Soil Preference. Quinoa and amaranth are responsive to nitrogen and phosphorous. Plants grown in average garden soil will be four-feet to six-feet tall, while those grown in rich soil or compost may reach over eight feet. Optimum soil is a well-drained loam but both plants will do well in all but poorly aerated clay soils.
Quinoa Varieties. Named varieties of amaranth and quinoa are increasingly available from seed companies. Most North Americans would be hard-pressed to describe the subtle differences in flavour between cultivars. Black-seeded varieties of amaranth stay quite gritty when cooked, so it is best to use these varieties just for their leaves. All the golden and light-colored amaranths I’ve tried are excellent cooked as whole grains and all have delectable greens.
Planting Times For Quinoa. Quinoa grows best where maximum temperatures do not exceed 90°F (32°C) and nighttime temperatures are cool. For most southern Canadian and northern U.S. sites, the best time to plant quinoa is late April to late May. When soil temperatures are around 60°F (15°C) seedlings emerge within three to four days. However, when quinoa seeds are planted in soil with night-time temperatures much above that, quinoa, like spinach, may not germinate. In this instance, it’s best to refrigerate seeds before planting.
Amaranth is a warm season crop that requires full sun. Best germination occurs when soil temperatures range from 65 to 75°F (18-24°C). For southern Canada and the northern U.S., this usually means a late May or early June planting.
Sowing. The small seeds of amaranth and quinoa will germinate more successfully with a finely prepared surface and adequate moisture. Seeds should be sown no more than one-quarter inch deep in rows one and a half- to two-feet (45-60 cm) apart or wide enough to accommodate a rototiller between the rows without damaging the plants. Planting can be done by hand or with a row seeder. Plants should eventually be thinned 6 to 18 inches (15-45 cm) apart. (Thinnings make great additions to salad.)
One gram of seed will sow 50 feet (15 m) of row. An acre requires about one pound of seed.
Maintenance. Quinoa resembles lamb’s-quarters and amaranth resembles red-rooted pigweed, especially in the early stages of growth, so it is best to sow seed in rows to make weeding less confusing. Sowing amaranth cultivars with purple leaves also simplifies weeding. Since seed is small, you can avoid considerable thinning by mixing it with sand or radish seed before sowing, as is sometimes done with carrots. Amaranth and quinoa are low-maintenance crops but weeds, especially at the beginning, should be discouraged by cultivation or mulching.
Soil moisture is probably sufficient until early June to germinate the seed. Given good soil moisture, don’t water until the plants reach the two- or three-leaf stage. Quinoa and amaranth appear slow growing at first but both are extremely drought tolerant and do well on a total of 10 inches (25 cm) of water or less. As the plants reach about one foot in height, they start to grow very rapidly, the canopy closes in, weeds are shaded out and less moisture is lost through evaporation.
You may have noticed occasional lamb’s-quarter or amaranth weeds succumbing to munching by insect larvae in the flowerheads and the same is sometimes true of their cultivated cousins. This won’t have any serious impact on the harvest.
Harvesting. Quinoa is ready to harvest when the leaves have fallen, leaving just the dried seedheads. Seeds can be easily stripped upwards off the stalk with a gloved hand. Quinoa resists light frosts especially if the soil is dry. So long as maturing seed is past the green stage, frost will cause little damage and harvesting can be done a day or two later. Extreme hot weather and warm nights inhibit fruit set. It is important to watch the weather when quinoa is ready to be harvested: if rained on, the dry seed can germinate. If the heads are not completely dry, harvest them when you can barely indent the seeds with your thumbnail. They should then be thoroughly dried before storage.