Chinese Yam (Dioscorea batatas)
At a glance
- Lifecycle
- Perennial (hardy)
- Exposure
- Full sun
- Frost limit
- −28.9 °C
Cultivation
An easily grown plant, succeeding in a fertile well-drained soil in a sunny position or light shade. Plants are hardy to at least -18°c. This species of yam is much cultivated in China for its edible root which can be up to 1 metre long. The yam is a climbing plant that supports itself by twining around the branches of other plants. It can be grown successfully into small bushes or, perhaps simpler when being grown as a root crop, it can be grown up a frame in a similar manner to growing runner beans[K]. Plants produce tubercles (small tubers that are formed in the leaf axils of the stems), and can be propagated by this means[K]. The small white flowers have a pleasant scent of cinnamon. There is some confusion over the correct name for this species. One report says that D. batatas is an invalid name that is often erroneously applied to two distinct species D. opposita and D. japonica. Dioecious. Male and female plants must be grown if seed is required.
Propagation
Seed - sow March to April in a sunny position in a warm greenhouse and only just cover. It germinates in 1 - 3 weeks at 20°c. Prick out the seedlings as soon as they are large enough to handle and grow on in a greenhouse for their first year. Plant out in late spring as the plant comes into new growth. Basal stem cuttings in the summer. Division in the dormant season, never when in growth. The plant will often produce a number of shoots, the top 5 - 10 cm of the root below each shoot can be potted up to form a new plant whilst the lower part of the root can be eaten[K]. Tubercles (baby tubers) are formed in the leaf axils. These are harvested in late summer and early autumn when about the size of a pea and coming away easily from the plant. They should be potted up immediately in individual pots in an unheated greenhouse or cold frame, covering them with about 10mm of soil. Protect them from mice etc and keep the soil moist but not wet. They should come into growth in the spring, plant them out in early summer when in active growth[K].
Edible uses
Tuber - cooked. Fruit. A starchy flavour, it is said to be very good for the health. We wonder if this report is referring to the tubercles[K].
Medicinal uses
The Chinese yam, called Shan Yao in Chinese herbalism, is a sweet soothing herb that stimulates the stomach and spleen and has a tonic effect on the lungs and kidneys. The tuber is anthelmintic, digestive and gently tonic. The leaf juice is used to treat snakebites and scorpion stings. The roots of most, if not all, members of this genus, contains diosgenin.
Habitat
Found in an apparently wild situation in valleys and on the slopes of hills in China.
Native range
Temperate E. Asia, though the exact range is not known.
Scientific synonyms Dioscorea polystachya