Fungus gnats are an insect every plant owner is familiar with. They are tiny black gnats that lay eggs in moist, damp soils. As larvae, they will munch on the fungus in potting soil. The fungus in the soil is beneficial for the plants! It helps to retain and even out moisture and break down organic matter to make it bioavailable to the plant. Because of this, different fungi are often added to potting soils to improve the quality. Some articles will try to scare plant parents into thinking fungus gnat larvae are eating the root hairs of your plants. While that is possible, the amount of fungus gnats needed to cause notable damage to your plants is truly an incredible amount, so this is not a worry to hold. Often, the same sites that claim fungus gnats should be a source of worry are also peddling various remedies and "treatments" that don't actually work to kill off the gnats. Sometimes they do work, but harm the plant in the process when there wasn't harm to begin with. Today, we will bust some common myths, discuss how to effectively control fungus gnat populations, and take a deeper look into why they don't cause the harm you may have been led to believe they do.

Myths

     1. Cinnamon

     Some say cinnamon will dry out your soil to make it inhospitable to fungus gnats and their larvae. Some say the cinnamon will act as an anti-fungal, destroying the gnats' food source, which will starve out the larvae. While the latter is based somewhat in truth, cinnamon does have essential oils contained within it that act as an antifungal, you cannot rely on this to control the insects. There are only some strains of cinnamon that have this quality, but there is no evidence to suggest that when the antifungal properties are applied in or on top of the soil that it will affect the insect population, habit, or even truly their food source. Cinnamon can help stop surface level mold from developing, but there is no research data to suggest it will affect the fungi living inside the soil, which the gnats use for their food.

     2. Hydrogen Peroxide

     Hydrogen peroxide (H2O2) is a stress hormone in plants. When this chemical comes in contact with plant cells, it quickly begins work on destroying the cell walls and membranes. Once through, the hydrogen peroxide will begin to destroy the DNA inside the nucleus. It happens even faster on animal cells, since they lack cell walls. This is why it is not recommended to put peroxide on your wounds anymore! Because this is a stress hormone in plants, they will actively try to rid themselves of this chemical. Nothing grows well under stress, why make the plants worry for no reason?

     3. Bottom Watering

     Bottom watering, when done properly will soak the soil all the way to the surface. Watering, from the top or from the bottom, should always saturate the entirety of the soil, even succulents! Overwatering is not the amount of water that provided to a potted plant, but the frequency. Watering a small amount more often will lead to portions of the soil never drying, which can suffocate the roots, leading to root rot. That always damp soil is also a breeding ground for fungi. Moist soils are also necessary for fungus gnat egg and larvae to survive. Having this always wet pocket will provide the gnats with a forever home! Some soil mixes are extremely chunky and create a poor surface for water adhesion, the process in which water will wick itself to the surface of the soil. These soil mixes should not be bottom watered.

     What do we do to actually control these nuisances? First, it has to be recognized that, that is all they are: a nuisance. Fungus gnats bother humans significantly more than they bother plants. The way they survive is by eating fungi that grows in potting soil during their juvenile state. While it is true that, if food runs low and populations are high, they will start to nibble on roots, the chance of this happening is less than likely. It would have to be such a severe infection that the whole area would have clouds of adults flying through the air. Second, the most common way fungus gnats continue to thrive is due to over watering. Some plants, like ferns, carnivorous plants, and others, require wetter soil. This cannot be helped and fungus gnats are a fact of life as a plant parent with those plants. Allowing plants to dry properly between watering is the best way to treat these little pests. If plants are allowed to dry completely at least two inches down, it will kill both juveniles and the fungus the gnats feed on.

     This does not kill the adults in the area and if you water one pot while letting another dry, the gnats will hop from pot to pot. It is best to let them all dry at once. With no proper areas to lay their eggs, the adults will be the last generation. If you have a plant that requires wetter soil and cannot allow it to dry without risking the health or life of the plant (i.e. sundews, maiden hair ferns) mosquito dunks are an option. Dissolve the dunk in your watering can and apply to the soil.

     You may be wondering about those yellow sticky cards that so many recommend online. Those cards are designed to monitor populations of pests in greenhouses, not attract pests. In greenhouse settings, the cards are square and often have lines marking a 1x1 inch grid. By looking at what insects are trapped and how many on those grid sections, it can be determined how bad an infestation is and if it should raise concern. If the yellow coloration of the sticky cards attracted more of one pest than others, the results would be skewed and treatment plans would not be accurate.

     In summary, the best thing to do for your wallet is to allow the plants to dry. If you need more of an immediate solution, or you do not feel comfortable letting your plant's soil dry 2 inches down, mosquito dunks are the way to go. Yellow sticky cards are not an effective form of control and are intended for monitoring.

Happy growing!

<3 Gina