What are those pesky insects that hover around your indoor garden and cover the soil of your favorite plants?
If you looked very closely, you’d see they resemble tiny mosquitos, but at 1/8th of an inch in size, their characteristics are not easy to distinguish. They are fungus gnats, and they love houseplants.
In this article, we will examine the best way to get rid of fungus gnats and why they got to your plants in the first place.
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What are fungus gnats, and why are they attracted to houseplants?
Fungus gnats are tiny insects about the size of a fruit fly. Unlike the fruit fly, though, they are not attracted to certain smells or products, but to moist soil and decaying organic material in plant pots.
The adult fungus gnat can lay up to 200 eggs near the surface of the soil; the hatched eggs become larvae which burrow into the soil to feed on fungi in the soil.
In two weeks, the adult fungus gnat emerges and repeats the cycle. Although adults only live for about a week, it’s easy to see how 200 eggs per adult can quickly become an infestation.
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As annoying as these insects are, the adult fungus gnat does not pose harm to either animals or humans. They do not bite or carry diseases. But, if their numbers grow too large, the larvae will begin to feed on the fine root hairs of your plant. This will damage the plant, especially young plants.
Fungus gnats are also known to carry a pathogen which infects the roots of seedlings, called ‘damping off,’ and causes young roots to weaken and die, killing the young plants.
In houseplants, fungus gnat damage can be seen in a slowing down of the plant’s growth and lower leaves turning yellow and dropping off.
Depending on the severity of the infestation, plants can completely wilt and die. Some plants, such as geraniums, African violets, and spider plants seem to be particularly susceptible to fungus gnats. However, any plant sitting in wet soil can be a victim. Yet another reason not to overwater our plants!
How can I prevent fungus gnats in my plants?
Fungus gnats are attracted to moisture and decaying organic material. An overwatered plant, especially one with dead leaves or stems lying in the pot, is a prime target.
Dry soil discourages the fungus gnat from laying its eggs. So, in addition to careful watering and the removal of dead leaves, indoor gardeners should always use potting soil designed for indoor plants.
Outdoor garden soils will often be mixed with peat moss or compost, and these organic materials will attract fungus gnats.
To ensure proper drainage, you can add perlite or vermiculite to their potting soil, which presents less welcome environments for fungus gnats. Besides, a ½ inch layer of sand on the top of the soil will keep the soil dry and stop the gnats from laying their eggs.
How to get rid of fungus gnats
If, after all your best efforts, you notice that some of your plants are infested with these common houseplant pests, there are many ways to deal with the problem.
Fungus gnats only fly for very short distances so if you find an infested plant, separate it from your other houseplants. You may decide to re-pot if the infestation is severe. Sometimes changing the top 2 inches of soil and allowing it to dry will do the trick.
Be sure to remove any standing water under the plant. Once these things are done, there are several ways to either trap the gnats or treat the soil to make it inhospitable to the insects. Most effective is a combination of treatments which will attack the adult gnat and the larvae.
Using these treatments for four weeks will ensure that two generations of the pest are affected.
Products to get rid of fungus gnats
To start, let’s look at some products which are easily available that will attack both the adult gnat and the larvae. It is not necessary to use harsh chemicals or insecticides, as several natural products are handy.
1. Neem Oil
Neem Oil is an organic pesticide derived from the neem tree. It contains a compound (Azadirachtin) which inhibits plant pests. This product should be used as a “plant drench,” meaning diluted with water and used to soak the soil as well as a spray for leaves (especially the undersides) and stem.
By drenching the soil, the plant will absorb the pest killing compound and distribute it throughout the plant system. Many Neem Oil products are available on Amazon.com, including the well-reviewed Neem Bliss Pure Neem Oil.
Although there are many producers of Neem oil, there is an advantage to using cold-pressed neem oil. The compound Azadirachtin in Neem oil tends to degrade with heat, so cold-pressed oil has more potency.
Mix the oil with water and a small amount of dish soap liquid. Repeat the treatment as needed, and make sure to apply it in the morning or when the plant is not in direct sun. Also, neem oil does have a strong odor which some people find unpleasant.
Watch this short video on applying Neem Oil for some useful tips:
2. Diatomaceous Earth (food grade)
Diatomaceous Earth is a natural product that is non-toxic to humans and animals.
It contains mineralized fossil dust, and its abrasive nature works well on disabling fungus gnats. Even though this product is not harmful, it is wise to use a face mask when applying it.
You can spread it on the top of the soil and on the stems of the plant. However, make sure the soil is dry before adding the product. Diatomaceous Earth works best when there’s a layer of sand on the top of your plant’s soil. It’s also a good idea to mix it right into your potting soil to prevent insects.
There are many brands of Diatomaceous earth available, as it helps control many types of pests, in the garden and the home. The best-reviewed brand on Amazon.com is Harris Diatomaceous Earth Food Grade.
The following video shows how to apply diatomaceous earth and has great ideas for keeping topsoil in your plants dry!
3. B-TI Bacillus thuringiensis israelensis
B-TI is a naturally occurring organism which targets fungus gnats, mosquitos, and black flies, affecting their stomach lining and effectively killing them.
It is harmless to humans or animals and is approved for organic gardening and farming as it’s not absorbed by plants and leaves no residue.
Keep in mind that using B-TI is somewhat slower method than those mentioned above. Also, it needs to be re-applied every couple of weeks until the infestation disappears.
