Water hyacinth, Eichhornia crassipes, is a popular water garden plant that floats freely on the surface and is noted for its striking blue-violet flowers. It grows successfully in all areas of a pond or container garden, and is so fast-growing and prolific that it requires periodic thinning. This rapid growth has turned water hyacinth into a weed species in many Southern states and in temperate parts of California since it was introduced in New Orleans from Brazil in 1884.
A floating perennial that grows up to 3 feet tall, water hyacinth features a rosette of waxy leaves attached to spongy, inflated petioles that help keep the plant afloat. The water hyacinth is named for its dramatic, hyacinth-like central flower stalk. Beneath the water’s surface are branched, dark fibrous roots. Connected by floating stolons or horizontal stems, individual plants soon form vegetative mats that can move in any direction, propelled by wind or water currents. Under ideal growing conditions a population can double in size and mass in 10 to 14 days.
Water hyacinths are native to the Amazon River Basin and thrive in warmer waters. They do well in both ponds and container water gardens as "floaters," or unattached water plants with trailing underwater roots. Killed by frost, water hyacinth has spread widely due to mild winter conditions throughout the South and in California. In natural aquatic habitats it competes aggressively against native plan species and can cause oxygen depletion and fish kills.
Water hyacinth has been a popular ground cover in sunny U.S. water gardens for generations. As floaters, water hyacinths move freely on the surface of the water and can grow in all areas of the pond, adding the element of constant change. By shading the water, they reduce the light available to support algae growth. Roots and other underwater parts of aquatic plants provide habitat for invertebrates both large and small, which help feed fish and amphibians, reptiles and ducks. When water hyacinth and other plants die, their decaying vegetation feeds aquatic invertebrates.
Once escaped from domestic cultivation, water hyacinth can quickly overrun a waterway or aquatic system. Such domination displaces native plants needed for food or shelter by wildlife, damages or destroys fisheries and degrades waterfowl habitat by reducing areas of open water. Water hyacinth obstructs navigable waterways, blocks irrigation and drainage channels, and clogs boat propellers, water pumps and hydroelectric generators. Standing water in mats of water hyacinth are ideal breeding sites for mosquitoes.
You can control overgrown populations of water hyacinth by physical removal or containment within floating barriers. Research conducted by the University of Florida has established that white Chinese geese, noted for their exceptional weeding abilities, can effectively control ponds of water hyacinth. Foliar sprays of glyphosate herbicides are also commonly used. Water hyacinth can’t be sold in states where it’s classified as an invasive species. In Texas, it’s even illegal to possess or transport it.