Gnats are small flying insects that are often considered pests. They are attracted to the smell of decaying organic matter and moist environments. Many houseplants and outdoor garden plants attract gnats due to the optimal conditions they create for gnat reproduction and development. Understanding why plants attract gnats can help gardeners and indoor plant owners prevent and control gnat infestations.
What Are Gnats?
Gnats are small flies that belong to several families, including fungus gnats, gall gnats, and phorid gnats. The most common gnats found around plants are fungus gnats, which belong to the families Mycetophilidae and Sciaridae.
Fungus gnat adults are about 1/8 inch long and have long, thin legs and antennae. They are weak fliers and commonly hover around plants and organic debris. The larvae are thin, white or transparent, and up to 1/4 inch long. They live in soil, compost, or other decaying plant material, where they feed on fungi, algae, and plant roots.
Why Are Gnats Attracted to Plants?
There are a few key reasons why gnats are attracted to indoor and outdoor plants:
Moist soil
Gnats need moist environments to survive and reproduce. Female fungus gnats lay eggs in soil, compost, or other decaying organic substrates that have high moisture levels. The larvae thrive in wet conditions. Dry soil discourages gnats.
Decaying organic matter
Like fruit flies, gnats feed on fungi, algae, bacteria, and decaying plant material. Wet potting soil, rotting leaves, crowded plant roots, and compost heaps provide an abundant food source for gnats.
Nitrogen-rich fertilizers
Gnats are attracted to the ammonia smell and nitrogen content of fertilizers and organic matter. Use of animal manure, blood meal, or excessive synthetic fertilizers can lead to gnat problems.
Poor drainage
Excess moisture caused by poor drainage or overwatering encourages gnat reproduction. Larvae and eggs need wet substrates. Improving drainage and only watering when soil is partly dry helps control gnats.
Damaged roots
Gnats are attracted to the sugars and nutrients released by damaged plant roots or decaying root debris. Repotting or transplanting shock can initially attract more gnats to vulnerable plants.
Signs That Gnats Are Present
There are a few common signs that indicate the presence of gnats around houseplants or in gardens:
– Adults flying around soil and plants when disturbed.
– Larvae visible in potting mix or top layers of soil.
– Roots appearing damaged or rotten.
– Fungus on the soil surface.
– Small black flies swarming around plant containers or garden beds.
– Plants declining for no apparent reason.
If these signs are noticed, inspect soil closely for bugs. Sticky traps can also be used to monitor for flying adults.
Houseplants That Attract Gnats
While any houseplant can get gnats if overwatered, some types are more prone to infestations than others. Common houseplants that attract gnats include:
Potted herbs
Basil, parsley, mint, chives, and other herbs are very susceptible to fungus gnats. Their moist soil, organic matter, and nitrogen inputs attract pests.
Tropical foliage plants
Philodendrons, pothos, Chinese evergreens, and prayer plants from the tropics like abundant moisture and rich soil – perfect for gnats.
Orchids
Beautiful but delicate orchids are notorious for developing fungus gnat problems in damp potting mixes. Their spongy aerial roots also provide habitat.
African violets
With fuzzy leaves and moisture-loving roots, African violets are magnets for flying pests like gnats. Overwatering encourages infestations.
Potted flowering plants
Gnats enjoy the moist soil needed for beautiful blooms in plants like cyclamen, azaleas, chrysanthemums, begonias, and impatiens.
Outdoor Plants That Attract Gnats
Gnats plague certain species growing in outside gardens and landscapes. Some of the outdoor plants most prone to gnats include:
Decaying leaf litter
Piles of rotting leaves are breeding grounds for fungus gnats. Leaf litter under trees attracts legions of larvae.
Vegetable gardens
Nitrogen inputs and moist soil create an appealing habitat for gnats on vegetable plants like tomatoes, cabbage, lettuce, and carrots.
Potted nursery plants
Gnats easily infest the wet soil of containerized perennials, trees, shrubs, and bedding plants before transplanting.
Compost piles
Active compost teems with microscopic life, making it a hotspot for fungus gnats. Turning and aerating compost can help deter them.
Lawns and turf
Overwatering and nitrogen fertilization of lawns encourages larvae development. Dryer grass areas have fewer issues.
Planter boxes
The contained soil in planter boxes of flowers and herbs stays moist, attracting breeding gnats.
