Culture
Pot or tub culture is recommended. All species are easy to grow from seeds, bulbils (small tubers produced at leaf axils), 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 a main food crop 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 (Ipomoea batatas) 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 and smooth skin, sweet, medium to high in beta-caretene
True yam: Rough and scaly skin, 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 or are grown as ornamentals. Some have escaped cultivation to become quite invasive in certain areas. Check local laws before adding these plants to your garden. Species you may find 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 polystachya (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, 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 small 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. This plant was introduced to the United States as a potential food crop but quickly escaped cultivation. It is considered highly invasive in Florida and other parts of the Southeast were it smothers native flora. It has also been reported as escaping cultivation in parts of the Midwest.
Dioscorea villosa (wild yam, colic-root): This native American yam is not edible, but contains several 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
Yams are generally quite problem free. Some species may be invasive in your area. Check local laws before adding these plants to your garden.
Uses
Large containers, vegetable gardens.