People often confuse the yam and sweet potato. Although both are tubers, they belong to different botanical families -- the yam belonging to the lily family and the sweet potato belonging to the morning glory. Africa, the native land of the yam, grows 95 percent of more than 600 varieties of the crop. Yams favor tropical and sub-tropical weather during their growing season and do not tolerate freezing.
Tuber Cuttings
After harvesting, yams have a resting period for about three to four months throughout the dry season before they make suitable seeds. Disease-free plants produce suitable cuttings for growing yams and need planting before they sprout, usually in August. Gardeners cut tubers crosswise into three pieces. The cuttings lie out for one week to callous over after being washed with Bordeaux mixture, a solution of copper sulfate and lime in water, to protect them from diseases such as tuber rot.
Soil Preparation
Yams favor loose clay soil with good drainage. Gardeners test soils and adjust pH levels to about 5.5. They plow the planting area and dig trench rows with 3 1/2 feet between them. Gardeners then add compost into the trenches and check the soil for proper drainage. Tuber crops do not grow well in overly wet soils and require loose soil to allow room for drainage and growth.
Planting
After the tuber cuttings have lain out for one week, gardeners plant them 2 inches deep into the trenches with 18 inches between each planting. Gardeners lay mulch along the trenches after initial planting. Mulch keeps the ground moist without drowning the crop, protecting the tubers from extreme heat. About one month after twines emerge, gardeners place stakes into each mound at an angle to meet the stake in the adjacent mound, creating an A-frame structure for the two twines to climb and meet. The vines of yam plants are not sturdy and need support to produce high yields.
Maintenance
Plowing helps to bring up old plant debris and weeds for removal. After planting, gardeners must keep the planting area free of these organic materials throughout the growing season to prevent pest and fungal infestations. They weed the garden by hand and sometimes use pre-emergent sprays that kill weeds before they break ground. Gardeners fertilize the crop one month after twines emerge from the mounds and again about seven to nine weeks later. Gardeners prevent overly wet soils by evenly watering the crops.