Alternanthera is a genus of flowering plants in the family Amaranthaceae. It is a widespread genus with most species occurring in the tropical Americas, and others in Asia, Africa, and Australia. Plants of the genus may be known generally as joyweeds, or Joseph's coat. Several species are notorious noxious weeds.
Water the plants often enough to keep the soil from completely drying out. They generally don't need additional fertilizer, but if they aren't growing well, try giving them a shovelful of compost in summer. Cut them back if the mounds start to sprawl or spread open.