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Tips for Getting Rid of Fungus Gnats on Indoor Plants

I’ve battled tirelessly with these relentless invaders, trying everything to get rid of them.

Fungus gnats. Those tiny flying pests that seem to love our cherished indoor plants.

I’ve battled tirelessly with these relentless invaders, trying everything to get rid of them. But only one method truly worked for me, and I’ll share this with you shortly.

But first, let’s take a look at the most promising methods out there, so you have a good idea of the available options.

The Fungus Gnat Problem

I first noticed these tiny insects flying up into my face as I watered my houseplants. After some digging, I discovered they were fungus gnats, laying eggs in damp potting soil.

When I first noticed the fungus gnats, I didn’t think much of them. They were tiny and seemed more annoying than harmful.

But as the infestation grew, I began to see the damage they were causing to my beloved houseplants.

Fungus Gnat damage | Pest control

The larvae of the fungus gnats were the real culprits. These tiny, transparent worms feed on organic matter in the soil, including the fine root hairs of plants.

I noticed that some of my plants started to wilt and lose their vigor. Upon closer inspection, I found that the roots were damaged, looking thin and weak. The gnats were literally eating away at the foundation of my plants.

With the roots compromised, the plants were unable to take up nutrients and water effectively. I saw the leaves turning brown and yellow, and the growth of new foliage seemed stunted.

Recognising the serious threat these tiny pests posed to my plants, I realised that understanding their life cycle was essential to finding an effective solution.

Let’s take a closer look at the life cycle of fungus gnats and why this is key to controlling them.

The Life Cycle of Fungus Gnats

Fungus gnats have a life cycle that consists of four main stages: egg, larva, pupa, and adult.

Understanding each stage can help you target the gnats more effectively.

1. Egg Stage: Female gnats lay tiny, white eggs in the damp soil of houseplants. These eggs hatch into larvae in just a few days. The eggs are often laid in clusters, so an infestation can quickly escalate.

2. Larva Stage: The larvae are small, transparent worms that feed on organic matter in the soil, including plant roots. This is the stage where they can cause damage to your plants. They live in the soil for about two weeks, feeding and growing.

Fungus Gnat larva | Pest control

3. Pupa Stage: After the larval stage, the gnats enter the pupa stage, where they transform into adults. This stage takes place in the soil, and it’s a transitional phase that lasts for a few days.

4. Adult Stage: Adult fungus gnats are tiny, delicate, black or dark grey flies. They don’t bite or cause harm to humans, but they can be a nuisance. The adults live for about a week, during which time the females lay new eggs, continuing the cycle.

How to Get Rid of Fungus Gnats

1. Sticky Traps

I started with yellow sticky traps, placing them near the affected plants.

Fungus Gnat sticky trap | Pest control

These traps are coated with a sticky substance that catches the gnats as they fly around. They’re easy to use and can be found in most garden stores.

While they caught some adult gnats, they didn’t solve the problem entirely.

2. Apple Cider Vinegar Trap

Next, I tried a homemade apple cider vinegar trap. Mixing vinegar with dish soap, I created a lure for the adult gnats.

The vinegar attracts them, and the soap breaks the surface tension, trapping them in the liquid.

It’s a simple and cost-effective method but as with the sticky traps, it didn’t affect the larvae or eggs in the soil.

3. Mosquito Dunk Containing Bti

The mosquito dunk method seemed promising. A mosquito dunk is a donut-shaped product that contains Bti, a natural bacterium toxic to mosquito and gnat larvae.

I soaked the dunk in water, and the water containing the dissolved Bti was used to drench the soil. I think it did kill some larvae but didn’t eradicate the problem entirely.

4. Natural insecticide

I also tried spraying with a pyrethrin solution. Pyrethrin is a natural insecticide made from chrysanthemum flowers.

I mixed it with water and sprayed the foliage and soil. It killed some gnats but didn’t have a lasting impact.

It’s a common method but requires careful handling and repeated applications.

The Only Method That Worked: Creating a Physical Barrier

After trying all the above methods, I stumbled upon the one thing that worked: creating a physical barrier between the soil and the air.

Using Sand

I added a layer of sand on top of the soil. The sand dried out quickly, containing none of the organic debris the gnats crave.

During intense infestations, I even put a layer of sand in the bottom of my pots, blocking the adult gnats from accessing the soil via the drainage holes.

A note of caution: While effective, this method can trap moisture in your potting mix, meaning it will take longer to dry out. This could be detrimental to some plants, in which case sphagnum moss might be a better option.

Using Sphagnum Moss

I also used sphagnum moss, placing a good layer of it on the soil’s surface and compressing it down a bit.

sphagnum moss | Pest control

Like sand, it acted as a barrier, preventing the gnats from laying eggs.

It also added a decorative touch to my plants and didn’t trap moisture, so it’s my preferred option. As with the sand, I put a layer of this in the bottom of my pots too.

You want to find one where the material is quite fine, so the gnats can’t make their way to the soil. This is the sphagnum moss I used.

The Lasting Impact

This method of creating a physical barrier has effectively rid my home of gnats on multiple occasions. Unlike other methods, it has had a lasting impact.

But why does this method work?

Why This Method Is Effective

This method of creating a physical barrier is effective because it directly targets the gnats’ breeding ground.

By making the soil inaccessible to the adult gnats, it disrupts their life cycle, preventing them from laying eggs that then mature into adults.

Fungus Gnat | Pest control

It’s a simple yet powerful way to control the infestation without using chemicals or complex traps.

How to Prevent Fungus Gnats

Preventing fungus gnats has become a vital part of my plant care routine. Here’s what I’ve learned and practiced to keep these pesky insects at bay:

Let Houseplant Soil Dry Out

I’ve found that avoiding overwatering is key. Fungus gnats thrive in damp soil, so I make sure to let the top layer of soil dry out between waterings.

I’ve learned to feel the soil and only water when necessary, rather than sticking to a rigid schedule.

Use Potting Mix Free from Gnats

This should really go without saying, but I make sure I always use potting mix that is free from gnats.

potting | Pest control

And I’ve also started keeping any extra mix in a closed container to prevent contamination.

This simple step has helped me ensure that I’m not inadvertently introducing gnats into my plants.

Solarise Potting Soil and Compost

I’ve discovered that solarising potting soil and compost is a great way to sterilise it.

By placing the soil in a sealed plastic bag and leaving it in the sun for a few days, the heat kills any eggs or larvae.

I’ve used this method with both store-bought soil and my homemade compost, and it’s been effective.

Monitor Plants Regularly

I’ve also learned to keep a close eye on my plants. Regular inspection helps me catch any signs of infestation early, allowing me to take action before it becomes a major problem.

I look for signs like sudden wilting or tiny flies around the plants.

Triumph Over Fungus Gnats

My journey with fungus gnats has been filled with trials, errors, and finally, success.

While I’ve explored various methods, only creating a physical barrier with sand or sphagnum moss has proven effective.

If you’re struggling with these pests, I hope my experience can guide you to a gnat-free home.

Remember, persistence and patience are key, and finding the method that works for you may take some experimentation. But the joy of healthy, thriving indoor plants is well worth the effort!

Photo of author

Steve Kropp

Based in Melbourne, Steve's passion is vegetable gardening, and he’s been writing about it for almost 5 years. He also loves all things DIY and is always looking for a new project. When not working on his own garden projects or blogging, Steve enjoys spending time with his family, cooking meals with produce harvested from his garden, and coaching his son’s footy team.

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