How to Fight Fungus Gnats in Houseplants Without Chemicals
If you are reading this blog, chances are you either have fungus gnats flying around your plants, or tiny whitish fungus gnat larvae roaming around the topsoil of your plants. (Or, likely both!). Ugh….
Adult fungus gnats look like fruit flies, even though they are not the same.
While fruit flies feed on ripe fruit and don’t have a palate for plants, fungus gnats are quite the opposite; they don’t care for fruit, but feed on plants and the fungi that grow on the extra-moist soil around its roots.
Although gnats are less harmful than other pests, it is important to mitigate the infestation before the plant starts to decay.
You are not alone in this fight against the pesky fungus gnat. In-fact, this bug, is one of the most common pests that afflicts houseplant.
Let’s see what causes fungus gnats, how to fight against them naturally and effectively, and how to prevent their return!!
what causes fungus gnats?
There are a few reasons why fungus gnats make their appearance into your home.
It may not be you and your over-watering style.
It could have been an infested plant you unknowingly picked up from a greenhouse.
Or, perhaps it’s a plant you brought into your home after spending the summer months outside.
No matter how those fungus gnats got into your plants and home, now you need to deal with them.
Until you notice them, these pests continue to feed on the “feeder roots” of your plant and the fungi of overly moist top soil.
Soggy soil is their ideal environment to lay eggs and reproduce.
Plants that are overly watered, or pots with soggy soil caused by a lack of proper drainage and aeration, are most likely to be affected by fungus gnats.
In this case, the solution is not as simple as “cutting back watering”. A radical intervention of removing the plant from its pot, discarding the existing soil, rinsing the roots and repotting it in fresh soil is recommended before starting to treat the plant.
Many pests come into the house after spending the summer months outside. It is a good practice to wash your plants leaves and soil, as well as quarantining these plants before bringing them in the home with pesky hitchhikers! Click here to read my Blog on Safely Bringing Plants Indoors.
Here is a lovely spoonful of fungi I removed from the topsoil of one of my fungus gnats infested plants. This is what the pests snack on to survive in addition to the “feeder roots”. Fungi and mold on your plants’ top soil are mostly caused by overly-moist soil, which is either due to over-watering or poor drainage and aeration.
fungus gnats life cycle
Tiny fungus gnats eggs can hatch into larvae in only three days.
They go from larvae to pupae stage in ten days.
Approximately 4 days after that, the pupae will become an adult fungus gnats capable of starting a new cycle!
These tiny pests draw nutrients from the “feeder roots” of the plant, which are the “hair roots” that grow closer to the surface of the soil. These roots are important, as their job is to absorb water, mineral and oxygen.
In addition to feeding on “hair roots”, fungus gnats thrive on fungi that grow on the top soil of overly-moist plants.
Until fungus gnats have extra-moist soil, they will continue to thrive.
Those white “confetti” in the soil are fungus gnats larvae. And in this picture I am about to wash them away under the tap water!!
first steps to take when you find fungus gnats around your houseplants
Before you even start planning your fighting strategy, you need to take action before those fungus gnats infest other plants!
Once you’ve gone through these “first response” steps, you can move onto further treatment.
However, if your plant is not overly watered, and is planted inside a well draining pot with well draining soil, you can skip this part and move straight into the “Natural ways to Eliminate Fungus Gnats” section.
- ISOLATE THE PLANT UNTIL YOU HAVE A PLAN: take your infested plant and move it away from any other plant in its proximity. Those fungus gnats are not great fliers, so they can’t cover a great distance. A different room that doesn’t have plants in it is just fine. Now you can take time to think your next steps; when to repot it and what do you need to buy. Until then, leave your plant far away from the others.
- REMOVE THE PLANT FROM ITS POT AND REMOVE AS MUCH SOIL AS POSSIBLE FROM THE ROOTBALL: Once you have a plan in place, (or at least a new draining pot with fresh soil), you can take your plant near the closest garbage bin and remove it from its pot. Shake as much dirt from the rootball as possible without damaging the roots. Make sure all the dirt goes into the garbage with the pests! If the pot is a cheap, plastic container, toss it, otherwise, wash it thoroughly with warm water and soap.
- THOROUGHLY WASH THE ROOTBALL: Place the rootball under a running tap with room temperature water and rinse off as much soil as possible. This way, you will eliminate the majority of the fungus gnats eggs and larvae still hiding in the dirt or in the roots.
- REPOT IN A DRAINING POT WITH FRESH SOIL: Repot your plant into a draining pot with well draining, fresh soil. I recommend terracotta pots for the majority of houseplants as its porosity allows the soil to dry out faster. I also like to mix perlite with any type of soil I use. Perlite helps adding drainage to the soil mix. (Mix one part perlite to four parts soil). Make sure the pot is not too big for your plant’s roots. The bigger the pot, the more soil it will contain. The more soil, the more moisture it will hold around the roots! Click here to read my Blog on Repotting Houseplants.
But you haven’t won yet!
Adults gnats may still be lingering around.
A few eggs and larvae may have survived the wash, so it’s time to double down and escalate the war against fungus gnats!
Removing your plant from the pot and shaking off as much infested soil as possible, will also give you a good idea on the size of the rootball. The size of the plant is often no indication of its roots size. So pick a pot size appropriate to the roots’ size. Don’t go too big!
Washing and rinsing the rootball is an effective way to eliminate the majority of pests and diseases, as well as decayed roots.
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natural ways to eliminate fungus gnats, (even if you haven't repotted your plant(s)!)
