Rheum x cultorum

Thorsrud & Reisaeter

Polygonaceae Edible: Flowers, Stem Potential hazards — see below

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Summary

A perennial hybrid rhubarb reaching 1.5 m tall, hardy to UK zone 3. Foliage emerges in February and persists through October, with wind-pollinated flowers appearing in June and seeds ripening July to August. Grows as a hermaphrodite plant in medium to heavy loamy or clay soils with good drainage, tolerating mildly acid to basic pH. Prefers moist conditions and grows in semi-shade to full sun.

Description

Edible Uses

The leaf stem can be eaten raw or cooked. It has an acid taste and is commonly used as a fruit substitute in spring — typically stewed with sugar for use in pies, jams, and similar preparations. Juice strained from stewed rhubarb can also add colour and flavour to a fruit punch. Large quantities of the stems are best avoided due to their oxalic acid content. Immature flowers can be cooked and used like cauliflower. The plant is reported to contain 0.7% rutin, though the source does not specify which part; the leaves are the most likely candidate.

Traditional Uses

The leaf stem is eaten cooked. It is often stewed in pies and jams. Immature flowers are cooked and used like cauliflower.

This uses section is brief — help expand it

Medicinal Uses

The roots of many members of this genus are used medicinally. While R. palmatum is the primary species used in China, this cultivated species is reported to be used in Korea. Its properties follow those of R. palmatum: Chinese rhubarb has a long and proven history of herbal use, with its main effect being a positive and balancing action on the whole digestive system. It is one of the most widely used herbs in Chinese medicine and is considered safe and gentle enough for children. The plant is also an ingredient in the North American formula called essiac, used as a popular treatment for cancer, though its effectiveness has never been reliably proven or disproven as controlled studies have not been carried out. The other herbs in that formula are Arctium lappa, Ulmus rubra, and Rumex acetosella. The root is anticholesterolemic, antiseptic, antispasmodic, antitumor, aperient, astringent, cholagogue, demulcent, diuretic, laxative, purgative, stomachic, and tonic. Roots contain anthraquinones, which produce a purgative effect, alongside tannins and bitters that have the opposite astringent effect. Small doses act as an astringent tonic to the digestive system; larger doses act as a mild laxative. The root is taken internally for chronic constipation, diarrhoea, liver and gall bladder complaints, haemorrhoids, menstrual problems, and skin eruptions caused by an accumulation of toxins. It is not prescribed for pregnant or lactating women, nor for patients with intestinal obstruction. Externally, the root is used in the treatment of burns. Roots are harvested in October from plants at least six years old and dried for later use. A homeopathic remedy prepared from the dried root is used especially for diarrhoea in teething children.

Known Hazards

The leaves contain high concentrations of oxalic acid. Oxalic acid can lock up certain minerals (especially calcium) in the body, leading to nutritional deficiency. Cooking the plant will reduce the concentration of oxalic acid. Another report says that the leaves have the same concentration of oxalic acid in the stems as they do in the leaves and it is not the oxalic acid that makes them poisonous. It says that any toxic properties of the leaves is more likely to be due to the presence of glycosides. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition.

Distribution

It is a temperate plant. It suits hardiness zones 1-9.

Where It Grows

Asia, Siberia, USA,

Cultivation

A very easily grown plant, tolerant of considerable neglect, it prefers a deep, fertile, moderately heavy, humus rich, moisture retentive, well-drained soil in sun or semi-shade. It succeeds in most soils provided the drainage is good and will grow in the dappled shade of trees so long as there is sufficient side light. It grows well in heavy clay soils. Tolerates acid conditions but prefers a pH in the range 6.5 to 7. Plants are very cold hardy, tolerating temperatures down to at least -20°c. The plant does not like hot summers, however, and is likely to die in warmer climates. Rhubarb is a long-lived and almost indestructible perennial plant. It is often cultivated for its edible leaf stems, there are many named varieties. Most cultivars produce edible stems from spring to early summer, though 'Glaskin's Perpetual' can be harvested throughout the summer. By digging up the roots in the autumn and exposing them to frost, earlier growth will be initiated. These roots can then be transferred to a cold frame or other protected area where they will produce their edible stems in late winter. It is also possible to produce earlier crops outdoors by covering the plants with a layer of straw and an upturned bucket. This species is probably of hybrid origin, R. rhaponticum x R. palmatum. It hybridizes freely with other members of the genus. Plants in this genus seem to be immune to the predations of rabbits.

Propagation

Seed is best sown in autumn in a shaded cold frame, though spring sowing in a cold frame is also possible. As this species is a hybrid, it will not necessarily breed true from seed, though this does provide an opportunity to select superior plants from among the seedlings. Once large enough to handle, prick seedlings out into individual pots and grow them on in a greenhouse or cold frame through their first winter, then plant out in spring. For division, work in early spring or autumn, splitting the rootstock with a sharp spade or knife and ensuring at least one growth bud per division. Larger divisions can go directly into their permanent positions; smaller ones are better potted up and grown on in light shade in a cold frame until well established before planting out in late spring or early summer.