Mosquito Bits is one of the products that contain B-TI and has a fantastic effect on keeping the fungus gnats in check.
To kill the fungus gnats, sprinkle the bits on the top of the soil and water the plant. For a more powerful effect, add some Mosquito Bits in your watering can before watering the plants and let it sit for 5-10 minutes.
Check out this video for more info on how to use Mosquito Bits:
4. Hydrogen Peroxide
An effective way of attacking fungus gnats larvae is to spray diluted 3% Hydrogen Peroxide on plants and the soil.
Hydrogen Peroxide is a standard household product that also has many uses in the garden.
To treat fungus gnats, mix hydrogen peroxide with three parts water and, once the soil is dry, use it to water your plants.
Again, it is essential to repeat this treatment to ensure that all generations of the pest are affected.
The following is an informative video on the many beneficial uses of Hydrogen Peroxide in the garden:
5. General Hydroponics GH2045 AzaMax
AzaMax is a natural product derived from Neem oil which contains the same active compound of Azadirachtin and gets rid of fungus gnats by starvation and growth disruption.
It is very highly rated by Amazon customers who suggest spraying this product weekly, diluted with water, on all plants to prevent any insect infestation.
You can dilute it by adding 1 oz of AzaMax to 1 gallon of water or if you want a stronger formula, by adding 2 oz to 1 gallon.
Also, some people use this product as a way to immunize the plants and avoid infestations.
6. Beneficial Nematodes
Nematodes are microscopic roundworms which provide a biological control of houseplant insects.
The nematodes release a bacterium that’s not harmful to humans or pets, but which is fatal to fungus gnats and other pests. Products such as Nema Globe Pot Popper sell nematodes in packets, several million per package.
The nematodes placed in the soil and slowly released to live and feast on gnat larvae.
One satisfied Amazon.com customer suggests installing the nematodes, watering the plant, and then covering it with a plastic bag. This way, the fungus gnats won’t be able to escape.
Nematodes can even be kept in your refrigerator for up to two weeks (if you don’t mind the idea of worms in your fridge!!)
7. Growstone Gnat Nix
Growstone Gnat Nix is another chemical-free product.
Gnat Nix is a gravel-like product made from 100% recycled crushed glass.
The glass is ground, milled, and baked and provides a physical barrier when added to the top of the plant soil.
It’s easy to use, keeps the gnats away, and has an attractive appearance on your houseplant soil!
8. Katchy Indoor Insect Trap
We would be remiss if we did not mention electric traps as many people swear by them to reduce flying insects in their homes.
The Katchy Indoor Insect Trap can be plugged into either a wall socket or USB port and attracts insects by its UV light.
Once the insects hover over the light, a fan sucks them into the trap, where they are stuck on glue boards or ‘sticky discs.’ This electric trap works best in a darkened room. Depending on how many fungus gnats you have, you may have to replace the sticky discs frequently.
While this product is excellent for ridding the air of fungus gnats, it does nothing to address the actual problem of why they are there in the first place. As we have seen, both adults and larvae must be attacked to free our houseplants from infestation.
DIY Methods to Get Rid of Fungus Gnats
Before purchasing the products mentioned above, you may wish to try some do-it-yourself ways of catching and eradicating fungus gnats in your plants. To attack both adult gnats and the larvae, combining some of these methods can be very effective.
I. DIY Traps
1. Yellow Sticky Traps
There are several ways to catch the adult fungus gnats. Yellow sticky traps are sold everywhere and, similar to flypaper, are covered in glue.
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Fungus gnats are drawn to the yellow color. It is easy to make a homemade gnat trap by obtaining some yellow card stock, smearing the sides with Vaseline, and placing horizontally on your plant soil. By placing horizontally, you will trap gnats both coming and going!
2. Apple Cider Vinegar
A common way to trap fungus gnats is to partially fill a small jar with apple cider vinegar and a drop of dish soap, cover it with jar lid or plastic wrap that has small holes in it and place near your infested plants.
The gnats will be attracted to the scent of the liquid, enter the jar, be unable to get out and drown.
Here’s an easy how-to video:
3. The Potato Slice Method
A potato slice placed on the soil of your plant will also attract fungus gnats.
After about four hours, the underside of the potato will be covered in gnats (yuk!).
Replace it with a new slice.
II. DIY Attacking Larvae
As we have learned, attacking the larvae of fungus gnats is essential to halt the infestation.
4. The Sand Method
It is a good idea to cover plant soil with about a half-inch of sand to avoid fungus gnats from penetrating the soil to lay eggs.
Sand absorbs water quickly, and since gnats like moist environments to lay eggs, they will avoid sand. New gnats will also be unable to emerge.
The plant will have to be watered from the bottom to keep the sand on top from washing away.
5. The Steel Wool Method
Place a thin layer of steel wool over the soil of infected plants.
Fungus gnats will be unable to fly into the soil, and mature larvae will be unable to fly out.
To ensure that several generations of larvae are annihilated, leave the steel wool on for at least four weeks.
Fungus gnats are a nuisance and are unwelcome visitors to your indoor garden. But as we can see, there are numerous ways to address this problem; it’s good to know that the use of harsh chemicals is not required.
Attacking a fungus gnat infestation with natural or even common household products is an environmentally friendly way of bringing out the best in your plants.
Have you tried any of these methods to get rid of these pests? What about other ideas, like using cinnamon or chamomile tea?
It would be great to hear your experience in dealing with pests in your houseplants.