Fungus gnats are tiny insects commonly found in houseplants. While the adults are mostly a nuisance, the larvae live in the soil and can feed on plant roots, stressing plants over time. Fortunately, fungus gnats are usually easy to control once their life cycle is understood.
Quick Fungus Gnat Tips
- Adults are harmless but annoying
- Larvae live in moist potting mix
- Overwatering is the main cause
- Letting soil dry breaks the life cycle
- Most infestations are easy to control
How to Identify Fungus Gnats
Adult fungus gnats are very small, black insects often seen flying near houseplants or resting on the soil surface. They resemble tiny mosquitoes but do not bite.
The larvae live in the top 2–3 inches of moist potting mix, especially mixes high in peat moss. Under normal indoor conditions, their entire life cycle can be completed in about ten days.
Why Fungus Gnats Appear
Fungus gnats thrive in consistently moist soil. Overwatering, poor drainage, and old potting mix that has broken down create ideal conditions for egg-laying and larval development.
Non-Chemical Control Methods
The simplest and most effective control method is to allow the top 2 inches of potting mix to dry out between waterings. This disrupts the gnat life cycle and is beneficial for most houseplants.
Repotting plants into fresh, well-draining potting mix can also reduce infestations, especially if the existing mix has compacted or broken down over time.
Chemical Control Options
If fungus gnats persist after adjusting watering practices, chemical controls may be used:
- Products containing permethrin can be applied to the soil surface to kill emerging adults.
- Bonide Systemic Houseplant Insect Control can be used to control larvae feeding in the soil.
Several control options are available, and the best choice depends on plant type and infestation severity. Our staff can help recommend the most effective solution for your situation.
Please read and follow all label instructions when applying any insect control products.