An infestation of tiny flying insects around your Monstera is a common problem for houseplant owners. These pests are almost certainly Fungus Gnats, which are small, dark-colored flies from the family Sciaridae. While the adults are mostly a nuisance, their presence signals a breeding cycle that can eventually compromise your plant’s health.
Confirming Fungus Gnats and Their Source
Fungus gnats are frequently confused with fruit flies, but they are distinct pests with different habits. Adult fungus gnats are slender, mosquito-like insects measuring about two to four millimeters in length. They are typically found walking across the soil surface or flying weakly near the plant; disturbing the soil will cause a small cloud of them to rise up.
The entire life cycle, from egg to adult, takes about four weeks, but the most damaging stage is the larvae. The larvae are translucent, legless maggots with distinct black heads, and they reside almost exclusively in the top one to three inches of soil. These larvae feed on fungi, decaying organic matter, and, when populations are high, the delicate root hairs of the Monstera, which leads to stunted growth.
The root cause of an infestation is consistently damp soil, which is the perfect environment for fungus and decaying matter to grow, providing food for the larvae. Female gnats are attracted to this moist environment to lay their eggs. Eradicating the larvae in the soil is the only way to break the breeding cycle and achieve a permanent solution.
Treating Adult Gnats (Quick Reduction)
Adult fungus gnats do not directly feed on the plant, but they are responsible for laying the next generation of eggs. Reducing the adult population prevents further egg-laying, which slows the growth of the infestation. This step is a temporary measure and must be paired with methods that target the soil-dwelling larvae.
The most effective physical method for capturing adults is the use of bright yellow sticky traps. These traps are highly attractive to the gnats and should be placed horizontally onto the soil surface or vertically near the plant. Simple homemade traps can also be used: fill a small dish with apple cider vinegar and a few drops of dish soap, then cover it with plastic wrap poked with small holes. The gnats are lured in by the vinegar but become trapped by the soap-reduced surface tension of the liquid.
Eradicating Larvae in the Soil (The Core Solution)
Eliminating the larvae stops the reproduction cycle entirely. Since the larvae live just below the surface, the treatment must be a soil drench applied during the regular watering schedule. You can choose from biological control, a hydrogen peroxide drench, or, in severe cases, a complete soil replacement.
The biological control method uses a naturally occurring bacterium known as Bacillus thuringiensis israelensis (Bti), often sold as “Mosquito Bits” or dunks. Bti is a biopesticide that is entirely safe for plants, pets, and humans, but it is toxic to the digestive system of the gnat larvae. To apply, soak the Bti product in water for at least 30 minutes to create a “Bti tea.” This tea is then used to water the Monstera thoroughly. This application should be repeated every seven to fourteen days for several weeks to ensure all new larvae are exposed before they mature.
An alternative, fast-acting method is a hydrogen peroxide drench, which is effective due to the immediate chemical reaction it causes in the soil. Mix one part of standard household 3% hydrogen peroxide with four parts water. Pour this solution over the soil as a normal watering, ensuring it saturates the top few inches. The mixture will fizz as the peroxide encounters organic matter, rapidly breaking down into water and oxygen. This process kills the soft-bodied larvae on contact without harming the Monstera’s roots.
For an overwhelming infestation, replacing the soil is the most extreme measure to ensure removal of all eggs, larvae, and pupae. Carefully remove the Monstera from its pot and gently brush away all the old soil from the root ball. Rinse the roots with room-temperature water to remove any remaining larvae. Repot the plant into a fresh, sterile potting mix, making sure to clean the old pot with a mild bleach solution before reuse.
Long-Term Prevention and Monstera Care
Preventing a recurrence of fungus gnats relies almost entirely on modifying watering practices to eliminate the moist surface soil that attracts them. The Monstera prefers to dry out between waterings, which naturally starves the fungus gnat larvae. Allow the top two to three inches of soil to dry completely before watering again.
To maintain a dry surface layer, consider applying a passive barrier after the soil has dried out. A one-inch layer of decorative sand or food-grade diatomaceous earth (DE) placed on top of the soil creates a hostile environment. DE is composed of sharp, microscopic fossil shards that physically damage the gnat larvae and emerging adults as they attempt to cross it. Since DE must remain dry to be effective, it is necessary to reapply it after watering.
Ensuring the Monstera has proper drainage is also a long-term preventative measure. Always use a pot with unobstructed drainage holes, and immediately empty any water that collects in the pot’s saucer. Switching to a bottom-watering method, where the pot absorbs water from a tray below, is another strategy. This method keeps the top surface of the soil dry while hydrating the roots.