Life Cycle of Gnats
Gnats develop through four stages – egg, larva, pupa, and adult. Understanding their life cycle helps control them.
Eggs
– Female gnats lay up to 200 eggs in top layers of damp soil or potting mix.
– Eggs hatch within 4 to 6 days into larvae.
Larvae
– Legless white larvae feed on organic matter for 10 to 14 days.
– Larvae molt 4 times, reaching up to 1/4 inch long.
Pupae
– Larvae form cocoons and enter dormant pupal stage for 4 to 8 days.
– Adults emerge from pupae and fly to plants to restart cycle.
Adults
– Adult gnats live for about 10 days.
– Females lay eggs within a few days of emerging.
– Adults feed on nectar, fungi, and plant exudates.
Effects of Gnats on Plants
High numbers of gnats can damage plant health in several ways:
Stunted growth
Larvae feeding on plant roots reduces water and nutrient uptake. Plants fail to thrive.
Wilting or dying
Extensive larval feeding can destroy roots, causing foliage to wilt and die.
Spreading disease
Gnats may transmit fungal diseases like root rot, damping off, or botrytis.
Cosmetic damage
Tunneling larvae leave unsightly trails on roots and tubers.
Delayed flowering/fruiting
Root damage interferes with nutrients needed for buds and fruit.
While a few gnats are usually harmless, large infestations can quickly affect plant health and aesthetics.
How to Prevent Gnats in Potted Plants
Keeping houseplants and potted plants gnat-free involves using cultural and physical controls:
Allow soil to dry between waterings
Moisture-loving gnats need wet soil. Let soil partially dry out before watering again.
Remove excess debris
Eliminate rotting leaves or old potting mix that breed pests.
Use sterile potting mixes
Sterilized, soilless mixes contain no gnat eggs or larvae.
Apply sand/gravel mulch
A coarse top dressing dries out soil and deters egg-laying adults.
Repot frequently
Old potting soil in crowded pots retains moisture and attracts gnats.
Discard damaged roots/tubers
Inspect bulbs and tubers for larval tunnels and discard damaged ones. Prevent pests from spreading.
Avoid overcrowding
Dense roots compete for space and air, creating a moist habitat loved by gnats.
How to Prevent Gnats in Gardens
Preventing outdoor gnat issues involves cultural controls and sanitation:
Promote soil drying
Allow garden soil to dry between waterings. Improve drainage if needed.
Eliminate leaf litter + debris
Rake up fallen leaves, mulch, and dead plants where larvae breed.
Aerate lawns
Core aeration improves drying and disrupts larvae in compaction-prone turf.
Turn compost regularly
Frequently turning compost piles exposes larvae to heat, drying them out.
Water early in the day
Soil dries fastest when watered early. Evaporation deters gnats.
Use drip irrigation
Targeted drip irrigation wets only soil, not leaves. Dry leaves deter adults.
Allow mulch to dry
Thick, moist mulches encourage larvae. Allow mulch to dry between waterings.
Solarize soil
Heating soil by covering moist beds with plastic kills eggs and larvae.
How to Get Rid of Gnats
If gnat populations are already high, use these organic and chemical controls:
Sticky traps
Yellow or blue sticky traps lure and catch flying adults. Prevent reinfestation by catching emerging gnats.
Sand barriers
An inch of sand or diatomaceous earth on soil dries out the top layer and prevents egg-laying.
Larvicides
Use bacillus thuringiensis israelensis (BTI) or insecticidal nematodes to kill larvae in soil and compost.
Botanical insecticides
Plant-derived products with neem, pyrethrins, or spinosad quickly kill larvae and flying adults on contact.
Remove/replace infested soil
Discarding badly infested potting mix or garden soil removes larvae. Replace with fresh, sterile soil.
Natural predators
Predatory soil mites and nematodes feed on gnat larvae and eggs. Buy them from garden suppliers or encourage native species.
Alter watering practices
Allow soil to dry out more between waterings. Fix sources of excessive moisture fueling gnats.
Conclusion
Gnats frequently infest indoor plants and gardens due to the damp, organic matter-rich environment. While a nuisance, these fragile insects are easily controlled through cultural practices that promote dryness. Sticky traps, insecticides, and natural predators can treat high populations. With a little diligence, it is possible to control gnats and enjoy pest-free plants.
