How to get rid of gnats or flies in office plants

It’s a question people have been asking for as long as there have been plants in offices - how to prevent, and get rid of pests?

First, let’s start with why we get flies in plants in the first place. We’ll also explain why planting companies like us don’t usually have issues with flies.

After that, we’ll dig into what we do about them if we find them - hopefully this will help you sort your fly problem, too!

Flies in indoor plants, particularly in office environments, are usually fungus gnats. These small, black or dark brown flies are attracted to moist soil and organic material, making indoor plant pots an ideal breeding ground.

1. Moist Soil:

Fungus gnats lay their eggs in moist soil. Overwatering indoor plants creates a perpetually damp environment that encourages their reproduction.

2. Organic Matter:

These flies feed on decaying plant material, algae, and organic debris in the soil. If your potting soil is rich in organic matter, it provides both food and a breeding site.

3. Indoor Conditions:

Offices typically maintain stable temperatures, which are ideal for fungus gnats. The lack of natural predators indoors also allows them to thrive.

4. Improper Drainage:

Poorly draining pots or soil that retains water can lead to stagnant moisture, creating an even more suitable environment for their growth.

5. Introduction from New Plants or Soil:

Flies can enter through infested soil or newly introduced plants. Egg-laden soil from a garden centre or store can bring the problem indoors.

So now you know what causes flies in your indoor plants, we can have a look at how to get rid of them.

Here are our maintenance technicians give their top tips on how they tackle flies when they're out and about - it's a combination of preventative measures and active treatments.

1. Control Watering

Let the Soil Dry Out: Reduce watering frequency to let the top 2-3 cm of soil dry out completely. Fungus gnat larvae cannot survive without moisture.

Use Well-Draining Soil: Replace heavy, moisture-retaining soil with a mix that drains better, such as soil with sand or perlite.

2. Use Yellow Sticky Traps

Place yellow sticky traps near the plants. These traps attract and capture adult fungus gnats, helping to reduce their population.

3. Apply Beneficial Nematodes

Beneficial nematodes, such as Steinernema feltiae, are microscopic organisms that feed on fungus gnat larvae. Mix them into the soil as per the manufacturer's instructions.

4. Top-Dress the Soil

Add a layer of inorganic material (e.g., sand, diatomaceous earth, or small pebbles) to the top of the soil. This prevents adult flies from laying eggs and disrupts the life cycle.

5. Introduce Biological Controls

Introduce natural predators like Hypoaspis miles (predatory mites) or Bacillus thuringiensis israelensis (a bacteria toxic to larvae) into the soil.

6. Replace the Soil

If the infestation is severe, repot the plant using fresh, sterile soil and a clean pot. Dispose of the old soil carefully to prevent spreading the infestation.

7. Use Hydrogen Peroxide Solution

Mix a solution of 3% hydrogen peroxide with water at a ratio of 1 part peroxide to 4 parts water. Use this solution to water the plants. It kills larvae in the soil but breaks down into water and oxygen, leaving no harmful residue.

8. Improve Office Conditions

Reduce Humidity: Use a dehumidifier to lower humidity levels.

Increase Airflow: Place fans near plants to make it harder for fungus gnats to fly and reproduce.

9. Avoid Standing Water

Empty saucers or trays under pots regularly to prevent water accumulation, which attracts gnats.

10. Natural Deterrents

Add cinnamon powder to the soil surface. Cinnamon has antifungal properties that can inhibit the growth of fungi that attract gnats.

So, how do plant companies like us deal with flies? It all starts with phytosanitary screening, a rigorous process designed to prevent the spread of pests, diseases, and invasive species that could harm local ecosystems or agriculture.

The process begins with pre-screening and inspections before import. At the port of entry, plants undergo another detailed visual inspection for signs of pests (e.g., insects, eggs, larvae) or diseases (e.g., mould, spots, or wilting). If anything raises concern, the shipment is quarantined, and if deemed unsafe, it is destroyed to prevent contamination.

Once the plants reach our facility, they are thoroughly inspected again, and routine pest control measures are implemented. If pests are found, we address them using appropriate methods, such as fumigation or biological controls like nematodes or natural predators, depending on the type of pest.

After installation at your space, the focus shifts to proper care, particularly watering. Ensuring plants are watered correctly—not too much and not too little—plays a significant role in preventing flies. Additionally, we use vulcaponics as a substrate. While not completely impervious to pests, this innovative growing medium reduces their chances of thriving and helps us regulate watering more precisely.