The plant's growth is highly variable due to the number of different subspecies, varieties and landraces (domesticated plants or animals adapted to the environment in which they originated). However, it is generally undemanding and altitude-hardy; it is grown from coastal regions to over 4,000 m (13,000 ft) in the Andes near the equator, with most of the cultivars being grown between 2,500 m (8,200 ft) and 4,000 m (13,000 ft). Depending on the variety, optimal growing conditions are in cool climates with temperatures that vary between −4 °C (25 °F) during the night to near 35 °C (95 °F) during the day. Some cultivars can withstand lower temperatures without damage. Light frosts normally do not affect the plants at any stage of development, except during flowering. Midsummer frosts during flowering, a frequent occurrence in the Andes, lead to sterilization of the pollen. Rainfall requirements are highly variable between the different cultivars, ranging from 300 to 1,000 mm (12 to 39 in) during the growing season. Growth is optimal with well-distributed rainfall during early growth and no rain during seed maturation and harvesting.
Quinoa has been cultivated in the United States, primarily in the high elevation San Luis Valley of Colorado where it was introduced in 1983. In this high-altitude desert valley, maximum summer temperatures rarely exceed 30 °C (86 °F) and night temperatures are about 7 °C (45 °F). Due to the short growing season, North American cultivation requires short-maturity varieties, typically of Bolivian origin.
Several countries within Europe, including France, England, The Netherlands, Belgium, Germany and Spain, have successfully grown quinoa on a commercial scale. As of 2015, within the UK, crops have been grown to scale and mechanically harvested in September.
Quinoa plants do best in sandy, well-drained soils with a low nutrient content, moderate salinity, and a soil pH of 6 to 8.5. The seedbed must be well prepared and drained to avoid waterlogging.
Soil and pests
Yields are maximised when 170 to 200 kg (370 to 440 lb) N per hectare are available. The addition of phosphorus does not improve yield. In eastern North America, it is susceptible to a leaf miner that may reduce crop success. (It also affects the common weed and close relative Chenopodium album, but C. album is much more resistant.)
The genome of quinoa was sequenced in 2017 by researchers at King Abdullah University of Science and Technology in Saudi Arabia. Through genetic engineering, the plant is being modified to have higher crop yield, improved tolerance to heat and biotic stress, and greater sweetness through saponin inhibition.
Harvested quinoa seeds
Traditionally, quinoa grain is harvested by hand, and only rarely by machine, because the extreme variability of the maturity period of most Quinoa cultivars complicates mechanization. Harvest needs to be precisely timed to avoid high seed losses from shattering, and different panicles on the same plant mature at different times. The crop yield in the Andean region (often around 3 t/ha up to 5 t/ha) is comparable to wheat yields. In the United States, varieties have been selected for uniformity of maturity and are mechanically harvested using conventional small grain combines.
Threshing quinoa in Peru
The plants are allowed to stand until the stalks and seeds have dried out and the grain has reached a moisture content below 10%.
Handling involves threshing the seedheads from the chaff and winnowing the seed to remove the husk. Before storage, the seeds need to be dried in order to avoid germination. Dry seeds can be stored raw until being washed or mechanically processed to remove the pericarp to eliminate the bitter layer containing saponins. The seeds must be dried again before being stored and sold in stores.