Although amaranth is classified as a vegetable, in the kitchen the seeds are cooked and used like a grain. You can also use the highly nutritious, broad leaves of the amaranth plant as a substitute for spinach or kale. Amaranth is native to South America and the plant was highly regarded in Aztec and Inca cultures. North American gardeners may be familiar with a wild variety of amaranth known as red-rooted pigweed (Amaranthus retroflexus). The seeds and leaves of pigweed are also edible, although they are of a somewhat lower quality than cultivated amaranth. Flower gardeners know ornamental amaranth under the name "love lies bleeding."
Prepare the site by removing any sod or weeds. Amend the soil with compost if necessary. Amaranth does best in very fertile soil. Amaranth prefers loose, well-drained soil, but will also tolerate some heavier clay.
Plant amaranth when the danger of frost has passed. Amaranth likes hot weather and germinates best when the soil is between 18.3 and 23.9 degrees Celsius.
Sow amaranth seeds shallowly so that they are only covered with about one quarter inch of soil. Plant two or three seeds every six inches, then later thin them to one plant every six inches. The rows should be about 30 inches apart. For larger plantings, one to two pounds of amaranth seeds will cover an acre of land.
Water amaranth sparingly. The plant is very drought tolerant and only requires 10 inches of water throughout the growing season.
Apply a thin layer of mulch between the rows of amaranth to keep weeds down.
Harvest the leaves as the amaranth plant is growing. As long as you never pick more than one quarter of the leaves from any single plant, you should still be able to harvest the seeds later. Young greens may be eaten raw, and older leaves can be cooked like spinach.
Harvest the seeds when they fall easily from the seed head, about three months after germination. Bend the stalks over a bucket and brush the seeds off with your fingers.
Winnow the seeds by pouring them back and forth between two buckets while standing in front of an electric fan. This will blow away any chaff or other non-seed residue. You may also use a fine screen to clean amaranth seeds.
Allow the seeds to dry on trays in the sun or indoors near a stove or furnace for several days, until the seed is completely dry.
Store amaranth in an airtight container such as canning jars or plastic buckets with tight fitting lids. Amaranth should be stored away from heat or direct sun and should be used within one year of harvest.
Cultivated amaranth will hybridise with wild pigweed or ornamental amaranth. Keep your garden well-weeded if you plan to save your own amaranth seeds, and plant ornamental and culinary amaranth as far away from each other as possible.