CULTURAL DIRECTIONS 439 



colored flesh. This sort is extensively grown for the 

 earliest market, but it is of only fair quality. It yields 

 well if allowed to remain until late in the season. 



BLACK SPANISH, or ''NIGGER CHOKER." The Black 

 Spanish vines are very long, vigorous, and dark purple 

 in color. The potatoes are long, cylindrical, crooked, or 

 bent ; dark purple in color, with snowy white flesh and poor 

 quality. This variety is grown mostly for stock feeding. 



SHANGHAI. The vines of the Shanghai variety are 

 large and vigorous ; the potatoes long, cylindrical ; the 

 outside color almost white. The flesh is creamy white, 

 becoming darker in cooking. When baked the flesh is 

 somewhat dry and mealy and the flavor rather poor. This 

 variety yields fairly well and is adapted for use as stock 

 food in the Gulf Coast States. 



627. Climatic requirements. There are extensive 

 areas in the United States which are well adapted to 

 sweet potatoes, mainly because of suitable climatic con- 

 ditions. The plant is very tender and demands high tem- 

 peratures. An abundance of sunshine is essential to 

 high yields. Although a liberal rainfall is desirable dur- 

 ing the growing season, it is detrimental when the tubers 

 are maturing, because it encourages excessive vine 

 growth at the sacrifice of tubers. There should be a 

 growing season of not less than 4^2 months without 

 frost. Warm nights are important to obtain the best 

 results. This vegetable is often grown in northern gar- 

 dens, but it is futile to attempt its cultivation commer- 

 cially where climatic conditions are unsuitable. 



628. Soils. The lighter soils are invariably regarded 

 as the best for sweet potatoes. A moderate proportion 

 of sand in the top soil, with a fairly retentive subsoil, 

 provides ideal conditions. Whatever the soil type, it 

 must be warm, loose and well drained. Stiff, heavy soils 

 should never be planted with this vegetable. When it is 

 necessary to use such soils in supplying sweet potatoes 



