspicuous.
The petiole is semicylindrical and hollow, green to red.
A flower stalk 1–2 m tall bears many small yellow-green flowers in a panicle 15–40 cm long.
The fruit is an achene with wings.

[History]
It has been cultivated since Greek and Roman times; it was introduced to England in the 16th century, later spread to Germany and America, and was introduced to Japan in the Meiji era.

[Uses]
The petioles are soft, fragrant and sour, and are eaten raw, stewed, or candied in sugar.
The leaves contain oxalic acid and are therefore not eaten.
The rhizome was used medicinally as a substitute for daio.

[Cultivation]
Propagate from seed or by division.
The suitable growing temperature is 10–25°C, and it has weak heat tolerance, so it is suited to cold regions and cool highlands.
It prefers fertile soil that is sunny and well drained.
It becomes a large plant, so it needs ample space, with a ridge width of 100 cm and a spacing of 45–75 cm or more between plants.
Excess moisture causes root rot, so water only after the soil surface has dried.
Apart from slow-release fertilizer based on nitrogen applied as base fertilizer, no other fertilizing is particularly needed.
Powdery mildew can occur.

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