Kill The Gnats!

A fungus gnat is so small it’s thinner than the width of a quarter. They commonly appear when cannabis plants are watered too often. If you let the top inch of your soil dry out before watering your plants each time, fungus gnats often naturally go away on their own. However, if you have a really bad infestation, it can take weeks of good watering practices before you get rid of all of them unless you also do something to directly kill the bugs and bring down their numbers. Read on to learn how to get rid of fungus gnats on your cannabis plants for good!

Fungus gnat larvae eat fungus or decaying matter and need wet conditions to thrive. It is common for soil growers to overwater their cannabis plants, and wet soil is the perfect home for fungus and decaying organic matter. After fungus has grown (often invisible to the naked eye) or overwatered matter has begun to decay in the topsoil, fungus gnat lays their eggs in the top layer of wet soil.


Warm + wet topsoil = fungus gnats 

These eggs hatch into larvae that look like tiny maggots which only live in the top 2-3 inches (5-8 cm) of soil. The fungus gnat larvae are the culprits which cause damage to cannabis roots.

Make sure you have fungus gnats


Get Rid Of Fungus Gnats Quickly!

  • Yellow stickey traps\Cards
    • fungus gnats love the color yellow and will fly towards it. These yellow sticky cards are covered with a glue that will trap adult fungus gnats, bringing down their numbers.


  • More Airflow!
    • This helps dry out the top layer of your soil, and also helps prevent the fungus gnats from being able to fly around and lay more eggs.


  •   Viniger Trap
    • Mix water. Viniger and dish soap. The adults are attracted to the smell of viniger.


  • Don’t Overwater!
    • Fungus gnat larvae need a warm, wet environment near the surface of your soil to grow.


  • Kill Larvae in the Soil!
    • Add 1″-2″ of Green Sand
    • Try neem oil on the top layer of the soil
    • try Diatomaceous earth on top instead of green sand
    • BT Bacteria – Another thing you can water your plants with is something that contains “BT” bacteria (specifically, Bacillus thuringiensis var israelensis – Mosquito Bit)
    • Hydrogen Peroxide – Use 1 part hydrogen peroxide to 4 parts water (for 3% pure H2O2)
    • avoid overwatering your cannabis plants from now on
    • Keep your sticky yellow cards up until Fungus Gnats are completely gone
    • pathogenic nematodes (Steinernema feltiae)
    • predatory mites (Hypoaspis miles)
    • predatory rove beetle (Atheta coriaria)

Growing Organic? 

The “brute force” methods above (SM-90 or Hydrogen Peroxide) will kill the fungus gnat larvae, but will also kill many beneficial microbes in the soil. You can add beneficial microbes back, but it will take a while for them to repopulate your soil. This problem only really affects organic soil growers. If you’re providing nutrients to your plants with bottled nutrients, you’re already providing nutrients in a way that your plants will be able to use even if the microbe populations are down. In any case, if growing organically, an organic version of bacillus thuringiensis (subspecies israelensis) is the best option for getting rid of fungus gnats.


Why kill fungus gnats?
Fungus gnats can inflict extensive damage to seedlings in houseplants‏, ‏
Gnat’s Larvae helping in the decomposition of organic matter:‏
The larvae feed on plant roots that have sat in drain water too long and are thus rotting ‎and may be attracted to fungus growing in saturated topsoil, ‏
Some fungus gnats are exceptionally hardy, being able to tolerate cold conditions ‎through their possession of antifreeze proteins.‏

Fungus gnat crash course.


This is a Good Video on gnats.


  • No peat moss soil.
  • Perlite on top of soil/top layer
  • Water correctly, let dry out completely
  • A few Mosquito bits on top layer
  • Sand/Greensand on top layer of soil
  • Hydroton on top layer of soil

Here are a few products we carry in store to help you with the fungus gnat problems that may occure. 

neem oil

Dyna-gro Pure Neem Oil

RTU ( Ready to use ) Neem Oil

yellow sticky trap

Yellow Sticky Trap

mosquito bits

Mosquito Bits ( BT )



Down To Earth™ Greensand

Greensand ( top fill )



T-Drops ( amazing )

diatomaceous earth

Diatomaceous Earth


Here is a video on how to use Nematodes.

cheap\free DIY grown gnat trap video. This does not take care of the larva in the soil, this can but a hurt on them but will not fully erraticate them.

How to use Mosquito Bites to kill larva.