Money Tree Gnats: How to Get Rid of Them for Good

Fungus gnats infesting a money tree are almost always a moisture problem, and the fastest way to get rid of them is to let the top layer of soil dry out completely between waterings while simultaneously targeting the larvae already living in the potting mix. The adults are the tiny flies you see hovering around the pot, but the real infestation is underground, where larvae feed on organic matter and fine roots. Killing the adults alone does nothing lasting because a single generation can complete its entire life cycle in about 25 days, meaning new waves keep hatching from eggs you cannot see.

What You Are Actually Dealing With

The small dark flies circling your money tree are almost certainly dark-winged fungus gnats in the family Sciaridae. The most common species found on houseplants are Bradysia impatiens and Bradysia coprophila, both of which thrive in the moist, organic-rich potting mixes used for tropical plants like Pachira aquatica (the money tree).¹ Adults are only about two to four millimeters long with dark bodies and translucent wings. They are weak fliers, so they tend to stay close to the soil surface and rarely wander far from the pot.

Adults live for just a couple of days, but in that short window a female can lay dozens of eggs in the top centimeters of moist soil. Under typical indoor temperatures, eggs hatch in roughly three to four days, and the larvae spend about 17 days feeding before pupating for another two days and emerging as new adults.² That means a full generation turns over in under a month. If conditions stay favorable, generations overlap, and you can end up with larvae, pupae, and adults all present at once, which is why a small problem snowballs so quickly.

Why Money Trees Are Prime Targets

Money trees are tropical plants that like consistent moisture and are typically sold in peat-heavy potting mixes. Both of those traits are exactly what fungus gnats look for. Female gnats are drawn to lay eggs in soil that is microbially active, and peat-based mixes tend to host plenty of microbial life, especially when kept damp.³ Lab research has shown that fungus gnats are attracted to and stimulated to oviposit by a wide range of living microorganisms growing in soil and around plant roots.⁴ In other words, a healthy, biologically active pot of soil is attractive to gnats. That is a frustrating paradox for houseplant owners: good soil is gnat-friendly soil.

The other big factor is volatiles released by fungi and decomposing organic matter. Some fungal scents actually repel certain gnat species from laying eggs in already-colonized compost, which suggests the gnats are reading chemical signals in the soil to find ideal spots for their offspring.⁵ The practical takeaway is that overwatering your money tree does not just keep the soil moist; it keeps the surface layer biologically active and chemically appealing to egg-laying females.

The Real Danger Is Underground

Adults are a nuisance, but they do not bite or feed on your plant. Larvae are the problem. They chew on fine root hairs and organic debris in the potting mix, and in heavy infestations they will damage the root system enough to cause wilting, yellowing leaves, and stunted growth. For a money tree, whose braided trunk and root zone are already sensitive to rot, larval feeding is more than cosmetic.

Even more concerning, fungus gnat adults and larvae can carry plant pathogens from one pot to another. Adult gnats have been shown to transport Fusarium, a fungal pathogen that causes root and stem rot, from infected plants to healthy ones.⁶ They also carry other soilborne pathogens like Verticillium and Thielaviopsis on their bodies, and because adults can fly between pots, a gnat problem in one plant can spread disease to others nearby.⁷

This matters specifically for money trees because Pachira aquatica is susceptible to stem rot caused by Pythium splendens.⁸ And fungus gnat larvae have been demonstrated to vector Pythium species to plant roots, with transmission rates reaching as high as 65 percent in lab conditions for one particularly aggressive strain.⁹ Transmission dropped dramatically when potting mix was present rather than bare filter paper, so real-world rates are lower, but the risk is not zero. If you have a gnat infestation and your money tree starts developing soft, dark spots at the base of the trunk, the gnats may have introduced a pathogen.

Step One: Cut Off the Water

The single most effective thing you can do is let the top two to three inches of soil dry out before watering again. Money trees tolerate brief dry periods much better than most people assume, and larvae cannot survive in dry soil. Eggs laid in the top layer will desiccate, and newly hatched larvae will die before they can reach wetter soil deeper in the pot. This alone can break the breeding cycle within one to two generations.

If your money tree is in a pot without drainage holes or is sitting in a saucer that collects water, fix that first. Standing water under the pot creates a permanent wet zone at the bottom of the root ball, which is exactly where larvae love to feed. Empty saucers after watering and consider switching to a pot with better drainage if the current one retains too much moisture.

