Yams vs. Sweet Potatoes
A major difference between yams and sweet potatoes is that yams are monocots and sweet potatoes are dicots. Additionally, yams are related to lilies and a member of the Dioscoreaceae family while sweet potatoes are a member of the morning glory family (Convolvulaceae). Yams are a root crop common to Africa and Asia while sweet potatoes are native to tropical Central and South America and the Caribbean. Until recently, the names were used interchangeably in grocery stores, but today the USDA has attempted to regulate the use of “yam” and “sweet potato.” Currently the use of “yam” to describe a sweet potato must be clarified with the addition of the term “sweet potato.”
Yam Plant Info
Now that we have all that straightened out, what really is a yam? There is probably as much yam plant info as there are species: 600 different species with as many uses. Many yams grow to giant sizes of up to 7 feet (2 m.) long and 150 pounds (68 kg.). Yams contain more sugar than sweet potatoes but they also contain a toxin called oxalate that must be thoroughly cooked before safe for ingestion. True yams need up to a year of frost-free climate before harvest whereas sweet potatoes are ready in 100-150 days. Yams are referred to by many other names including true yams, greater yam, and tropical yam. There are a number of varieties available for cultivation both for ornamental use and for harvest, such as Chinese yam plants, white yams, Lisbon yams, pei tsao, bak chiu, and agua yams. Yam plants are climbing perennial vines with heart-shaped leaves that are sometimes variegated and quite striking. Underground tubers develop, but sometimes aerial tubers develop as well in the axils of the leaves.
How Do You Grow Yams?
Growing Chinese yams or any of the other true yams requires tropical to subtropical temperatures. Several species exist here, mostly in Florida and other temperate regions as wild plants. When planting yams, whole small tubers or portions of larger tubers are used for seed pieces weighing 4-5 ounces (113-142 grams). Yams should be planted in temperate zones in March-April and harvest will take place 10-11 months later. Make 42-inch (107 cm.) rows with plants spaced 18 inches (46 cm.) apart and 2-3 inches (5-7.6 cm.) deep. Hill plantings spaced 3 feet (.9 m.) apart can also be used when planting yams. Support the vines with a trellis or similar support for the best results.