Fungus gnats are not interested on your plants’ leaves.
They feed on “feeder roots” and the fungi on the top soil. The damage is minor, but if left untreated, over-time your plant will start to wilt, have poor growth and discoloured leaves.
It is important to focus on treating the soil.
No leaf solution, whether natural or synthetic, will help you mitigate the issue.
The only treatment above soil that will help fighting fungus gnats, are the yellow sticky traps. These sticky strips will trap the adult fungus gnats.
Synthetic solution such as insecticides, are not effective at treating eggs and larvae. I tried and failed myself. Besides, often, the use of synthetic products are more damaging to your plants than the pest itself.
In the case of fungus gnats, it is critical to eliminate eggs, larvae and adults from your plants. This may take a few cycles since all stages of the gnats life cycle need to be fought to eradicate the issue. You need to be patient and fight from different angles. When you win the fight, you need to make sure you take proper steps to keep those gnats away for good!!!
Only eliminating adults won’t solve the hatching eggs problems. And only eliminating eggs won’t solve the flying adults around your home, which eventually, may go lay eggs on a different plant!! It may take a few weeks to fight fungus gnats, depending on how many plants you have and how early on you catch the pests.
So, here are the best natural strategies that have helped me fight fungus gnats off!
- YELLOW STICKY TRAPS FOR THE FLYING ADULT GNATS: I use these sticky traps a lot! They are very effective at trapping adult fungus gnats. The more adults you trap, the less eggs they can lay. It is important to replace the traps as soon as they are full as there might be a lot of eggs in the soil hatching new larvae. It is important to combine the yellow sticky traps with soil treatments that eliminate eggs and larvae at the same time. The sticky traps alone are only a partial solution. I use the Garsum Houseplant Sticky Traps.
- GROUND CINNAMON FOR THE LARVAE: Ground Cinnamon is my preferred solution because it is way cheaper the Hydrogen Peroxide and I have over 100 plants in my home! Cinnamon is a natural fungicide that kills the source of fungus gnats snack. Killing their food source, will also eliminate the pesky pest! Cinnamon will have a dual action for your plant in this case; it will kill the fungus and mold on the top soil of your plants and will eliminate fungus gnats over time. I buy the Costco size Ground Cinnamon jar and I sprinkle it all over the top soil of my plants infested with fungus gnats and mold. I literally cover the soil with it, to the point you can’t even see the dirt any more. I repeat the application every three weeks all winter long. (In bad cases I alternate the cinnamon application with Hydrogen Peroxide application!)
- HYDROGEN PEROXIDE FOR LARVAE AND EGGS: While Ground Cinnamon kills the source of fungus gnats snacks, it doesn’t completely destroy the gnats themselves. It makes their life miserable, (in addition to a reduced amount of adults flying around, thanks to the sticky traps!). Let’s not forget that some of these bugs are stubborn and can still hide in the dirt and feed on the “hair roots”. In order to double down on the eggs and larvae fight, you need to intervene with Hydrogen Peroxide (H2O2). Simply mix one part Hydrogen Peroxide to three parts water and water your plant by covering the entire top soil. You’ll see and hear a sizzling sound. That is the sound that H2O2 makes when it gets in contact with organic matters, such as gnats eggs and larvae, and any other organic element in the soil. When H2O2 becomes in contact with organic matter, it breaks down into Oxygen and Water, destroying it. The soft tissue of gnats eggs and larvae are destroyed by Hydrogen Peroxide. In order to destroy all eggs and larvae that new adults escaping the yellow sticky traps may lay after the first application, you need to repeat this process three or more times. Do it every three weeks or so, and alternate it with the application of cinnamon.
It does take patience to fight fungus gnats, but it is important that your plant is not over-watered and that it does have proper drainage even when treated with Hydrogen Peroxide and ground cinnamon.
It is important to mention that neither ground cinnamon, nor H2O2 are toxic. H2O2 is safe for both pets and humans.
Yellow sticky trap filled with adult fungus gnats. (Please notice that the white specs in the top soil are not gnats, not mold, but Perlite!)
Ground Cinnamon sprinkled all over the top soil of one of my Thanksgiving Cacti.
HOW TO AVOID FUNGUS GNATS FROM COMING BACK!
You’ve done all the hard work to fight back the dreaded fungus gnats, now you need to make sure it doesn’t come back!
It’s hard for apprehensive plant parents like me, I know! I am guilty too!
Here’s what you need to know in order to avoid fungus gnats.
- Do not water your plants on schedule year round! Plants’ needs change as the seasons change, even if they are kept indoors year round. The change in outdoor light and indoor humidity caused by A/C vs. heat use make a huge difference in your plants’ metabolism. Many plants go dormant in winter as well, needing less water. The best advice I can give you is not to just CUT BACK WATERING!; it’s test the soil with your finger. If the top inch feels dry to the touch, especially during the winter months, when fungus gnats are most common, you know it’s time to water, (although some plant species may need more or less water depending on location, light, etc…).
- Make sure all your plants are planted into well draining pots with well draining soil.
- Discard all standing water accumulated in saucers and over pots two hours after watering.
- Routinely replace the water in your pebble trays, (if you have any).
- Always keep an eye on the top soil for any fungi, mold and pest.
This is like maintenance physiotherapy after undergoing surgery. You won’t recover successfully without doing your physiotherapy exercises. Plants need their physio too after their pest’s intervention!!!
Testing the soil to gauge moisture levels.
Always rinse and replace water in pebble trays. (Pebble trays are used to increase humidity around those tropical plants that thrive in high humidity).
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