By: Mary Ellen Ellis
Mosquito fern, also known as Azolla caroliniana, is a small floating water plant. It tends to cover the surface of a pond, much like duckweed. It does well in warmer climates and can be a pretty addition to ponds and other decorative water features. You need to know a little bit of basic mosquito fern plant information before deciding to grow this water plant in your garden.
Mosquito fern gets its name from the belief that mosquitoes cannot lay their eggs in still water covered by this plant. Azolla is a tropical and sub-tropical water plant that resembles moss more than ferns.
It has a symbiotic relationship with blue-green algae and it grows well and quickly on the surface of still or sluggish waters. You are most likely to see it on the surface of ponds, but slow-moving streams may also be a good setting for mosquito fern.
Growing mosquito ferns is not difficult because these plants grow rapidly and easily in the right conditions. They can quickly spread out and form thick surface mats on ponds, and they may even choke out other plants. Also, be aware that they can grow to cover nearly the entire surface of a pond, which can lead to lack of oxygen in the water, resulting fish kill.
On the other hand, this plant provides a pretty addition to a water feature because its delicate leaves begin bright green, but then turn darker green, and ultimately a reddish color in fall.
Mosquito fern plant care is easy. As long as you give it the right environment, which should be warm and wet, this plant will thrive and grow. To prevent it from spreading farther than you want or from covering the entire surface of a pond, simply rake it out and dispose of it.
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Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more resembling duckweed or some mosses. Azolla filiculoides is one of just two fern species for which a reference genome has been published. 
Azolla is considered an invasive plant in wetlands, freshwater lakes and ditches. It can alter aquatic ecosystems and biodiversity substantially. 
Here is a short list: citronella grass, lavender, basil, catmint, rosemary, garlic, bee balm, cadaga trees, cedars, clove, floss flower, lemon scented geraniums, lemon balm, lemongrass, lemon verbena, lemon eucalyptus, lemon thyme, Mexican marigold, nodding onion, pineapple weed, wormwood, pitcher plant, mint, snowbrush, sweet fern, tansy, stone root, tea tree, wild bergamot, and vanilla leaf.
Did you notice how many times lemon appeared in our list of mosquito repellent plants? Lemon is not a scent mosquitoes care for at all. That is why oil of lemon eucalyptus is the number one natural ingredient for store-bought mosquito repellent. But, in your yard, lemon eucalyptus isn't going to work exactly the way it does when it is in a repellent. While mosquitoes will definitely avoid these plants, they aren't going to entirely avoid the areas where these plants are planted.
Another name you may have recognized from our list of mosquito repellent plants is citronella. If you're a fan of citronella candles or torches, you may be inclined to think that buying some citronella grass will be as effective at driving mosquitoes away, but it is not. The reason is that the oils inside the citronella grass need to be released in order to ward off mosquitoes. The same is true of lemon grass. If you have either of these grasses in your lawn, they will not be effective at getting rid of mosquitoes. You can, however, keep a plant pot of this grass and rub it when you come out onto your porch or deck. Doing this will release the oils. And rubbing some on your skill will also help.
It is important to know the difference between citronella grass and the citrosa geranium that is often called the "mosquito plant." When these geraniums are planted next to a deck or patio, they do nothing to keep the mosquitoes away. In fact, mosquitoes are known to land on these plants. You are much better off having some citronella grass around.
If your region is currently in its warm/wet season, you have likely swatted away more than your fair share of the dreaded blood-sucking mosquito. They’re not only annoying–insistent on interrupting your campfire fun and producing extremely itchy bumps–they’re also potentially dangerous, depending on whether contaminated blood has mingled within its body.
What’s worse than enjoying a fine summer evening among your garden, patio, or hardscaped pond area only to be disturbed by these flying fiends?
We’ll help you prepare for next time. Skip the chemicals and grow these mosquito-repelling plants near your happy place.
Basil – Due to its essential oils that are extracted for mosquito repellent spray, simply planting these nearby may help deter mosquitoes.
Catnip – One of the main ingredients in catnip was found to be 10 times stronger than the popular DEET repellent, according to one research study.
Clove – Extract the oil from cloves and apply to skin for a personal repellent.
Garlic – Mince, slice, or grate–then sprinkle around the perimeter of the area to be protected. Or, mix with pleasant-smelling oils to produce a body spray.
Lemon balm – The leaves of this minty herb can be crushed and rubbed on skin to repel mosquitoes. Grow them in your garden for added protection and easy access.
Lemon thyme – Repels for the same reason as many other citrus products: mosquitoes detest the scent.
Peppermint – Plant to repel, but if you do get bit, rub a leaf on your skin to alleviate the itch.
