Siberian Rhubarb

Family

Polygonaceae

Habit

perennial

Height

1.2 m

Spread

1.2 m

Growth

medium

Lifespan

15 years

First yield

after 2 years

Hardiness

zone 3–8

Shade tolerance

light shade

Soil

Sand, Silt

Soil moisture

semi-dry – very moist

pH

5.5 – 7.5

Synonyms

Garden rhubarb, Garden Rhubarb

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

Edible: The leaf stalks of Siberian rhubarb are used like those of the garden cultivars, but come thinner, more fibrous and more acidic, which is why the species could never compete with the bred forms in the kitchen. It is harvested from April to June and made into compote, cake and juice. The young, still-closed flower shoots can be peeled and steamed like asparagus, a spring practice common in Mongolia and Siberia. For centuries it was not the vegetable but the root that mattered economically: as a dried drug it travelled the Silk Road to Europe and was at times among the most expensive trade goods of all. The leaves are unsuitable for eating because of their oxalic acid content.

Other uses: For centuries the root of Siberian rhubarb was among the most valuable trade goods between Asia and Europe. Dried and cut into pieces it travelled the Silk Road and in medieval Europe was weighed against spices and precious metals; in the 18th century the Russian crown even ran a state rhubarb monopoly with its own quality control at Kyakhta on the Mongolian border. The anthraquinones it contains also dye: the root colours wool and silk in warm yellows and golds, and with different mordants into orange-browns. As with garden rhubarb, the large leaves serve as a metal scouring agent and as a broad mulch.

Site: Siberian rhubarb is a substantial, long-lived perennial that occupies around a square metre and stays in the same place for decades, so it belongs at the edge of the bed rather than in the rotation. It is distinctly hardier and more drought-tolerant than the garden cultivars and copes with leaner, stonier ground, but it wants full sun to light half-shade and free-draining soil without waterlogging. A cold winter is a requirement, not a risk. As a wild species it bolts far more readily than the bred forms and seeds itself freely if the flower stem is left standing. The oxalic-acid-rich leaves are unsuitable for small livestock and poultry. Care: Cover with compost or rotted manure in autumn, which is feeding enough; its nutrient demand is lower than that of the garden cultivars. Water in spring dry spells. Break out flower shoots consistently as soon as they appear, or the plant's strength goes into seed and the clump sows half the bed; if you want seed, leave a single stem deliberately. Harvest from the second season by twisting out, never by cutting, and only until the end of June. Divide the clump every four to six years or the centre ages out. Disease is rare and the species counts as more robust than the cultivars; mosaic viruses and root eelworm appear occasionally.

Unlike garden rhubarb, Siberian rhubarb is a true species and can therefore be raised from seed. Collect the seed in late summer once the winged nutlets have turned brown and sow outdoors in autumn; it is a cold germinator and comes up after winter. For spring sowing, four weeks of cold stratification in moist sand helps. Seedlings vary among themselves, which is normal for a wild species and allows the strongest individuals to be selected; two to three years pass before the first harvest. Division of the rootstock in late autumn or early spring is faster and truer to form: each division needs at least one strong bud and a decent piece of rhizome, the cut surfaces should dry for a day, and the bud is planted just below the surface.

As a wild species Siberian rhubarb bolts more readily than the bred cultivars and therefore flowers more often in the garden, which makes it ecologically more valuable. The cream-white panicle, up to two metres tall and many-flowered, appears in May and June and is heavily worked by honeybees, hoverflies, beetles and short-tongued wild bees; the individual flowers are small and open, so the nectar lies exposed and is reachable even for short-tongued species. As an Asian neophyte it has no specialised native species tied to it. The large, oxalic-acid-rich leaves are avoided by slugs and deer and form a cool, moist canopy through the summer under which ground beetles, spiders and amphibians find cover. Finches take the ripe nutlets.

Notable: parent species of garden rhubarb, diploid (2n=22) against the tetraploid cultivars; its dried root was one of the most expensive trade goods of the Middle Ages via the Silk Road; 18th-century Russia ran a state rhubarb monopoly with quality control at Kyakhta; bolts more readily than garden cultivars → flowers more often + self-seeds.

Central Asia: southern Siberia, northern Mongolia, northern and central China. Siberian rhubarb is the wild species behind garden rhubarb and is centred on the Dauria region around and east of Lake Baikal and in northern Mongolia. From there its range extends south into the mountains of northern China. It reached Europe first as dried root in the medicine trade, imported through Arab intermediaries from the 11th century; as a living plant it arrived in the 18th century and, together with Balkan Rheum rhaponticum, formed the basis of vegetable breeding. In central Europe it is kept in gardens and botanical collections and does not naturalise.

In its native range Siberian rhubarb grows on stony slopes, river gravels, mountain steppe and woodland edges in the continental ranges of southern Siberia and Mongolia, generally between about 1000 and 3000 metres. These sites are open, sunny and free-draining, and by no means permanently moist in summer; a strong, deep storage root bridges dry spells, and the long, very cold winters with reliable snow cover are part of the species' rhythm. It is therefore considerably hardier and more drought-tolerant than the garden cultivars and less demanding of nutrients, though it yields thinner stalks in return.