How do I get rid of fungus gnats?

If you spot tiny flies buzzing around your houseplant(s), there is a good chance they are fungus gnats. These flies, also known as sciarid flies or fern gnats, look a lot like fruit flies, but instead of going for your fruit they go for your beloved houseplants. You will want to solve this quickly, of course, but it is just as important to know how to keep fungus gnats away in future.

Preventing fungus gnats

Fungus gnats are drawn to very damp soil and rotting organic matter. They lay their eggs in these conditions, sometimes as many as 200 at a time! So it is crucial not to let your plant's soil get too wet and to make sure no water is left standing in the pot. Rotting or permanently wet soil is paradise for these annoying flies. Taking good care of your plant and making sure the pot drains well is therefore essential.

How do I get rid of fungus gnats?

Have these pests set their sights on your houseplant anyway? Then getting rid of them is the only answer! Follow this step-by-step plan and your green friend will soon be back to its old self.

1. If you keep several houseplants together, it is important to isolate the plant with the eggs from the others. Not sure which plant the flies are in? Give all the plants a little water and watch carefully to see which one the flies rise from. If you cannot find the affected plant this way, move the plants further apart as a precaution.
2. Let the plant's soil dry out and give only the bare minimum of water. You do not want your plant to die of thirst, of course.
3. Stand a glass of red wine next to the plant, because fungus gnats are strongly drawn to it. Once the adult gnats are trapped in the red wine, they can no longer lay new eggs.

There are two ways to tackle the larvae. The first is to use nematodes: tiny worms that you simply pour into the potting soil. Nematodes are natural enemies of fungus gnats and will eat the larvae. Once the larvae are gone the nematodes die off, and the problem is solved.

Not a fan of tiny worms? Then you can give the plant fresh potting soil instead. This comes down to repotting your houseplant, but you put it straight back into its familiar pot. Make sure as little of the old potting soil as possible comes with it, because that reduces the chance of any fungus gnat eggs being left behind.

How fungus gnats spread

Fungus gnats spread easily over long distances in search of the right conditions to breed. This happens both through the larvae, which move towards new food, and through the adult flies, which actively look for somewhere to lay their eggs. Because they are so mobile, they can quickly reach other plants or other rooms in your home, which is why it is important to step in quickly when you have an infestation. Stopping them from spreading is just as important as getting rid of them.

Help! The fungus gnats are back

Fungus gnats can return after treatment, often after a while. That usually happens because the care the plant gets has not changed. Fungus gnats are attracted to damp potting soil, and that is often down to how much water you give your plant. So once you have got rid of them, it is essential to adjust your watering. Give less water than before and let the soil dry out properly between waterings, so the conditions never become attractive again.