The water hyacinth is a very pretty aquatic plant with smooth, glossy green leaves and long, thick stalks. The leaves are round or oval, and can reach a diameter of up to ten inches, with the entire plant growing about a foot tall, although both smaller and larger plants are common. The spongy stalks are filled with air, helping the plant to float, and the fibrous roots hang below in the water. During the summer, water hyacinths produce clusters of gorgeous lilac or blue flowers which resemble those of a true hyacinth.
In some parts of the world, water hyacinths are eaten by people and fed to livestock. Sewage treatment plants will also grow water hyacinths to remove nutrients from sludge ponds. Because they are extremely resistant to disease, propagate easily, and have beautiful flowers, water hyacinths are also sometimes sold as ornamental plants for water gardens. If you keep water hyacinths in your artificial pond, or even in a bucket or tub, make sure to bring them in whenever the water temperature drops below 55° F. To do this, take the plant, stick it in a pail with some mud from the pond or tub, and put the whole thing in a frost-free, light place until the weather warms up. NOTE: These plants are labeled as a noxious weed in many places. It is illegal to possess, propagate, or sell water hyacinths in many southern states, including North and South Carolina, Texas, and Florida. The best way to control the spread of an invasive species is not to introduce it--if you keep water hyacinths as an ornamental, please be careful not to allow them to grow into any natural water systems.
Native to the Amazon River Basin in South America, water hyacinths are believed to have been first introduced to the United States in 1884 at the Cotton States Exposition in New Orleans. Samples of this decorative flowering plant were given to visitors, and whatever was left over was simply dumped into nearby waterways. In only a year, it had taken over the St. Johns River in Florida, and by 1899, the plant had become enough of a problem for Congress to authorize its removal.
Being originally from the tropics, water hyacinths grow best in full sunlight and high temperatures. They reproduce very rapidly, and have been known to double their population in less than two weeks by putting out side shoots that become new plants (although they can also reproduce sexually). Able to survive in basically any kind of slow-moving water, they can float into streams, reservoirs, lakes and rivers. In the United States, as well as in Australia and other countries, a massive effort has been made to control the spread of this aquatic weed, which causes blocked waterways and ecological disruption. Large populations of water hyacinths form mats that cover the surface of the water and can block sunlight to plants and animals below. Decomposition of dead plants causes oxygen depletion, killing native species. Mats of water hyacinths can block shipping lanes, cause increased water evaporation, provide habitat for more mosquitoes than anyone wants, and are in general a big pain in the ass.
Small populations of water hyacinths can be hand pulled from a lake or pond, but typical removal of larger populations includes mechanical, chemical, and biological control. Until the 1950's, mechanical removal of plants, using a special machine that shreds them into teensy little bits, was the most popular method of removal. Now, the U.S. Army Corps of Engineers also uses herbicides and natural predators to control the spread of water hyacinths. Herbicides such as 2,4-D and copper sulfite are often used, but they are toxic to some native species and are only partially effective. Many different kinds of insects and even fish have been introduced in order to control populations of water hyacinths, such as water hyacinth weevils, moths, Chinese grass carp and even fungus, but these are not always effective and are sometimes more harmful than useful. Until a more effective and less expensive method is discovered, this lovely but destructive plant will probably keep spreading.
my own knowledge of aquatic plants