<Li> IU = International units </Li> <Tr> <Td_colspan="2"> Percentages are roughly approximated using US recommendations for adults . Source: USDA Nutrient Database </Td> </Tr> <P> The plant does not tolerate frost . It grows best at an average temperature of 24 ° C (75 ° F), abundant sunshine and warm nights . Annual rainfalls of 750--1,000 mm (30--39 in) are considered most suitable, with a minimum of 500 mm (20 in) in the growing season . The crop is sensitive to drought at the tuber initiation stage 50--60 days after planting, and it is not tolerant to water - logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor . </P> <P> Depending on the cultivar and conditions, tuberous roots mature in two to nine months . With care, early - maturing cultivars can be grown as an annual summer crop in temperate areas, such as the northern United States and China . Sweet potatoes rarely flower when the daylight is longer than 11 hours, as is normal outside of the tropics . They are mostly propagated by stem or root cuttings or by adventitious shoots called "slips" that grow out from the tuberous roots during storage . True seeds are used for breeding only . </P>

Where are sweet potatoes grown in the us