How To Get Rid of Fungus Gnats From Your Houseplants

Fungus Gnats...those pesky flying bugs that are the stuff of nightmares for all indoor plant lovers, setting up camp around your indoor plants.  Super annoying but not uncommon.  And it doesn't make you a bad plant parent either!

If you're suffering from an infestation, here is all the info to get them to buzz off for good.

 

WHAT ARE THEY, AND WILL THEY KILL MY PLANTS?

In short, Fungus Gnats (gnats) are those tiny flying midgie looking bugs which you might see hovering just above the soil of your plants.  The adult gnats (the ones flying around) are more annoying than anything, and won't directly cause harm to your plants.  BUT they lay eggs in the soil, which hatch into larvae.  These little critters feed on things in the soil, including plant roots, which may start to do a bit of damage over time if the infestation is left to get really bad. 

CAUSES

  • Overwatering - this is the number one culprit.  Always check the top 5cm (at least) of soil is dry before watering.  Use a moisture metre for best accuracy.
  • Leaving water in drip trays under your plants - make sure you remove any excess water from drip trays after watering.
  • Soil doesn't dry out quickly enough - this is especially common in Winter, when soil takes a long time to dry in the cooler weather.
  • Insufficient light - also impacts on how long it takes for soil to dry, as well as the overall health of your houseplant.
  • Decaying leaves or other plant matter around the base of the plant - remove and discard dying and dead matter immediately. This is important plant hygeine.
  • Soil or potting mix - unfortunately, fungus gnats may already be present in the soil or potting mix you bring home from the nursery.  Unless you see the flying adults when you open up the bag, it is impossible to tell until you've potted up your plants and the adults emerge.  Yep it really sucks, but it does happen!  They can also find their way into opened bags of potting mix that have been inappropriately stored. 

SOLUTIONS & TREATMENTS

A word of warning before we get into the nitty gritty.  Don't expect overnight results.  You need to treat all stages of the gnat life cycle, and this can take a little time.  Your patience and committment will be rewarded though, so don't give up!

  • Adjust your watering regime:  adult gnats can only lay eggs in damp soil, so over-watering or leaving pots sitting in water is a sure fire way to get them breeding.  Reduce your watering frequency and allow at least the top 5cm of soil to thoroughly dry out between drinks. If your soil is taking a long time to dry, move your plant to where it receives more light and warmth (especially during Winter).
  • Sticky traps: you may have seen these at your local hardware store.  Sticky traps will attract (they apparently like the yellow colour) and trap the flying adults and help reduce their numbers.
  • Apple cider vinegar: put some in a shallow dish near your plants; the bugs will fly to it and drown.
  • Soil barriers:  commercially available gnat barriers and diatomaceous earth are brilliant soil barriers which can be put on the top layer of soil or mixed in the top few centimetres of soil.  The shards of silica within the diatomaceous earth will deter adult gnats and prevent them from laying eggs in the soil.  If eggs are already present in the soil, the shard of silica in the diatomaceous earth will kill them after they hatch. 
  • Neem oil: you need to get rid of the larvae in the soil, and one of the best ways of doing this is a soil drench. Prepare your pure neem oil as per the packet instructions to get the dilution ratio correct (and avoid killing your plant). Then you can either soak your whole pot of soil in the solution, or deeply water your plants with it until the excess drains from the bottom of the pot.  This will kill the eggs and larvae no matter where they are in your soil.
  • Repeat treatments: you may need multiple treatments for a few weeks until your infestation is under control.  Remember that you must treat each life cycle stage, so using multiple treatment methods is recommended.

 

Time to get to it!  Happy gnat hunting!