How to Stop Fungus Gnats From Attacking Your Microgreens

Fungus gnats are the most common insect pest of houseplants. Because microgreens are also grown in the house, they too can be affected by these pesky little insects. This article will explain how to stop fungus gnats from attacking your microgreens. 

fungus gnat infestation

Fungus gnats are tiny, blackish flies that you see flitting around house plants. They are attracted to moist soil.

The adult female fly lays her eggs at the base of the plant in moist soil. When the larvae hatch, they begin to feed on the plant roots.

Both adults and larvae excrete a sticky substance called honeydew that becomes an ideal breeding ground for sooty mold.

Fungus gnats can quickly become a problem in your home if not controlled.

Where Do Fungus Gnats Come From?

Fungus gnats are ubiquitous and seemingly omnipresent.

The gnat eggs can lay dormant in the soil and potting mixes for an extended period.

Garden Center

When buying plants from a nursery or garden center, check for flying insects around the plants before purchasing them.

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The lack of small flying insects around the garden center isn’t a sure thing; as mentioned, fungus gnat eggs can lay dormant. 

It’s best to quarantine any plants separately before bringing them into the house and around your other plants.

Potting Mixes

You can also introduce fungus gnats, their larvae, or eggs into the house in bags of potting soil. 

Home Microgreens does not recommend buying potting mix from garden centers that stock their bagged soil near house plants or tropical plants.

Plants in garden centers and nurseries (especially those sold by box stores) are often overwatered by employees. Overwatered plants attract fungus gnats, which migrate over to the potting mixes and infest the soil through the holes intentionally placed in the bags to reduce moisture and air build-up in the bags.

A side note here. 

The Home Microgreens Potting Mix contains diatomaceous earth (DE), killing fungus gnats and larvae. No commercial brands have this preventive measure. More on this later in the article.

This video talks about why commercial potting soil bags have holes in them and why this is a lousy reason to stock potting soil near plants.

However, fungus gnats are everywhere and very small, so even adhering to those precautions may not stop fungus gnats from gaining access to the home through windows, doors, and screens.

Symptoms of Plants with Fungus Gnats

Flying Insects

Fungus gnats are attracted to light, so you’ll often see them flying around the windows near your indoor plants or flitting about the microgreen lights. 

They’ll quickly and easily invade your houseplants and microgreens if the soil surface is moist. They especially love all microgreens, African violets, geraniums, poinsettias, carnations, and spider plants.

Although not a symptom of the plant, seeing flying insects around your plants is usually the first signal that something is afoot. 

Of course, fungus gnats first infest the unhealthiest plants, but even the most healthy ones will likely be plagued if not controlled.

If you have fungus gnats in your home, you may notice that some or all of your plants are not growing well.

Poor-performing plants are a sign that something is wrong with the root system.  

Fungus gnats can cause problems for plants because they lay their eggs in the soil, and once they hatch, the larvae feed on plant roots.

Moist & Wet Soil

When the soil surface is wet or constantly moist, it brings fungus gnats out of the woodwork. They are very attracted to overly moist soil or decomposing organic matter. 

After all, this is where fungus gnats lay their eggs. 

The best answer for how to stop fungus gnats is not to overwater any of your plants. If possible, water from the bottom and let the water wick up the soil column.

Honey Dew

Plants severally affected by fungus gnats plants will have a sticky sap on the lower portion of the plant stem. This is called honeydew, and it’s a sugar-rich liquid that is extruded from very tiny holes in the plant stem.

The holes are caused by insects feeding on the plants—usually either aphids or fungus gnats. 

Black Sticky Goo

The honeydew then becomes a substrate that black sooty mold spores attach to and start to colonize. Microgreens rarely reach this stage because they grow and are harvested quickly.

The Dangers of Fungus Gnats

Fungus gnats can cause damage to plants, and they can also spread plant diseases. They can also contaminate food and be a nuisance to humans.

What attracts fungus gnats to your plants and microgreens is moist organic matter. The larvae of these flies feed on fungi, and they can cause damage to plant roots. Fungus gnats can also spread plant diseases, such as Pythium and Rhizoctonia

Fungus gnats are a common insect pest on microgreens. They can cause damage to the plants by feeding on the leaves and stems. They can also spread diseases such as damping-off disease to microgreens.

How to Stop Fungus Gnats?

You can do several things to control fungus gnats indoors and save your houseplants and microgreens from this pesky pest.  

