Fungus gnats in houseplants: how to get rid of them

Adult fungus gnats are small, dark, delicate flies with long legs and antennae. They often stay near pots or appear at windows. Their larvae are translucent, wormlike and have a dark head. Appearance and location are clues, rather than a certain identification from a distant speck. Colorado State University Extension: fungus gnats

Check the likely source before treating every plant:

These are starting points, not a diagnostic key. Different small flies breed in different materials; finding flies beside a plant does not establish that the plant is the source. Colorado State University Extension: flies in the home

If you cannot make out the insect, try a clear close-up and ask a local extension service for identification before choosing a treatment.

Webbing on leaves? Check for spider mites.

The adults do not damage plants. Larvae mostly feed on fungi and organic matter, but can also damage roots, particularly at high numbers and on seedlings or young plants. A wilting plant may instead have a watering, drainage or root problem; flies alone do not establish the cause. UC Statewide IPM: damage

If leaves are also changing color, use our yellow-leaf checklist to gather wider context rather than assigning every symptom to the gnats.

1. Check moisture and drainage

Let the mix dry appropriately between waterings. Check below the surface and compare it with the needs of that plant. Potting mix, humidity and temperature affect watering; one fixed interval does not fit every pot. Do not turn pest control into prolonged drought for a plant that needs more consistent moisture. University of Maryland Extension: watering

Empty water collected in saucers or outer pots. Check that drainage is working. Iowa State recommends allowing the surface to dry and keeping plants out of standing water. Iowa State University Extension: fungus gnats

Our guide to checking when a houseplant needs water explains how to build that decision into your routine.

2. Remove breeding opportunities

Clear decaying plant debris and avoid keeping potting mix continually wet. Check other damp material nearby, too. UC IPM recommends managing moisture and organic debris, and storing clean potting mix in closed containers. UC Statewide IPM: water and soil management

For your own checks, label pots by location: “desk,” “kitchen” and “bedroom,” for example. Note where flies repeatedly appear instead of assuming the whole collection has the same problem.

3. Use sticky cards to watch adults

Yellow sticky cards can help you see adult activity. They cannot stop insects already developing in the mix from emerging. A card with flies on it shows that it is catching adults, not that the breeding problem is solved. Iowa State University Extension

For a useful comparison, write the date on a new card and record what you see over a consistent interval. Compare new catches rather than the total on an old card. This is a practical observation method, not a measured treatment trial.

4. If the problem persists, consider the larvae

For continuing infestations, UC IPM describes biological options including Bacillus thuringiensis subsp. israelensis (Bti) and Steinernema feltiae nematodes. Bti for fly larvae differs from Bt products for caterpillars. Choose a product labeled for the pest and intended indoor-plant use where you live, and follow its current instructions. Do not substitute a homemade dose or an old online application schedule. UC Statewide IPM: biological control

The University of Illinois recommends observation and integrated pest management rather than relying on a single tactic. Ask your local extension service about a persistent infestation, especially if identification is uncertain or the plant is declining. University of Illinois Extension

Fungus gnats have eggs, larvae, pupae and adults, so removing the visible adults leaves other stages behind. Colorado State describes a life cycle of about three to four weeks at typical room temperatures of 65–75°F. Timing varies with conditions; this is not a guaranteed clearance date. Colorado State University Extension: life history

Use a short record to decide what to check next. For example:

Desk plant: flies near the pot on Monday; mix still damp below the surface; water found in the outer pot and emptied. New sticky card dated Monday. At the next check, compare moisture, new catches and the plant's condition.

The example is a note template, not a report from a tested plant. Keep treatment details and dates if you use a labeled product. If the pattern does not improve, revisit the source: Iowa State notes that fungus gnats can also originate in other wet areas, including condensation trays and unused drains. Iowa State University Extension

Prepared by the Bloom team with AI assistance, using the extension guidance linked throughout. Sources checked October 29, 2026. The observation examples are editorial suggestions, not first-hand treatment tests. No horticulturist has reviewed this article, and the cited institutions have not reviewed or endorsed Bloom. Product descriptions were checked against Bloom's public iPhone listing and current site/app source.

• Fungus Gnats — UC Statewide IPM
• Fungus Gnats as Houseplant and Indoor Pests — Colorado State University Extension
• Flies in the Home — Colorado State University Extension
• Diagnosing Houseplant Problems Caused by Insect Pests — Iowa State University Extension
• Houseplant pests and how to manage them — University of Illinois Extension
• Watering Indoor Plants — University of Maryland Extension