Some people try bottom-watering (placing the pot in a tray of water and letting the soil wick moisture upward) as a gnat strategy. The logic is sound: the top layer stays dry, which discourages egg-laying. This works as a preventive measure, but it will not kill larvae already present deeper in the soil. Think of it as a helpful complement to the other methods below, not a standalone fix.

Monitoring So You Know What You Are Fighting

Yellow sticky traps are the standard tool. Place a small card just above the soil surface, and it will catch adults as they fly around the pot. This tells you whether the population is growing or shrinking, which is the only way to know if your efforts are working. Gnats are drawn to the yellow color, and adding a small green LED light to the trap catches even more.¹⁰ For a single money tree on a windowsill, a plain yellow sticky card is plenty.

For monitoring the larvae underground, a surprisingly effective trick is to press a thin slice of raw potato onto the soil surface and check it after a couple of days. In greenhouse research, potato discs proved to be a reliable method of monitoring fungus gnat larvae compared with yellow sticky cards, because the larvae are attracted to the potato and feed on it.¹¹ If you flip the slice and see tiny translucent worms, you have an active larval population.

Killing the Larvae in the Soil

Drying the soil disrupts the cycle, but if you want to actively kill larvae that are already established, you have several options that actually work.

Bacillus thuringiensis israelensis (Bti)

This is the gold standard for home use. Bti is a naturally occurring soil bacterium that produces proteins toxic to the larvae of flies and mosquitoes but harmless to plants, pets, and people. Products sold under names like Mosquito Bits or Gnatrol contain Bti and can be mixed into the water you use for your money tree. In lab tests, exposing fungus gnat larvae to Bti from egg to pupa dropped survival to around 8 percent, compared to 84 percent in untreated controls.¹² Soak a handful of Mosquito Bits in your watering can for 30 minutes, then water the plant with the treated water. Repeat every time you water for at least four to six weeks to catch overlapping generations.

Beneficial Nematodes

Steinernema feltiae is a microscopic parasitic nematode that seeks out fungus gnat larvae in the soil, enters them, and kills them within a couple of days. Greenhouse trials have shown that applying S. feltiae at standard rates significantly reduced fungus gnat larval populations in potted plants including poinsettias and impatiens.¹³ You can buy these nematodes online. They arrive as a powder or gel that you mix into water and pour over the soil. The soil needs to be moist (not bone dry) for the nematodes to move, so apply them on a watering day. They are harmless to earthworms, plants, and animals.

Predatory Mites

Stratiolaelaps scimitus (formerly Hypoaspis miles) is a tiny soil-dwelling mite that eats fungus gnat larvae. It reproduces successfully on a diet of fungus gnat larvae alone.¹⁴ In mushroom cultivation, releasing these mites into growing media significantly reduced fungus gnat populations to levels that growers considered non-damaging.¹⁵ For a single houseplant, a small sachet of predatory mites sprinkled on the soil can provide ongoing control. The mites are invisible to the naked eye and stay in the soil, so there is no “ick factor” for most people.

Neem Oil and Other Home Remedies

Azadirachtin, the active compound in neem oil, does have insecticidal properties against fungus gnat larvae. Lab testing has confirmed that it affects development time and emergence rates in Bradysia impatiens, with the effect varying by temperature and growing substrate.¹⁶ Diluted neem oil soil drenches are popular among houseplant hobbyists, and the evidence supports that azadirachtin can slow larval development, though it is less immediately lethal than Bti. If you prefer a more “natural” approach, neem drenches repeated weekly can reduce the population over time, but they work best alongside the watering changes described above.

Cinnamon is another remedy that circulates on social media. Cinnamon oil does contain cinnamaldehyde, which has demonstrated insecticidal activity against mosquito larvae.¹⁷ However, sprinkling ground cinnamon on your potting soil is not the same as applying concentrated cinnamon oil to standing water. The concentrations involved in kitchen-grade cinnamon are far too low to have a meaningful impact on larvae living inches deep in moist soil. It may have a mild antifungal effect on the soil surface, which could make the surface slightly less attractive for egg-laying, but I would not count on it as a primary treatment.

