Method - sweet potatoes are normally planted on ridges or mounds, the former being preferred although experiments in Zaire suggest that mounds are better, as they encourage tuber formation. In the tropics, small farmers sometimes interplant sweet potatoes with beans or cassava. Once planted in the field sweet potatoes normally receive little attention apart from weed control at the early stages of growth and the maintenance of ridge height and shape. In the USA, extensive use is now made of a wide range of effective herbicides for the control of weeds, including naptalam, allidochlor, chloramben, vernolate, diphenamid, prometryn; normally application is pre-planting or pre-emergence.
Field spacing - the spacing used is determined by the following factors: growth habit and root-setting characteristics of the cultivar; type and fertility level of the soil; length of the growing season; and the purpose for which the crop is required. In the last case, if the tubers are required for the fresh market, then high yields of tubers of uniform shape and size are of primary importance, while for canning or freezing small tubers with a diameter of 2.5-5 cm and a length of 7.5-15 cm are required; for industrial uses, such as the manufacture of starch and dehydrated flakes, large roots are preferred because they are easier to handle and losses during preparation are less.
In the USA, sweet potatoes are commonly planted 30-37.5 cm apart in rows which are 90-105 cm apart in well-drained light soils and 120 cm apart in heavier soils. In the tropics, the vine cuttings are usually spaced 22.5-30 cm apart in ridges 60-75 cm apart.