The ornamental yam, a captivating plant often sought for its aesthetic qualities, belongs to the large Dioscorea genus, which also contains the true edible yams. These showy varieties are cultivated exclusively for their striking foliage and unique growth habit rather than for any culinary purpose. Plants like Dioscorea discolor have become popular in gardening due to their dramatic, fast-growing vines, making them an excellent choice for adding tropical flair to a space. It is important to recognize this plant as a decorative specimen, setting it apart from its starchy tuber-producing relatives.
Distinctive Features of Ornamental Yam
The primary appeal of ornamental yams lies in their highly decorative foliage, which features a remarkable array of colors and textures. Many species, particularly Dioscorea discolor, exhibit large, velvety, heart-shaped leaves often patterned with dramatic variegation. This patterning can include shimmering veins in silvery-white, pink, and deep green, often contrasted by a reddish-purple underside. The leaves are situated on slender, twining stems that grow rapidly, sometimes reaching up to 12 feet in a single growing season.
This vigorous, climbing growth necessitates a support structure, as the stems naturally twist counterclockwise around a trellis or moss pole. The visual contrast between the bold, colorful leaves and the architectural vining habit creates a lush, layered effect. Ornamental varieties are specifically selected and bred to maximize this vibrant leaf coloration.
Essential Growing Conditions
Ornamental yams thrive in conditions that closely mimic their native tropical and subtropical environments, primarily requiring warmth and bright, consistent light. To maintain the most vibrant leaf coloring, the plant should be situated in an area that receives bright, indirect light, though some varieties can tolerate a few hours of gentle morning sun. Excessive exposure to harsh, prolonged afternoon sun, however, can scorch the delicate foliage and cause the colors to fade.
The proper soil mixture is equally important, demanding a rich, well-draining composition, often achieved by amending a standard potting mix with extra organic matter. During the active growing period, which typically spans spring through fall, the soil should be kept evenly moist, but never waterlogged. The plant performs best in temperatures ranging from 65 to 85 degrees Fahrenheit and must be protected from any temperatures falling below 60 degrees Fahrenheit.
Safety and Edibility Concerns
A fundamental distinction must be made between these ornamental plants and the culinary yams sold for consumption, as the decorative varieties are unsuitable for eating. The tubers of many ornamental Dioscorea species contain various toxic compounds that can be harmful if ingested. These compounds often include steroidal saponins and the toxic alkaloid dioscorine.
Other species, such as Dioscorea bulbifera, contain furanoditerpenoids like diosbulbin B, which are linked to severe toxicity, including liver damage. For this reason, the tubers of ornamental yams should not be consumed by humans or pets, and gardeners should exercise caution if children or animals are present. The development of severe vomiting, diarrhea, or neurological symptoms following ingestion requires immediate medical attention.
Propagation and Dormancy Management
Cultivation of ornamental yams involves careful management of their natural life cycle, particularly the dormant period. These perennial plants grow from an underground tuber, and in non-tropical climates, the leafy vines will naturally begin to die back as temperatures cool in the late fall. At this point, the water supply should be drastically reduced to allow the plant to prepare for its winter rest.
In areas prone to frost, the dormant tuber must be lifted from the ground or container and stored indoors for the winter. The tuber should be cleaned and kept in a cool, dark, and non-freezing location, such as a basement or garage, until the following spring.
Propagation can be achieved by dividing the main tuber before replanting or by taking stem cuttings from the actively growing vine during the summer months. Replanting the tuber in fresh soil once temperatures consistently remain above 60 degrees Fahrenheit will encourage the resumption of the growth cycle.