Gnats are small, flying insects that can quickly turn a pleasant patio into an irritating environment. These pests are attracted to moisture and decaying organic matter, which are common elements in outdoor living spaces. Effectively eliminating them requires a two-pronged approach: quickly reducing the adult population and destroying the breeding sites. This guide provides practical steps to reclaim your patio by addressing the specific sources that allow these nuisances to thrive.
Pinpointing the Gnat Source on Your Patio
The first step in control is identifying the specific type of gnat, as their breeding habits dictate the treatment method. The two most common culprits on a patio are fungus gnats and drain flies, both of which seek out damp, nutrient-rich environments. Fungus gnats are slender, dark-colored flies drawn to the moist potting mix of container plants. They lay eggs in the top inch or two of soil, where the larvae feed on fungi and decaying plant material.
Drain flies, also known as moth flies, have a fuzzy, moth-like appearance and are attracted to stagnant water and the gelatinous biofilm that accumulates in drains. On a patio, check floor drains, clogged gutters, bird baths, or any area where water stands for more than a day. If the gnats hover around potted plants, you are likely dealing with fungus gnats. If they emerge from a drain when disturbed, the problem is drain flies. Understanding the source allows for a targeted elimination strategy.
Quick-Action DIY Traps and Repellents
While eliminating the source is the long-term solution, immediate relief from adult gnats can be achieved using simple, non-toxic traps. The most effective method is the apple cider vinegar and dish soap trap, which exploits the gnat’s attraction to fermented scents. To create this trap, mix a few tablespoons of apple cider vinegar with a few drops of liquid dish soap in a small, shallow bowl.
The vinegar acts as a powerful lure, drawing the gnats in with its fruity aroma. The dish soap breaks the surface tension of the liquid, preventing the insects from landing and flying away. Once the gnats attempt to drink the mixture, they fall in and drown. A similar trap can be made using stale wine or beer, as fermentation also produces attractive odors.
Another immediate measure is to use a small oscillating fan positioned near your seating area. Gnats are weak fliers and struggle to navigate in a gentle breeze, making it difficult for them to land or hover. The increased air circulation also helps to dry out the surface of nearby soil or damp areas, which discourages adults from laying eggs. These strategies provide quick population reduction while you implement permanent solutions.
Eliminating Larvae in Soil and Drains
Targeting the larvae is the only way to break the gnat life cycle and achieve lasting control, as adult gnats only live for about a week. For fungus gnats breeding in potted plants, allow the top layer of soil to dry out completely between waterings. Since the larvae live in the top two inches of moist soil, depriving them of this moisture is an effective control measure.
For a more aggressive treatment, apply a biological control agent containing Bacillus thuringiensis israelensis (BTI) to the soil. BTI is a naturally occurring bacterium that is harmless to humans, pets, and plants. When ingested by the gnat larvae, it releases proteins that disrupt their digestive system, causing them to die. This product is typically mixed with water and applied as a soil drench, ensuring the solution reaches the larvae’s feeding zone.
If the source is a patio drain, the larvae are feeding on the organic sludge, or biofilm, lining the pipes. Chemical drain cleaners are generally ineffective and can damage plumbing. The preferred method is a biological or enzyme-based drain cleaner. These products contain beneficial microbes that actively digest the organic matter, eliminating the larvae’s food source and breeding ground. For best results, physically scrub the inside of the drain opening with a stiff brush before applying the enzyme cleaner to dislodge the thickest buildup.
Long-Term Environmental Prevention
Sustained gnat control relies on making the patio environment permanently inhospitable to these moisture-loving pests. Adjusting your watering routine for potted plants is an effective preventative measure against fungus gnats. Instead of frequent, shallow watering, water deeply but less often, allowing the soil to dry out several inches down before re-watering.
Improving drainage is equally important. Ensure that all patio floor drains are clear of debris and that water does not pool in plant saucers or low-lying areas. Removing organic debris, such as fallen leaves, old fruit, or spilled food, eliminates potential secondary breeding sites. These materials decompose quickly and provide the moist, nutrient-rich environment that gnats seek for laying eggs.
Finally, consider applying a top dressing of sand, gravel, or decorative pebbles to the surface of potted plant soil. This layer creates a dry barrier that prevents adult fungus gnats from accessing the moist soil beneath to lay eggs. By consistently managing moisture and removing organic matter, you can maintain a patio environment that naturally deters gnats.