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Floating pond plants are often beautiful looking, delicate plants. The fact that they don’t stay in one spot, but rather move freely on the water surface, adds to their attraction. Their movements are solely determined by the wind and flow of the water.
These aquatic plants can help to shadow your pond, particularly when there are no trees or other structures which provide shade. By reducing the amount of sunlight hitting the water, floating pond plants help to reduce algae, which need the UV for their growth. They also reduce algae by outcompeting them for the nutrients solved in the water.
Smaller plants often serve as food for water birds or bigger fish, such as koi. Floating pond plants also provide cover for fish eggs, fry or smaller fish.
But floating water plants have their downsides too. Most of them reproduce very quickly. Instead of only being dependent on pollination, they achieve their rapid reproduction by propagating via offshoots or by bigger plants splitting up into two new plants. Because of their high reproduction rate, they are often considered invasive species outside their native habitats.
Adverse side-effects of this severe overgrowth are a reduced gas exchange at the air-water interface. A large number of floating pond plants on the water surface not only blocks the sunlight from algae but from reaching submerged water plants too. These plants then can no longer produce oxygen, which has negative implications for your fish. When this condition lasts too long, your immersed water plants eventually die, and the water gets saturated with sludge gas. This toxic environment will ultimately kill off your fish and will leave you with a pond which seems lively at the surface, but is essentially dead below.
In your garden pond, you can control their growth manually by using a scoop or spoon net and dislodging excessive plants when needed. If you have bigger fish, such as koi carps or goldfish, they might feed on your floating plants – thus reducing their numbers naturally. Using chemicals to kill off your floating plants should always be considered as a last resort. You have to be very careful not to harm your other plants or fish. Additionally, the dead plants will sink to the bottom of your pond and start fouling the water.
Another possibility to control these plants is by using non-hardy varieties. Of course this only works, when you live in an area with cold winters. Plants from warmer climates won’t survive the winter, which puts a natural end to their propagation. But again, you should scoop out most of the plants manually before frost sets in. Otherwise, the dead plants will start fouling, creating a toxic environment for your fish to overwinter in.
So when adding floating plants to your pond, we would strongly recommend you stick to varieties native to your area. They are often dispersed to new waters by water birds. Their roots or offshoots can stick to the feet or plumage of these birds and are then carried away to new sites.
In many countries, some floating plants are considered as pests or at least as a nuisance. Particular plants are even banned from sale in certain countries. In the descriptions listed below, we give indications to the natural habitats of the plants. If you are still unsure which floating plants are best suited for your pond, seek advice from a local wildlife agency or an established gardening expert.
Advice on floating water plants
When released into the wild outside their native range, they can often outcompete native aquatic plants and cause havoc with the natural ecological balance.
Please use only native or non-invasive species in your garden pond!
List of Floating Pond Plants
Nonhardy Floating Pond Plants which won’t survive Winter Frost
Azolla caroliniana forms a symbiotic relationship with a special kind of cyano bacterium (Anabaena azollae). These bacteria are able to fix nitrogen. This ability to collect large amounts of nitrogen lead to Carolina mosquito fern being used in Asia as a fertilizer for rice fields. When the rice fields are flooded, the fern is released into the water. It’s thick mats suppress weed growth, and once the fields are drained again, the collected nitrogen benefits the rice plants.
It’s a very attractive plant and is used by fish as cover and for spawning. In autumn it will die, but can reproduce through it’s spores in spring time.
Azolla filiculoides, Azolla pinnata
Under optimal conditions, mosquito fern is able to double its mass in a matter of three days. It is able to survive short periods of drought and also frost. But it doesn’t survive a prolonged winter, so it’s considered nonhardy.
It’s native to tropical and subtropical rainforest habitats in South America. But it has been introduced into many other habitats and can now be found in almost all areas with at least a moderately warm climate.
Because of its vigorous growth, it is considered a pest in all countries, to which it’s not native. Because of it’s beauty, it’s a popular pond plant. But I would advise you only consider it when you live in an area with winter frost. It won’t survive a cold winter, which means it’s no ongoing threat to the environment.
Due to its invasive nature, all sales of water hyacinth have been prohibited by the European Union in 2016.
Hardy Floating Pond Plants which can survive Winter Frost
The blooming period is from May until June, but bloom is pretty rare. Usually propagation happens when a single plant grows more than three leaves. At this point it breaks up into two plants. Waterbirds help the duckweed conquering new habitats. The plants stick to the bird’s feet and plumage and are thus transported to new waters.
As the name implies, ducks and other waterbirds often feed on duckweed, as do koi and goldfish. It’s even used commercially to feed livestock, as it’s high in protein.
Apart from the arctic regions, Duckweed can be found on all continents.
Blooming period is from May until June, the flowers bear three white leaves and yellow stamina. In autumn it forms a kind of bud, which splits off the dying plant and sinks to the bottom. In spring these buds rise to the surface again and form new plants.
The common frogbit is native to Europe, but also to parts of Northern Africa and Asia.
In it’s natural habitat it doesn’t propagate as violently as other floating plants. In fact it’s considered an endangered species in some parts of Europe.
In North America, especially in parts of Canada, on the other hand it’s an invasive pest.
Floating crystalwort often occurs together with some lemnia species (duckweed), but when competing for nutrients and light, the duckweed usually wins.
However, nowadays it has spread into Central Europe as well as the British Isles.
It grows to a height of up to 14 in (35 cm). It’s roots can touch the ground, but can also be floating.
Floating pennywort spreads rapidly and can cover the water surface completely.
In 2014 it has been declared an invasive species in the United Kingdom, and in 2016 it has been put on a list of “unwanted species” by the EU. So I would recommend you only consider it, when you live in area to which it’s native.
It overwinters by sinking to the ground and rises again in springtime.
It has a high protein content and serves as food source for koi and goldfish as well as waterfowl.
It grows to long plants of up to 6 feet (2 m) and will spread onto the banks of a water body as well. It forms foot long (30 cm) emergent stems which reach out of the water. In spring (and occasionally in autumn) it bears white-pinkish flowers.
It used to be a popular plant for both garden ponds as well as fish tanks. But once released into the wild, it can create problems because of it’s excessive growth. Both swimmers as well as boat propellors can get entangled in it’s long stems and it clogs pipes and ducts.
Due to it’s invasive nature, sales of Myriophyllum aquaticum have been prohibited in a number of US states as well as in the United Kingdom.
It has beautiful leaves and helps shade your pond. But beware, water lettuce has one of the highest reproduction rates of all floating aquatic plants! If you don’t watch it closely and remove a part of the plants regularly, it can overgrow your pond completely.
In 2012 it has been added to the list of invasive species in the EU.
It is native to Europe and parts of Asia.
There are both male and female plants, but propagation is also possible by runners. In the UK e.g. there are almost only female plants. The leaves are quite brittle, which helps it to reproduce.