A: This is tough because there are so many plants with this name. Do you have ‘Joseph’s Coat’ amaranth (Amaranthus tricolor)? If so, it is a tall, eye-catching annual, usually grown from seed. There is a rose named ‘Joseph’s Coat’ due to its bright red, orange and yellow flowers.
My guess is that you have common Joseph’s Coat (Alternanthera ficoidea). It is a perennial plant in the tropics but it is treated as an annual in Atlanta. It is typically used as a garden bedding plant. Individual plants grow six to twelve inches tall and twelve inches wide. You can bring a few plants indoors each winter and root cuttings to stock your garden next spring. Three-inch long cuttings stuck in a pot of damp sand root readily when placed in a sunny window.