Sow amaranth seeds indoors. Individual 3 inches pots are best. If planting in a shared bed, space seedlings 10 to 14 inches apart from one another. Lightly cover each seed with about 1⁄4 inch of soil, and place the bed out of direct sunlight, in an area where is will not be exposed to cold. Keep the seeds around 70 °F. Your seeds will germinate in 10 to 14 days.
Use well-draining soil with a pH between 6 and 7. The soil in which you grow your amaranth should not contain too much clay. Additionally, test your soil’s pH. Amaranth is less sensitive to soil variability than many other plants, but will grow best in soil with a pH between 6 and 7. Extremely rich soil will actually reduce a plant’s number of flowers.
Plant amaranth 6-8 weeks before moving them outdoors. It’s important to time your seeding carefully in colder climates. Ideally, plant them 6 to 8 weeks before you can move them outside. They will still be small enough to easily transplant at this age, but will be harder to replant if much older.
Move plants outdoors once the threat of frost has passed. Plant your amaranth in a mostly sunny location. In seasonal climates, late May or early June is the best time to transplant seedlings. Replant seedlings about 20 inches apart, in soil that will drain well, and in a location that receives at least 6 hours of sunlight per day. If you did not plant seeds indoors early in the season, you can sow seeds directly outdoors once you’re sure there will not be another frost.