Allotment Articles 2.
During photosynthesis all green plants produce a surplus of oxygen that they expire. In the case of pond oxygenating plants the gas is released underwater causing some oxygen to be absorbed by the water as it bubbles up to the surface. Any plant that grows with leaves submerged can be considered an oxygenator. Most of them are weeds in their natural habitats, but some have been cultivated and are now sold for fishponds.
Hottonia Palustris, or the Water Violet is one of the more attractive as it produces a flower which rises out of the water. The leaves are feathery and grow entirely submerged.
Tillaea Recurva is another oxygenator sometimes seen for sale. It is an Australian plant that has very fine leaves and stems growing entirely submerged.
Myriophyllum, or Parrots Feather is sold both as an oxygenator and a marginal because its foliage will grow both in and out of the water, but it can prove a little delicate to grow in this country.
By far the most popular oxygenating plant is elodea that is sold by all aquatic retailers in small bunches. This plant is often fondly termed “Pondweed.” Elodea can be planted, or just thrown into the pond because, when it is sold, the bunches, are often weighted with lead and will sink to the bottom. It grows very vigorously and can get out of hand if left un-pruned, but sometimes fish will eat it as fast as it grows and keep it in check. Koi love it so much that it is impossible to grow it in a Koi pond where there are large fish. In fact it is a very important part of the diet of most fish.
Oxygenating plants do many things for the pond besides oxygenating the water: They also provide shade and shelter for the fish giving them a sense of security from prying eyes, or predators. Perhaps the most important function though, is to help to keep the water clear and sweet. Because they are vigorous growers they take a lot of nitrates out of the water thus preventing algae from growing. It is possible to keep the water in a fishpond clear simply with the use of elodea and no filter, but it does need a lot and it will take time to get it established. Oxygenating plants make a good spawning medium for goldfish that will readily lay their eggs on them. Also a large clump will provide a nursery area for the resulting fry to feed and grow in some degree of safety.
So when you are stocking a fish pond, it is a good idea to add a few bunches of oxygenating plant some weeks before adding fish to allow them to start growing before the fish need them.