Growing tropical yams in Kentucky can be difficult. True yams originate in warm climates and require seven to 10 months to mature. During that entire period, the temperature needs to remain above 57 F in order for the plant to grow at all, with temperatures above 70 F being optimal to prevent serious growth retardation. In Kentucky the average temperature does not stay above 57 F for more than five to six months, according to weather data for the state. If you intend to grow tropical yams in Kentucky, you will need to grow them in a heated greenhouse to maintain the proper growing temperature.
Till the soil in the greenhouse to a depth 6 inches using the shovel. Yams can grow in a wide variety of soil types, but prefer high fertility. If your soil is low in fertility, you will need to introduce an amendment of organic material (such as manure) to the soil at this time. Till it into the soil.
Place the seed tubers or tuber pieces one inch deep into the soil and cover. Space them 12 to 15 inches from each other. If you are planting in rows, keep each row 3 feet from the next.
Water the ground thoroughly. Tropical yams are adapted to tropical conditions, and hence need substantial amounts of water. In their native habitat they are grown during the rainy season, which can provide substantial amounts of rain daily depending on the area.
Keep the greenhouse temperature above 70 F. This is important for germination and growth, and will need to be maintained for the entire growing season of seven to 10 months. The plant will not develop properly at lower temperatures.
Water the plants daily and generously in order to imitate tropical rainy season weather.
Stake the plants soon after they have begun to grow. Yams are vines and will produce higher yields if staked.
Harvest the yams after seven to 10 months. The tubers will remain dormant for two to four months after reaching maturity, so an immediate harvest is not necessary, according to online resource Infonet-Biodivision. The yams should be harvested carefully with hand tools such as a shovel or trowel to avoid damaging the tubers.