Most healthy plants produce between one and three tubers.
Although people sometimes use the terms "yam" and "sweet potato" to refer to the same vegetable, they are actually two different species. A true yam grows only in the tropics, whereas sweet potatoes grow in tropical and subtropical climates, according to the University of Illinois Extension. Yams also grow differently than sweet potatoes, despite their similar appearance. Yams are generally more difficult to cultivate in the U.S. due to the strict growing conditions required.
About
Yams are a type of tuber that grows on vines in the ground. They have a coarse, scaly outer skin and an orange-pink dense flesh. Yams can grow large, up to 7 feet in length, and weight as much as 150 lbs., notes the U.S. Department of Agriculture. They typically have a starchy taste and tend to have a drier texture than other tubers, like red bliss potatoes.
Planting
Small tubers can be planted as seeds. Commercial and home gardeners often select tubers for planting with two or three visible eyes -- raised nodules on the outer skin that eventually become roots -- since these tubers sprout quicker. Yams are typically planted in the dry month of August just before rainy season. The tuber requires seven to 12 months to fully develop, at which point the plant's leaves and stems begin to shrivel and die. Yams are harvested by digging around the plant and carefully lifting it from the soil to reveal and trim vines bearing yams. Once harvested, yams require a few days in the sun to fully dry before they can be stored and shipped to prevent injury.
Climate
Yams need plenty of moisture and sun with consistent temperatures of about 77 to 86 degrees Fahrenheit over almost an entire year's time to fully mature. When temperatures are at or below 68 degrees Fahrenheit, it restricts growth. A brief temperature drop below freezing can kill yam vines. Mulch is often used to protect plants from extreme temperatures while yams develop.
Soil Conditions
Yams must be grown in nutrient-rich, loose soil that provides the flexibility that yams need to freely grow and expand. Soil with ample drainage is preferred, which is why the ideal location for planting yams is often on banks and hillsides. Yams are frequently planted in trenched columns that make it easier for machines to plow and harvest crops.
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