They’re one of the most common indoor plant pests but also one of the most annoying! Fungus gnats are those tiny flies you see mulling around your plants that always end up in your face.
The adult flies aren’t harmful to your plant, but the larvae, if left untreated, can start to attack the delicate roots of your plant and cause a slow death to even your most coveted of foliage. The good news is that fungus gnats are easy to control even if you have an infestation threatening your entire collection and sanity!
Here are our tried and true remedies for getting fungus gnats under control once and for all.
Why Moisture Control Is Important When Treating Fungus Gnats
Gnats live in the soil of your plant, where humidity and moisture are in abundance. The eggs could very well be out of sight in the soil when you purchase a plant and then hatch once you get them home, flying all up in your face and multiplying quickly. We also find that they tend to appear more frequently once the temperature drops and soil naturally hold moisture for longer. In their short life (3 to 4 weeks), fungus gnats can lay up to 300 eggs, which will hatch in 4 to 6 days and rapidly expand the population!
So, the first thing to address is your soil moisture. As a rule of thumb for all houseplants, we recommend allowing the top three inches of soil to dry out between waters. And in winter, this can take several weeks, but the most important thing is to first check your soil BEFORE adding water. Checking your soil before adding water will also help you not overwater your plants in general so try to make this a standard practice for all your plants.
It is also essential to make sure that the pot your plant is living in has adequate drainage holes so that excess water can drain away. Never plant into a pot that doesn’t have a hole unless you are a total plant pro!
Once you change your watering schedule, the next step is to treat the fungus gnats that are already living in the soil.
Treating Fungus Gnats With Neem Oil
When the top three inches of soil are dry, we have found a few methods to kill a population of fungus gnats effectively, and the most common one is using neem oil soak. Use a high quality, non-diluted neem oil and follow the guidelines on the pack to do your own dilution. We use Eco Neem Organic Insecticide- Concentrate.
Then repeat the process again in a fortnight if you see any signs of new flies.
Treating Fungus Gnats With Hydrogen Peroxide
A super common household item and fast working on the larvae and adult flies, a 3% hydrogen peroxide can be diluted with water to create a soil soak similar to the neem oil process. Mix 1 part 3% hydrogen peroxide and four parts water (one cup of HP to four cups of water) and spray on your plant’s soil (avoid the leaves) so that the first few centimetres are drenched.
Treating Fungus Gnats With Diatomaceous Earth
Diatomaceous Earth has microscopic shards of silica (a hard, unreactive, colourless compound that occurs as the mineral quartz) that will rip those tiny Fungus Gnats larvae to shreds as they crawl through it. Plus, it will also kill other common houseplant pests like mealy bugs, spider mites or aphids!).
Sprinkle a layer of the powder over the topsoil of your pot plant. Ideally, add when the soil’s surface is dry to the touch—but before your plant is in dire need of watering (soaking up water will make it ineffective).
The best bit is that it is 100% safe to use in the home around food and pets (as long as you get the food-grade version). But we recommend using gloves and a mask to prevent the tiny particles from getting into your lungs cos like any fine dust; it may cause you to sneeze or cough.
Read why we use DE to treat fungus gnats here at Green Assembly. and why we also add it to every potted plant that heads out our doors.
If you have been trying these methods for months but still seem to be losing a grip on them (and your sanity!), then you can go the hardcore method and have a go with some standard fly spray. Spray any flies that you can see buzzing and spray the top layer of soil every few days. We don’t love this method cos God knows what is in those cans of death, but desperate times call for desperate measures!