Getting Rid Of The Fungus Gnats Among Us

Posted on Jul 30, 2015
Share

While attending the Wellbeing @ Work event last week at BKM, interior designer Jean Young shared with me that she is one of my regular blog post readers and enjoys both our blog and newsletter. Thank you!

She told me about a real problem with her interior plants and asked me to write about it. Of course! I bet there are a lot of you with the very same problem.

You're not seeing spots, you're seeing fungus gnats on your plants.

You’re not seeing spots, you’re seeing fungus gnats on your plants.

Of the six pests (spider mites, mealy bugs, thrip, scale, white fly and fungus gnats) Good Earth Plants deals with on interior plants, fungus gnats are far and above the biggest pain. You may or may not see the other bugs on your plants, but fungus gnats are literally in your face (they’re attracted to the carbon dioxide we exhale).

Have you ever brought houseplants into your home or office, maybe bought them to introduce some nature into your interior spaces, and after a week or so start noticing these annoying little black flying things darting between you and your computer screen? Ugh! You’ve got a case of fungus gnats!

Fungus gnats look like fruit flies or tiny mosquitoes, but they are not related and they don’t bite. They can be introduced from plants that have unsterilized soil (poinsettias can be the worst) or even from cut flowers – especially from the stinky old vase water.

Fungus gnats are found in damp sewer areas, household drains, and wet plant soil. Fungus gnats lay their eggs in moist soil. Their larvae are only one-hundreds of an inch long and nearly impossible to see, until they grow into adult gnats and fly out of the plant soil into your face. They feed on plant roots, leaves on the soil, and decaying plant materials. They are grown in about 10 days.  They will reproduce year round indoors.

All that tender care including watering your house plants is helping cause this problem. If the soil of your houseplants is consistently damp, the fungus gnats will love living at your house. Another cause is the growing media of houseplants. Many types of potting mixes contain materials that retain moisture, and anything that encourages moisture encourages fungus gnats. This is why Good Earth Plant Company buys from nurseries that pre-treat the soil to eliminate possible infestations.

Yellow sticky traps are one good weapon in the fight against fungus gnats.

Yellow sticky traps are one good weapon in the fight against fungus gnats.

So what can you do about these nasty little nuisance gnats? You need to deal with the problem on several fronts.

1.      First, start letting your houseplants dry out between waterings. The top one to two inches should be completely dry. This is one reason why sub-irrigation works well.
2.      Be sure to remove any dropped or decaying plant materials (leaves and roots) which provide food sources for fungus gnat larvae. If you want to check and see if you have them, put several raw potato slices on the top of the soil. After a few days, take a look at the bottom. Do they look chewed? You have fungus gnat larvae in your plants.
3.      To control the larvae, you can put a quarter to a half inch of horticultural sand (NOT playground type sand) or diatomaceous earth on top of the soil. When you water, it will dry more quickly and confuse the fungus gnats that the plant is dry and not a good place to lay any eggs. And if they crawl across the DE, they are literally sliced to death.
4.      Every other time you water, add one tablespoon of liquid dish soap and one teaspoon of white vinegar to the water. Eventually it will kill the fungus gnat larvae.
5.      If you want to speed up the process, you can take the plant out of the pot, remove as much of the soil as possible without damaging the plant, then repot it. Put all the old soil into a sealed bag and throw it away. You can’t use it anywhere else or you will just spread the problem.
6.      You can make your own organic traps to kill the adult fungus gnats. You can fill the bottom of a deep bowl with apple cider vinegar or red wine, then add several drops of liquid dish soap. Put it near your infested house plants. The gnats love it, and will fall into it and die. Replace it every couple of days.
7.      Buy some sticky insect traps, or make your own. Use pieces of bright yellow colored cardboard and spread Vaseline all over them. Put them above your plants horizontally for the best results. Or use the kind of card holder that comes with a plant from your florist. Put the sticky trap in the card holder and stick it into your plant.
8.      Some home gardeners swear by pouring three percent hydrogen peroxide directly into your plant soil. If you have an especially precious or delicate plant, I wouldn’t recommend this as your first choice.

If fungus gnats repeatedly infest your plants, especially in your office, it may be a serious challenge to completely get rid of them yourself. I’ve seen a case where the gnats were coming in through the ventilation system from another office!

If you are the one trying to take care of your office plants, you may want to consider bringing in an interior plant company like Good Earth Plants. Not to turn this into a commercial, but we only use plants from quality growers and our technicians take great care not to let conditions get to the point where fungus gnats can breed easily. If one of our plants gets infested (which doesn’t happen all that often), we immediately remove it so fungus gnats don’t get into the rest of your plants.