The water hyacinth, Eichhornia crassipes, is a botanical two-edged sword. This floating aquatic plant is strikingly handsome, but presents a highly invasive menace in temperate areas. A beautiful tender perennial, the plant is hardy only in USDA planting zones 9 through 11 and is easily killed by even the lightest frost. Water hyacinths proliferate rampantly, so you'll only need one or two of them to quickly populate any pond.
Toss a floating ring such as a hula hoop onto the surface of your pond in full sun after all danger of frost has passed for your area. This will serve as a container for your water hyacinth plants to grow and multiply in. They won't bloom unless they're crowded, and require full sun for best flowering performance.
Add a single water hyacinth plant or a small bunch of them to the center of the hula hoop. New plants will begin to appear in as little as two weeks.
Pull the plant up every two to four weeks. Use sharp shears to trim root tips back an inch or so to encourage more rapid growth.
Remove excess water hyacinth plants if they become too thick for your taste. Grab a single plant at its base and slowly pull it upward. It will easily break loose from the floating mass. Toss it onto your compost heap.
Rake spent water hyacinths from your pond as cold weather kills them. Add to your compost heap. These plants are cheap and not worth the effort required to successfully over-winter them. Plan on purchasing a new one next spring.