white, with a clear distinction between skin and interior. They lack noticeable fibrous material.
Horticultural Varieties. There is enormous variation in this crop: a single market may display six distinct types, and a market nearby may have six entirely different ones. Based on tuber appearance, some 50–70 distinct clones exist.14 Some have been transported throughout the length of the Andes.
Daylength. Daylengths of 10–13.5 hours are needed for tuber production in the varieties most commonly grown in the central Andes. However, some ulluco is grown in northern Argentina at 27°S latitude, and it seems likely that daylength-neutral types can be found in such places.15
Rainfall. Moisture requirements are unknown, but probably are in the range of 800–1,400 mm during the growing season in the Andes.
Altitude. Ulluco is an important mid- to high-altitude crop from Venezuela to Chile.16 However, it has also been grown at sea level in Canada, England, and Finland.
Low Temperature. The plant grows well in cool, moist conditions and is frost resistant.
High Temperature. Although they thrive under high light intensities, ulluco plants produce tubers poorly in hot climates.
Soil Type. This crop tolerates a wide range of soil conditions. Not unexpectedly, however, it does best in a fertile, well-drained loam with a pH between 5.5 and 6.5.