As an Amazon Associate, I earn from qualifying purchases. This means I may earn a small commission if you purchase through links on this page, at no extra cost to you.
How to Get Rid of Fungus Gnats: A Comprehensive UK Guide
Before we get into this, we recently shared an article on how to get rid of fungus gnats using just sand and yellow sticky traps.
Fungus gnats can be a nuisance for plant enthusiasts and gardeners alike. These tiny flies thrive in damp soil, laying eggs that hatch into larvae capable of damaging plant roots. Tackling fungus gnats effectively requires a combination of preventative measures, natural remedies, and targeted treatments. Here's how to handle them, with a focus on UK-specific methods and products.
Understanding Fungus Gnats
Fungus gnats are small, dark flies often mistaken for fruit flies. They are common pests for plant enthusiasts, thriving in moist, organic-rich soil. Their lifecycle, from egg to larvae to pupae to adult, makes them persistent and tricky to eliminate. As I write this, I’m dealing with an infestation myself, which has given me firsthand insight into their habits and how to fight back effectively.
The Life Cycle of Fungus Gnats
Eggs: Adult female gnats lay their eggs in moist soil, typically close to decaying organic matter. Each female can lay 100-300 eggs over her short lifetime (7 - 10 days). These eggs are tiny, white, and nearly invisible to the naked eye, making early detection challenging. They hatch within 4–6 days under favourable conditions, such as a warm and humid environment—something we often provide for houseplants during winter in the UK.
Larvae: Once the eggs hatch after 4 - 6 days, the larvae emerge as small, translucent worms with black heads. This stage lasts for about two weeks. During this time, they feed on decaying organic material in the soil. However, if the organic matter is insufficient, they may start nibbling on plant roots. This can weaken plants, stunt growth, and make them more susceptible to diseases.
Pupae: After the larval stage, fungus gnats enter the pupal stage, which lasts around 3–4 days. They form cocoons within the soil, preparing to emerge as adult flies.
Adults: The final stage is the adult gnat, a small fly about 2–4 mm long. Adults do not damage plants directly; their role is to reproduce and lay the next generation of eggs. They live for about one week, during which they mate and restart the cycle.
Why Is Understanding Their Life Cycle Important?
The key to controlling fungus gnats is interrupting their lifecycle, for example:
Egg Stage: Drying out the soil can prevent eggs from hatching, bottom watering can help with this.
Larval Stage: Using nematodes or hydrogen peroxide kills larvae in the soil. Diatomaceous earth can be helpful for killing them too as it cuts into their skin. Neem oil can stop larvae from pupating due to interfering with their hormones.
Pupal Stage If you're using nematodes or hydrogen peroxide for the larvae, these treatments can also target pupae.
Adult Stage: Yellow sticky traps catch adults before they lay eggs, reducing the population.
By addressing multiple stages of their life cycle simultaneously, you can eliminate infestations effectively.
Prevention Is Key
You likely are reading this article as you already have fungus gnats, however, by putting these prevention measures into place you can reduce their numbers and stop them from coming back.
Manage Watering: To avoid fungus gnats from thriving, you are supposed to allow the top few inches of soil to dry between watering as fungus gnats thrive in consistently moist soil. They seem to thrive in my dry soil too so it's not clear to me how much of a difference this makes. If this is something you would like to achieve you can get watering globes which promote deeper watering or bottom watering.
Improve Drainage: Use a well-draining mix with added perlite or sand to reduce water retention.
Cover Soil: Add a layer of horticultural grit, sand, or decorative pebbles to deter gnats from laying eggs.
I have over 30 houseplants which meant that I had to try many approaches and had mixed success. The one thing that I can say is that using sand to top my plants and sticking a yellow sticky trap in each pot and at the top of windows really did stop these little guys in their tracks, within about 3 days I had seen the numbers of these flies reduce drastically.
How to Get Rid of Fungus Gnats
Adult Fungus Gnat Killers:
Yellow Sticky Traps: These are highly effective at capturing flying adults. Simply place the traps near infested plants, under grow lights or at the top of windows fastened with sticky tape. In the UK, sticky traps are available at most garden centres or online stores and are affordable and easy to use. These have been super effective for me and have caught over 100 gnats each, it's important to change them when you notice gnats not getting stuck to them any more, this can especially be an issue in bathrooms.
DIY Vinegar Traps: Combine apple cider vinegar with a drop of washing-up liquid in a shallow dish. The gnats are drawn in and drown, make sure your vinegar is fresh though as otherwise it will not attract the gnats.