Rosemary – The plant itself will help repel mosquitoes, but its oils can also be used as an ingredient in a spray applied to skin.
Stone root – A mint family plant that is easy-to-grow and can be crushed and boiled to form a mosquito repellent.
Lavender – Not only a repellent, but pretty and aromatic. You can even grow these inside in a sunny windowsill.
Lemon scented geranium – Plant these nearby so that you can easily crush up their leaves to produce a lemony-scented repellent. Sprinkle the crushed leaves around your area.
Lemon verbena – Both the plant and its oils smell like lemon and will ward off mosquitoes. Can be used on skin.
Marigolds – There’s no downside to this scenario: if marigolds fail to repel, instead eat the flowers or use as a colorful garnish. Can be easily planted in a container and moved to desired area.
Nodding onion – This flowering plant has an effective mosquito repellent inside of it. Grind or blend the plant to produce a juice that is safe for the skin.
Pineapple weed – Its citrusy scent is likewise offensive to mosquitoes.
Pitcher plant – This carnivorous plant will literally devour your mosquito infestation.
Sweet fern – Throw some sweet fern into your campfire to clear the surrounding area of mosquitoes. Or, use its oil as a body spray.
Wild bergamot – Can be irritating to skin if used in large quantities, so be sure to dilute with water and do an irritation check first. Recommended for repelling mosquitoes only if the plant already exists in your garden since there are less irritable options available.
Wormwood – Contains a very strong odor. Crush up the leaves and scatter around problem areas.
Cadaga – The scent of the cadaga tree is unattractive to mosquitoes.
Cedar – Its oils are often included in mosquito spray products.
Eucalyptus – This tree’s oils can be created into a gentle, aromatic repellent for your skin.
Tea – Tea-tree oil is a popular repellent its scent is too strong for many bugs to withstand. Although natural, it is toxic if swallowed, and high concentrations can irritate the skin (be sure to dilute).
Lemon Grass – Last but not least. A must-have. The popular citronella oil is derived from lemon grass. Easiest to grow from a mature plant.
For easy-to-grow plants that repel mosquitoes, check out:
Creative Commons Flickr photo courtesy of John Tann.
Great tips. But citronella and lemon grass are two different things. Lemon grass leaves can be used to make tea, while citronella is toxic to be ingested.
I was just going to say that, Agatha – you beat me to it.
Citronella comes from Pelargonium ‘citrosum’ .
Sort of sad. This was the seco9nd article on this Gardening website that I read, and it has an obviously glaring error. Makes me wonder about the other articles…
There are Citronella plants.. we have them offered at our local Pacific NW nursery. I plant them in pots.. pretty large pots.. as they mature to 4 ft. I bring them in the shop for winter.. pretty cool. and it works..
alba faraon says
donald baxter says
Lantana shrub repels mosquitoes effectively.
carmelita e. cruz says
What plants/trees/herbs repel flies. We live in a subdivision near a big poultry. Flies swarm the neighborhood especially during daytime and mealtime.
The nasty smelling disposable fly traps from home depot work great…you fill to the line with water and the sawdust with smelly stuff mixes in the water….hang them away from where you work or sit down wind…be considerate of neighbors as well…they do smell
we have lemon grass, a citronella plant, Rosemary, thyme, mint, basil, marigolds all growing in various places in our yard. Still have those pesky Mosquitos.
Carol Ann says
Greg Langus says
try: cover all water in yard. this is where they are breeding. standing water is an incubator for mosquitoes.
Liwayway M. Engle says
Oregano also repels mosquitoes.
What about Backhousia citradora? Lemon scented mytle.
I’ve tried lavender and marigolds neither of them did me any good
Any recommendations for getting rid of fleas on house pets? Dog goes out a few times during the day, was giving the pill from the vet to get rid of the pests, which works great. But would rather have some type of houseplant to get rid of the pests.
Jo .anne says
You might try giving your dog brewer’s yeast. I use Braggs Nutritional Yeast seasoning, about an eighth of a teaspoon on his food daily. He loves it and it does keep the fleas off.
Hi Kindra ,
The mosquitoes germs can be kill rapidly by the spreading of medicine in a garden with the help of harvest roller and also a proper watering to all the plants of a garden according to the passage of a time which help you to kill the mosquitoes germs in a few days and remember don’t give extra water, because the extra water increase the germs of mosquitos in all the leaves of a tree,so make sure all the water is absorbed to save the plans from the mosquitoes kills ,My suggestion is to take care of plants .
