Those tiny black flies hovering around your favourite indoor plant can be incredibly frustrating. Fungus gnats seem to appear out of nowhere, but in reality they’re usually telling us something important. Almost every time, the issue comes back to watering and potting mix.
At Harmony, we focus on correcting the cause rather than just treating the symptom. When you understand why they’re there, they’re actually quite simple to manage.
.
Why Fungus Gnats Appear
Fungus gnats thrive in moist conditions. Their larvae live in the top few centimetres of damp potting mix where they feed on organic matter and occasionally fine root hairs. If the surface of the soil never has a chance to dry out, it becomes the perfect breeding ground.
Watering Is the Key
Most cases of fungus gnats begin with overwatering. Many indoor plants prefer to dry slightly between drinks, yet it’s easy to fall into the habit of watering on a schedule instead of checking the soil first.
Allowing the top layer of potting mix to dry before watering again interrupts the breeding cycle. When the surface remains constantly damp, it creates ideal conditions for larvae to develop. Ensuring pots have proper drainage and that plants are not sitting in water also makes a significant difference. Healthy roots need oxygen just as much as they need moisture. When soil stays wet for too long, root health declines and pests take advantage.
In many cases, simply adjusting your watering practices can dramatically reduce the problem within a couple of weeks.
It’s also worth being cautious with heavily discounted or clearance houseplants often seen in large retail stores. If plants have been sitting in wet conditions for extended periods, the potting mix may already be carrying fungus gnat eggs. Bringing those plants home can sometimes introduce the issue before you even realise it.
Potting Mix Matters More Than You Think
The quality of the potting mix plays a huge role. Dense, compacted or poor-quality mixes hold too much moisture and limit airflow around the roots. This creates stagnant conditions that fungus gnat larvae love.
A premium, free-draining houseplant mix with good structure allows excess moisture to move through the pot while still holding what the plant needs. The surface dries more evenly and roots remain healthier. If a mix smells sour, feels heavy or stays wet for days, it may be time to repot into fresh media.
Often, a simple repot into a quality mix is enough to reset the system.
Natural Control Options
Once watering and soil are corrected, there are several gentle, non-chemical ways to bring populations under control. Sticky traps help capture adult gnats before they lay more eggs and are a simple monitoring tool as well. A pumice-based top dressing such as gnat barrier granules forms a protective layer on the surface of the soil, discouraging egg laying and preventing larvae from emerging.
Neem oil used as a soil drench can target larvae while also supporting plant recovery, and food-grade diatomaceous earth lightly applied to the surface helps dehydrate larvae naturally. Even a light dusting of cinnamon can assist in suppressing fungal activity in the top layer of soil.
The key is that these methods work best when combined with corrected watering and quality potting mix. Products alone won’t solve the issue if the soil remains constantly wet.
The Harmony Approach
There is no magic quick fix. Healthy soil conditions create healthy plants, and healthy plants are far less attractive to pests. When watering is balanced and the potting mix is right, fungus gnats struggle to establish themselves.
If you’re unsure what’s happening with your indoor plants, bring in a photo or have a chat with us in store. We’re always happy to help you work through it naturally and confidently.
Good soil, sensible watering and a considered approach make all the difference.