You: Okay, so you're going to be be going round in circles if you're trying to rid these guys yourself, but if you see them in the air you are best to 'clap' them or if you see them on a wall you can squash them, or for a mess free alternative wet your finger and touch them as they will stick to you, then discard them. Fly squatters are of limited use as these flies are so small.
Fungus Gnat Larvae Killers:
Biological Control with Nematodes For Fungus Gnats: Beneficial nematodes are natural predators of gnat larvae. They are mixed with water and applied to the soil, where they target and destroy the larvae. I have not tried these myself but looking online it's clear they are popular, just expensive.
Neem Oil Treatment: Spray the soil surface with a diluted neem oil solution. Neem oil disrupts the lifecycle of the gnats, making it harder for the larvae to progress. I would like to note that it smells odd and whilst I believe that it can impact them did not do anything noticeable to reduce my numbers.
Hydrogen Peroxide Drench: Mix one part hydrogen peroxide with four parts water and pour it into the soil, this kills larvae on contact while being safe for plants. This has seemingly worked well for me as since I have done it there are less fungus gnats, however, it only works on the first contact so is of limited use in winter when you are not regularly watering plants.
Cinnamon Powder: This is great as it targets fungus in the soil which means the larvae starves with no food source. Just be sure to use a sprinkle to avoid overdoing it, you can also mix an amount into compost when potting which can avoid future fungus growth. If you can get it from the supermarket in the world food section this is usually cheaper than the glass jars, you can also use the link to buy in bulk, it's good in cookies and hot drinks too!
BTIs: Bacillus thuringiensis israelensis (BTI) is a natural bacterium used to control fungus gnat larvae in soil. It releases toxins that specifically target and eliminate larvae without harming plants, pets, or beneficial insects. Easy to apply via granules or liquid, BTI is an eco-friendly solution for managing gnat infestations effectively. This is usually effective in the soil for around 48 hours so just like the hydrogen peroxide it will be useful to combine with other methods.
Diatomaceous Earth (DE): Sprinkling a thin layer of food-grade diatomaceous earth on the soil surface can help. This natural powder is made of fossilised algae and damages the exoskeletons of larvae, leading to dehydration. It’s safe for plants but should be kept dry to remain effective.
Cooking the soil: Often when you buy compost it will already have fungus gnats in some stage of their life cycle. Before using the compost, it is an idea if you do not have hydrogen peroxide to treat the soil with boiling water or by baking it. I recently did the boiling water trick and I can't imagine there were any survivors, that soil was HOT!
Repotting Plants (Good for eggs and cocoons as these are harder to rid):
If the infestation is severe, repot your plants with fresh, sterile soil, ensuring to sterilise the old soil (by cooking as above)or fully remove it. Wash the pots thoroughly to remove any lingering eggs or larvae. I find white vinegar good for this as it cuts through dirt nicely and fungus gnats are not fond of the smell.
Do I need to buy a full armoury to get rid of fungus gnats?
Look, you've come here looking for a solution to your fungus gnat problem and I've given you too many options. I strive to cover everything possible and fungus gnats through their various stages of life cycle can be tricky tenants.
For me, the most effective all-rounders for controlling fungus gnats across their full life cycle are sand and yellow sticky traps. This is because the sand stops the fungus gnats from laying eggs in the soil and the flies from emerging from the sand if well packed enough. The yellow sticky traps then take any gnats out the air which stops them from finding new damp places to lay eggs.
Together, these two treatments form a powerful, low-maintenance strategy for keeping fungus gnats under control throughout their lifecycle, from egg to adult.
If money is not a constraint and you don't mind partaking in various methods then any of the other options are worth doing, fungus gnats are prolific so the more you can do to tackle them the better.
Final Thoughts on Tackling Fungus Gnats in the UK
Fungus gnats may be small, but they’re certainly a big nuisance for houseplant enthusiasts, especially in the UK where our indoor environments are perfect breeding grounds. Understanding their lifecycle—from egg to larvae to adult fly—is key to managing and preventing these pests. By focusing on interrupting their lifecycle at each stage, you can significantly reduce their numbers and protect your beloved plants.
Effective treatments include using yellow sticky traps to capture adult flies, applying sand to disrupt egg laying, and using solutions like hydrogen peroxide or neem oil to disrupt their development.
Prevention is just as important as elimination, so consider managing your watering, improving drainage, and covering the soil with grit or sand to keep fungus gnats at bay.
With patience and a combination of solutions, you can enjoy your plants without the buzzing nuisance of fungus gnats!
We have plenty more articles on these little fungus gnats on our site.
Comments