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Fungus Gnats: A pain for us, but are they really a pain for our plants?

Picture this. You're sat enjoying your favourite Netflix show and BAM! a little black fly comes hovering around your head bumping into your face. Five minutes later, there's another one! And another one!


Is it a bird? Is it a plane? No. It's Sciarid flies, Sciaridae or as they are most commonly called; Fungus Gnats. These clumsy, tiny, but prolific reproducers can quickly spiral from a single digit figure into the hundreds if allowed to thrive. Whilst initially appearing similar to fruit flies, these are very much not the same beast. Whilst fruit flies feed off and make a habitat in overripe fruits sat on a warm counter, fungus gnats, more akin to miniature mosquitoes in their form and shape, call the freshly moistened soil of our favourite houseplants their home.

Breeding all year round, female gnats lay their eggs in the top layer of potting soil, hatching within just a few days in moist and warm soil. The larvae then typically feed on decaying plant material and any fungi that might be present in our soils. Usually, Fungus Gnats are entirely harmless to your plants.


Natural solutions stemming from good practice, plant hygiene and of course prevention should always be the first consideration before chemical intervention (We don't advise boiling water and chemicals out of the kitchen cupboard just yet). Here are some of the teams best tips and practices. Whilst others may exist, these are the methods we regularly use and find the best success with here at WR.

1. Prevention

Prevention has to be of absolute priority, especially when dealing with such an invasive little pest.

  • Gnats love hydrated soil. As such, the go-to answer is allowing the top couple centimetres of soil to dry out. This creates a less habitable home for gnats and can prevent the development and hatching of already laid eggs. If your plant likes to stay moist, try watering the plant from the bottom to prevent a moist top layer.

  • Preventing the gnats from getting to the soil in the first place can be a great line of defence. Subsequently, we have found dressing the soil surface with a inorganic top layer can create a physical barrier, which under the right conditions can also smother the eggs. This can be done easily with gravel, pebbles, glass or our personal favourite: Shell on Earth recycled whelk shells. It is important that the dressing is fine enough to create an effective barrier and the material used should ideally be sterile (so maybe leave the stones from the bottom of the garden where they are!).

2. Non-chemical interventions

  • Cinnamon is not just for chai lattes. It is a great effective anti-microbial, anti-fungal and anti-bacterial spice which makes a great natural pesticide. Sprinkling this spice liberally over the soil surface works by naturally destroying the food source for the gnats, further making the soil more inhospitable to them.

  • Sticky fly papers, although we aren't the biggest fans of single use plastics, do work. By sticking them into the pot they immobilise and eventually kill any gnats caught out by them. This prevents the mating and in turn further egg laying of the gnats caught which can help massively to curb the population.

3. Chemical interventions

Sometimes the infestation can become so intense that we are unable to keep on top of it using the above methods alone. As such pesticides can at times be our last line of defence.

  • Many pesticides exist, but we are particularly keen on the SB Plant Invigorator and Bug Killer. It works as an immediate physical bug killer whilst also containing a good mix of nutrients for the plant.

We hope these tips can help you to get on top of your fungus gnat problems, or at least stop worrying so much about them. The good news is whilst these bugs are a pain to us but for our mature happy houseplants they typically pose little to no actual threat to the plant's health.

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