HEIRLOOM. Brilliant red seedheads dangle like dreadlocks from the tops of sturdy, 3-5' plants. They hold their color a long time, and are great in arrangements. Plant at the back of a bed with big tropicals like cannas, celosias, ornamental corn or castor bean. Amaranthus needs heat and a long season. Start in containers and set out 6-week plants after frost. The seed is tiny and takes two weeks to sprout.