Check the Plant for Pests Daily

To check your indoor plants for pests, you will need to: 

  • Inspect your plants’ leaves, stems, and soil for any signs of pests.
  • Look for larvae (the most common insect pests of houseplants) around the base of the plant and on the roots.
  • Remove any pests that you find and dispose of them properly.

If you think your plant has gnats, it is crucial to act quickly to prevent the problem from worsening.

Be sure to check all your plants regularly for signs of pests to catch any issues early on.

Rid Flying Gnats with a Vacuum

If you see fungus gnats flying around your plants, use your vacuum cleaner hose to suck up the insects as they soar around. 

Of course, be careful not to damage your plants. 

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Use Neem Oil on House Plants (only)

This article is about fungus gnats on microgreens, but house plants are the most common source of fungus gnats.

Because we water most house plants from the top, they’re the most likely to become infested with fungus gnats. 

So getting rid of fungus gnats on house plants will protect your microgreens.

Neem oil is a naturally occurring pesticide that you can use on houseplants. 

You can apply neem oil topically to the plant’s leaves or add it to the water. 

When using neem oil, following the instructions on the bottle is essential, as too much oil can damage the plant.

Neem oil is most effective when used on plants not currently flowering, as it can help trigger the plant’s flowering cycle. Once the plant begins to flower, discontinue using neem oil.

Insecticidal Soap

Insecticidal soap often time isn’t strong enough to kill fungus gnats, maybe because there isn’t enough contact time with the active ingredients.

Be careful soaking the soil with insecticidal soap as it can affect the plants too.

But you can try using insecticidal soaps first.

Neither neem oil nor insecticidal soap is recommended for use on microgreens by us. But they can be helpful on infested house plants that may lead fungus gnats toward the microgreens. 

Use Yellow Sticky Traps 

To get rid of fungus gnats, you can use yellow sticky traps. The traps use an adhesive that the gnats stick to when they land on the surface.

The traps will then kill the gnats so they cannot continue breeding and infest your plants. Yellow sticky traps are difficult to find at most hardware or gardening stores.

We use these yellow sticky traps in the garden. The yellow color draws the insects. They come in shapes too. 

Try Diatomaceous Earth 

Diatomaceous earth (DE) is an organic way to control pests. It’s a powder made from the fossilized remains of diatoms. Diatoms are algae with siliceous exoskeletons that, when broken, form tiny, very sharp shards.

These shards puncture the pest’s exoskeleton, causing them to dehydrate and die. A death by 10,000 cuts, if you will.

Apply DE by sprinkling it on the soil around your plants. Adult gnats come into contact with DE when feeding and laying eggs. The DE will also infiltrate the potting mix, where the larvae will contact it. 

Home Microgreens Potting Mix to the Rescue

Home Microgreens Potting Mix contains diatomaceous earth to protect your microgreens! Including it in the potting mix is a preventive measure against fungus gnats.

We think the small cost of adding DE to our potting mix is worthwhile. Even if the house plants have a fungus gnat infestation, your microgreens will be safe from them!

Our Recommendations on How to Stop Fungus Gnats

Be careful to bring new plants home. Take a second at the garden store to stand still and observe if you see any fungus gnats flying around. If you do, don’t buy any plants or quarantine them when you get home. 

We recommend bottom-watering microgreens as fungus gnats are attracted to overly moist surface soil. Keeping the soil’s surface as dry as possible will deter fungus gnats from being attracted to your microgreens.  

Diatomaceous earth is a reliable way to get rid of fungus gnats. It is effective in killing both adults and larvae.

It, too, can be used in the garden when pests are present. 

DE is inexpensive, and a little goes a long way.

Yellow sticky traps are handy in two ways. They can be used to see if you have any insect problems by capturing them as they become present. When you have an infestation, the traps can attract and kill the flying adults.  

Remember to leave them up for a while afterward to catch any late-hatching larvae. 

Note* All treatments mentioned here are nondiscriminatory and will also kill beneficial insects. Again, not an issue in the home, but only use it in the garden when other methods can’t control pests.

Patience and Persistence Beats Fungus Gnats 

If you have a fungus gnat problem, don’t despair. You can get rid of them and protect your plants with patience and persistence.

Using Home Microgreens potting mix containing DE is a great start and preventative measure. 

Bottom watering microgreens and not overwatering any other plants in the home dramatically reduces the chance of a fungus gnat infestation.

If fungus gnats become a problem, use sticky traps and sprinkle DE on the soil to eliminate these tiny pests. 


  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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