Maca has one of the highest frost tolerances among other native cultivated plants, since it is able to grow in the puna where only alpine grasses and bitter potatoes thrive (Bonnier 1986). The natural habitat of highland Peru where maca is grown has an average minimum temperature of -1.5°C and an average maximum of 12°C (Tello et al. 1992). Frost is frequent and temperatures can get as low as -10°c. The relative humidity is high, with an average of 70%. The natural soil in the maca \ production area is acidic, having a pH of 5 or less (Tello et al. 1992).
Although production of maca is restricted primarily to the central Andes of Peru, it can be grown successfully in other parts of the world. Field experiments in Davis, California indicate that this crop can be grown during the winter in this area a as an annual crop if irrigation is available throughout its whole life cycle. At Davis, 4 to 6-week-old seedlings transplanted in the field at the middle of September initiated hypocotyl development in 6-8 weeks. At this time of the year day length is approximately 10 hours and mean soil temperature approximately 12°c. The 'hypocotyls' reached a maximum size of 35-50 mm in diameter 7 months after transplanting, when day length was over 13 hours and mean soil temperature was approximately 20°c. By the middle of March, at the end of the rainy season, irrigation water was supplied as needed. Floral stems developed at this stage at the base of the stem, reaching anthesis and fruit-setting 8-9 months after sowing the seed. Therefore, most of the plants completed their seed-to-seed cycle in 10-11 months.
Experiments on photo period response in growth chambers demonstrate that maca does not require short days for general development, hypocotyl enlargement or flowering. Hypocotyl enlargement takes place at similar rates under either short (12 hours) or long days (14 hours). Similarly, flowering takes place independently of day length and without need of a vernalization period (Quirós et al. 1996). It is unknown, however, whether vernalization will promote more profuse and coordinated flowering in this species. From the results of these experiments, maca can be considered photoperiod-neutral and can be grown as an annual or biennial species, depending of water availability and optimal temperatures. Low temperatures and water availability during the growing season seem to be more important than day length in the development of the maca plant. Therefore, with adequate water supply to the plants and cool temperatures, in situ as well as ex situ germplasm conservation activities can be carried out for maca without much impediment.