Khushroo Dubash says
Actually Citronella oil is derived from the Citronella plant, and Lemon Grass oil from the Lemon Grass plant. Both plants look very similar.
karen sieg says
does BTI in water work? like in rain barrels and other water storage? I keep rain water all the time and use the dunks thinking they kill the larvae and im helping decrease the population..
does anyone know if this is true? bacillus thuringiensis israelonis I think is proper spelling of what I refer to as BTI
I look for any info regarding its use pro and con. thank you.
Yes, those dunks work to prevent mosquito larvae.
Mosquito fern floats on the water in ponds, sloughs, swamps, ditches, marshes, and still backwaters of rivers and streams. You may also see it stranded on mud by receding waters. A pond covered with Azolla seems to have a severe algae problem. Huge floating mats of this plant can completely cover a pond with a velvety green or purplish-red carpet. In autumn, the overwintering bodies of mosquito fern fall to the bottom of the pond they return to the surface in late spring and summer.
Scattered, mostly in counties bordering the Mississippi, Missouri, and St. Francis rivers.
Mosquito fern is a native Missouri fern, but it can be a nuisance aquatic plant. It can completely cover a pond, lagoon, or slow-moving river, and it should never be introduced from one location to another.
Vegetative reproduction is most common in mosquito ferns, with side branches breaking off and forming new plants. As ferns, they do not flower or produce seeds. Instead, they have a two-part life cycle. Generally speaking the plants we see are called sporophytes, and they produce spores. The spores germinate to become gametophytes, which create eggs and sperm, which unite to become a new sporophyte.
But it’s more complicated than that. Mosquito ferns have what botanists have called an “extraordinarily complex” set of reproductive structures. Most peoples' eyes will glaze over at just the names of these structures: sporocarps, two kinds of spores (megaspores and microspores), plus massulae, sporangia, and glochidia. The gametophytes live within the walls of megaspores, which are rounded at the base and have a triangular cap with 3 saclike floats. Don't worry, we won't quiz you on any of this. You're doing well if you just remember the life cycle is "complicated"!
The name “mosquito fern” arose from the belief that populations can grow so densely on the water surface that mosquitoes are unable to breed. Mosquito fern species in Asia have been used for this purpose, but although it might make it more difficult for mosquito larvae to breathe, it does not completely suppress them.
Mosquito ferns can become overabundant and should not be introduced. In some areas of the southern United States, mosquito ferns have interfered with livestock watering, blocked pump inlets, and affected commercial fishing. Also, because it can fix atmospheric nitrogen, it can enrich the water and encourage overgrowth of algae.
Elsewhere, mosquito ferns of various species have a tremendous value in agriculture. Because water fern species can capture nitrogen from the air and convert it to a form plants can use for nutrition, and because it can grow so abundantly, some species of Azolla are cultured as a “green manure” in rice paddies in southeast Asia. The paddies are flooded and the mosquito ferns introduced. Then, the fast-growing, thick mat of mosquito ferns suppresses weeds, and when the mosquito ferns rot, the nitrogen fertilizes the soil. In China, this practice has been used for more than 1,000 years.
The relatively high protein content of dried mosquito fern inspired feeding studies on using it as a component in commercial livestock feed.
Azolla plants are sometimes used in aquariums. However, it is not as commonly used as duckweed, hornwort, crystalwort (Riccia, a type of liverwort), and several other floating plants that require less light. Remember, never release aquarium plants, fish, or invertebrates into natural waters.
The complex reproductive biology and structures of mosquito ferns can seem either mind-numbingly tedious or intensely fascinating, depending on your perspective. Many people love solving riddles and learning about weird, offbeat, nerdy topics.
Mosquito ferns have chambers in the floating leaf lobes that contain a symbiotic blue-green alga (cyanobacterium), Anabaena azollae. This filamentous organism can fix nitrogen from the air into a nitrate form that can be used as a nutrient by the water fern. The blue-green alga benefits from the protective chamber in the fern, which also provides some mineral nutrients. This is similar to what happens in the roots of legume plants (peas, beans, clover, alfalfa, and so on).
About 49 million years ago, during the Eocene epoch and at a time when Earth’s atmosphere was about 41–46 F higher than it is today, tremendous mats of mosquito ferns apparently “bloomed” in the Arctic Ocean. When the plants sank to the bottom of the sea and were covered by sediment, they took with them large amounts of carbon dioxide, removing it from the global nutrient cycle. This contributed to the formation of Antarctic polar ice sheets and helped to cool the atmosphere to how it is today. Scientists call this the “Azolla event.”
In addition to research on Earth’s climate, there is also currently a lot of interest in exploring the Arctic for oil deposits. Much of this centers around the ancient, buried, fossilized Azolla beds. Burning this petroleum for energy would release the carbon — that the Azolla mats had sequestered millions of years ago — back into the atmosphere.