Dioscorea batatus is called chinese yam, cinnamon vine, wild yam or chinese potato. It is native to the mountainous regions of Japan and China, where it was discovered by Decne in 1854.
It has spread out throughout the world as cultivated plant. It's a robust twining perennial and its shoots die down to the ground every winter. It attains the height of 6 m in its native habitat and about 3,5 m in Poland. Its shoots twine clockwise round the supports (unlike to Dioscorea sativa, sweet potato widely cultivated in tropical countries). Flowers are small, white-green-yellow with a pleasant cinnamon scent and appear in June - August. Attractive leaves are dark green, lustrous, cordate, 7 to 9-veined and slightly lobed. The cultivar 'Variegata' has green leaves mottled with white and, when young, the shoots, leaf petioles and leaf veining are crimson. Lower parts of the stems are often bare, both in the species and in its cultivar. In late summer and autumn small brown aerial bulbils, the size of a pea or a hazelnut, appear in leaf axils. They can be used either for propagation or eaten - they are tasty and have a nutty flavour.
| Dioscorea batatus - leaves - photo Sz. Marczynski |
Requirements
Chinese yam requires a sunny site with fertile, moist, well drained humus soil. It tolerates frosts up to -20oC and if you sprinkle the soil round the plant with bark or wooden chips, it will sustain even much harsher winters.
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Dioscorea batatus - a bulbil - photo Sz. Marczynski |
Tubers should be dug out at the end of the second year of cultivation, when the plant has already spread and the bulbs are big enough. They can be kept in a cool place (but sheltered from frost) even for several months. During this time they should be protected from drying.
Dioscorea batatus can be propagated from seed (you need to have both female and male specimens), aerial bulbils (gathered in autumn after ripening, but before they fall) or from the upper parts cut from the ground tubers (with dormant buds). In spring they can be planted into pots indoors and, once the danger of ground frosts is over, directly into the ground. The simplest way, however, is to buy a plant in a container from a garden centre or a nursery.
Dioscorea batatus 'Variegata' - leaves - photo Sz. Marczynski | Dioscorea batatus - leaves, flowers and aerial bulbils - photo Sz. Marczynski |