Dioscorea (vegetable group)
Common Name: white yam
Type: Bulb
Family: Dioscoreaceae
Zone: 9 to 12
Height: 1.00 to 2.00 feet
Spread: 4.00 to 20.00 feet
Bloom Time: Seasonal bloomer
Bloom Description: White
Sun: Full sun to part shade
Water: Medium
Maintenance: Low
Suggested Use: Vegetable

Culture

Pot or tub culture is recommended. All species are easy to grow from seeds, bulbils (little tubers), tubers, or cuttings. Plant in fertile, well-drained soil, in full sun or partial shade. Dioscorea species can grow rapidly once established, up to 6 inches per day, so are heavy feeders. The underground tubers can grow very large over time; adequate size pots should be provided. Support for the vine will be necessary. Provide ample moisture during active growing season. Some are hardy in this area, others must overwinter inside.

Noteworthy Characteristics

Yams are the staff of life for millions in the tropical regions of the world. True yams are the third most important tropical root crop after cassava and sweet potatoes. The name ‘yam’ properly belongs to the various species of Dioscorea. However, Americans call their sweet potatoes yams. Today, even supermarkets and canners often label orange sweet potatoes as yams. The true yam is very different in botanical terms, appearance, taste, texture, and color. A quick comparison of the two is as follows:

Characteristics:
Sweet potato: Thin smooth skin, blocky, sweet, medium to high in beta-caretene True yam: Rough and scaly skin, long cylindrical, starchy, very low in beta-caretene

True yams include hundreds of mostly tropical, fast growing, climbing or crawling vines with attractive heart-shaped leaves, usually with large or even gigantic roots that is some species continue to grow and increase in size for years. Many are edible, some contain rather exotic compounds, and some are invasive pests that make kudzu look tame. Species you may find available include the following:

Dioscorea alata (white yam, water yam): Probably the most cultivated, edible, true yam. Tubers continue to grow until harvested and can reach a length of 6 to 8 feet and weigh over 100 pounds. These are not hardy in this area.

Dioscorea batata (cinnamon vine, Chinese yam): This white fleshed edible tuber of good flavor has a hardiness rating of Zones 5 to 10, and will remain alive in the ground overwinter as far north as New York, sending up handsome tall twining shoots in the Spring. It now ranges from Vermont south to Georgia and west to Oklahoma and Texas. The vine vegetatively reproduces by bearing little tubers (bulbils) in the leaf axils that can be planted immediately. Bulbils float in water and can be dispersed in floods. Bulbils as little as 3/8 inch in diameter can produce new vines. In the Great Smoky National Park, it has become a serious threat to native plants and has the potential to become a major pest plant in the United States.

Dioscorea bulbifera (Air Potato): This true yam also produces axillary tubers but these can sometimes weigh several pounds. These are edible and potato like in flavor. The root tubers are usually absent or insignificant.

Dioscorea sp. (air potato, bitter yam, giant yam vine, Hawaiian bitter yam): Similar to both D. alata and D. bulbifera, there appears to be some uncertainty on the part of Florida botanists on the proper botanical name of the bitter yam, but total agreement that the highly attractive ornamental is aggressively colonizing much of Florida, and little seems to stop it. Once fully established, it smothers native flora. While Florida researchers could find no written references to this yam invading other continental States, they have received reports of it being found in Southern Illinois.

Dioscorea villosa (wild yam, colic-root): This native American yam is not edible, but is a virtual cornucopia of organic compounds of medical interests. It grows wild from Rhode Island to Florida and Texas and has the characteristic highly ornamental heart-shaped leaves and vining habit.

Genus name honors Pedanios Dioscorides, first century Greek physician and herbalist.

Problems

Dioscorea species are generally quite problem free.

Garden Uses

It is suggested that Dioscorea be limited to pot culture.