Hydrogen peroxide soil drenches (typically a mix of one part three-percent hydrogen peroxide to four parts water) are another common suggestion. The idea is that the peroxide kills larvae on contact. There is no peer-reviewed evidence specifically testing this against fungus gnats in potted plants, so I cannot point you to hard data. Anecdotally, many growers report success, and the chemistry is plausible: dilute peroxide fizzes in the soil and breaks down into water and oxygen, which could suffocate or damage soft-bodied larvae. It will not hurt your money tree at that dilution, so it is a reasonable thing to try, but do not rely on it as your only strategy.

What Does Not Work as Well as You Would Hope

Diatomaceous earth (DE) is often recommended for fungus gnats. The idea is that a layer of the sharp, desiccating powder on the soil surface will kill larvae and deter egg-laying. In practice, it disappoints. Researchers found that both dry and moist layers of diatomaceous earth generally did not prevent adult emergence or egg-laying. The dry DE absorbed moisture from the growing medium below, expanded, and cracked, creating fissures that larvae crawled through without difficulty.¹⁸ If you are already using DE on your money tree’s soil, it is not doing harm, but it is probably not doing much good either.

Sand topdressing is a related approach: a half-inch layer of coarse sand on the soil surface makes it harder for females to reach the moist organic layer where they want to lay eggs. Sand does not crack the way DE does, and some growers swear by it. The limitation is that sand only protects the surface. If the pot already has an active larval population deeper in the soil, sand will not kill them. Use it as a preventive layer after you have dealt with the existing infestation, not as a cure.

Putting It All Together

The most reliable approach combines cultural change with one active treatment. Start by extending the time between waterings so the top soil dries out. Place a yellow sticky card near the pot to monitor adult numbers. Then choose either Bti drenches or beneficial nematodes to kill larvae already in the soil. Bti is easier to find at garden centers and hardware stores; nematodes may need to be ordered online and used quickly since they are live organisms. Either one, paired with drier watering habits, should bring the population under control within two to three life cycles, roughly six to eight weeks.

If the infestation is severe and the money tree looks unhealthy, consider repotting. Remove as much of the old potting mix as possible, gently rinse the roots, and replant in fresh, well-draining mix. A blend with perlite, bark, and some peat rather than straight peat will hold less surface moisture and give the roots better aeration. This physically removes the larvae and pupae living in the old soil and gives your money tree a clean start.

Preventing Gnats from Returning

Once you have cleared an infestation, a few habits keep it from recurring. Water only when the top inch or two of soil feels dry to the touch. Money trees are more drought-tolerant than most tropical houseplants, and erring on the dry side protects against both gnats and root rot. If you bring home a new plant, quarantine it away from your money tree for a couple of weeks and check for gnats before placing it nearby. New nursery plants are one of the most common ways gnats enter a home, because commercial greenhouses almost always have some background gnat population.

Storing open bags of potting mix indoors can also invite trouble. Fungus gnats will lay eggs in an unsealed bag of moist peat mix sitting in a closet, and when you use that soil months later, you introduce a ready-made population into your pot. Seal unused potting mix tightly or store it in a sealed bin. Some growers microwave or bake small batches of potting mix before use to sterilize it, which is effective but smells terrible. A simpler option is to let the mix dry out completely in a sealed container before using it: eggs and young larvae die without moisture.

Keeping a predatory mite population alive in the soil is another long-term prevention strategy. If you introduce Stratiolaelaps scimitus once, the mites can persist in the pot as long as they have something to eat. When gnat larvae appear, the mites’ population rises to match. When gnats disappear, the mites feed on other soil organisms and wait. It is a self-regulating system that works quietly in the background.

When Gnats Signal a Bigger Problem

Sometimes fungus gnats are a symptom rather than the disease. A money tree sitting in chronically soggy soil is at risk of root rot whether or not gnats are present. If the trunk feels soft or mushy at the base, if the roots are black and slimy when you unpot the plant, or if the leaves yellow and drop despite correct light and feeding, root rot may already be underway. Pythium splendens has been confirmed as a cause of stem rot in Pachira aquatica specifically.⁸ Because fungus gnat larvae can vector Pythium through the soil, a gnat infestation in a money tree with compromised roots could make the rot worse or spread it to healthy tissue.⁹

In that scenario, treating the gnats is necessary but not sufficient. You also need to address the rot: trim away affected roots and stem tissue with sterile tools, let the cuts dry briefly, repot in fresh fast-draining mix, and hold off on watering for several days. Addressing both the pathogen and the pest at the same time gives the plant the best chance at recovery.