Gnats. Just the word can make any homeowner cringe. These tiny, annoying flies seem to appear out of nowhere and quickly become a nuisance, buzzing around your face, hovering near your food, and generally making your home feel less than peaceful. If you’re tired of swatting away these uninvited guests, you’re in the right place. This guide will provide you with a definitive, two-step method to effectively get rid of gnats in your house and keep them from coming back.
how to kill fungus gnats in indoor house plants
Are Those Gnats Really Harmful? Understanding the Pest
Before diving into solutions, it’s important to understand what you’re dealing with. The gnats you’re seeing in your house are most likely fungus gnats. These small, dark, mosquito-like insects are particularly attracted to moist environments and decaying organic matter. While they are often found buzzing around houseplants, they can also be drawn to overripe fruits, garbage disposals, and damp areas in your kitchen and bathrooms.
The good news is that adult fungus gnats are mostly harmless to humans and pets. They don’t bite or transmit diseases. However, their presence is incredibly irritating. They are drawn to carbon dioxide, meaning they will often fly around your face, making their presence constantly known. Furthermore, they can contaminate food and drinks, and their sheer numbers can be overwhelming.
The real issue with fungus gnats lies in their larvae. These tiny, translucent larvae live in the top layer of soil, feeding on fungi and decaying plant matter. In large infestations, particularly when their food source dwindles, they may start to feed on plant roots. This root damage can be detrimental, especially to seedlings, young plants, and delicate cuttings, potentially stunting their growth or even killing them.
Identifying Fungus Gnats: The Potato Test
If you’re not entirely sure if you’re dealing with fungus gnats, or if you want to pinpoint which of your houseplants might be the source of the infestation, the potato test is a simple and effective method.
Fungus gnats are often mistaken for fruit flies, but there are key differences. Fungus gnats are smaller, more slender, and have longer legs, resembling tiny mosquitoes rather than the rounder, tubby fruit fly. They are also silent, unlike mosquitoes. However, if you’re still unsure, the potato test can confirm your suspicions.
Here’s how to perform the potato test:
- Slice a raw potato: Cut a raw potato into several thin slices, about ¼ inch thick.
- Place potato slices on the soil: Lay the potato slices directly on the surface of the soil of any plants you suspect are infested.
- Wait and check: Leave the potato slices for a few hours, ideally overnight.
- Inspect for larvae: Carefully lift the potato slices and check the underside. If you have fungus gnats, you’ll likely find small, white, translucent larvae feeding on the potato.
If you find larvae, it’s time to take action and implement a treatment plan to get rid of these pests.
The Two-Step Solution: Eradicating Gnats Effectively
The most effective way to eliminate gnats in your house is to address both the adult gnats and the larvae simultaneously. This two-pronged approach breaks the gnat life cycle, ensuring complete eradication. This method uses readily available and safe products: sticky traps to target adult gnats and Mosquito Bits (containing BTI) to eliminate larvae.
Step 1: Trapping Adult Gnats with Sticky Traps
Sticky traps are a non-toxic and highly effective way to capture adult fungus gnats. These traps use bright colors, often yellow or green, to attract gnats, and are coated with a sticky adhesive that traps the insects when they land.
Choosing and Using Sticky Traps:
- Types of Sticky Traps: You can find sticky traps in various forms, including hanging strips, stakes that insert into soil, and flat cards. For indoor plants and general house gnat control, stake or flat card traps are ideal. Green sticky traps are often reported to be more effective and discreet for indoor plant use compared to traditional yellow traps.
- Placement for Maximum Impact:
- For indoor plants: Place sticky traps directly on the soil surface or insert stake traps into the soil of your potted plants. Adult gnats often congregate near the soil surface where they emerge.
- General house gnat control: Place flat traps near areas where you see gnats congregating, such as kitchen counters, near fruit bowls, or in bathrooms.
- Tips for Yellow Sticky Traps: If using traditional yellow sticky traps, consider these tips to enhance their effectiveness:
- Expose only one side: Peel off the protective paper from only one side of the trap.
- Lay flat on soil: For potted plants, lay the yellow trap flat on the soil surface, sticky side up. This maximizes the trapping area and is very effective.
- Cut traps for better use: Yellow traps can be cut into smaller pieces to fit smaller pots or to distribute traps more widely. Cut them before peeling off the paper to avoid sticky scissors.
- Double the lifespan: After a couple of weeks, or when the trap is covered in gnats, flip it over and peel off the paper from the other side for a fresh sticky surface, effectively doubling the trap’s use.
- Green Sticky Traps Advantages: Green traps designed for indoor plants often come pre-mounted on stakes and are waterproof, potentially lasting longer and maintaining stickiness even with watering.
Step 2: Eliminating Larvae with “Mosquito Tea” (BTI)
While sticky traps effectively reduce the adult gnat population, they don’t address the root of the problem – the larvae living in the soil. To eliminate the larvae, we need to use a biological control agent called BTI (Bacillus thuringiensis israelensis). BTI is a naturally occurring bacterium that is toxic to mosquito and fungus gnat larvae but harmless to plants, humans, pets, and beneficial insects.
Mosquito Bits (or Mozzie Bits as they are known in some regions) are a readily available product containing BTI. We will use Mosquito Bits to make “Mosquito Tea,” a solution that you will use to water your plants, effectively targeting and killing the larvae in the soil.
Making and Using “Mosquito Tea”:
- Gather your supplies: You will need Mosquito Bits (or Mozzie Bits), warm water (not boiling), and a container to soak the bits in. A mesh bag or cheesecloth can be helpful for easy removal of the bits later.
- Prepare the “Mosquito Tea” mixture:
- Ratio: Use 4 tablespoons of Mosquito Bits per 4.5 liters (approximately 1 gallon) of warm water. You can adjust this ratio for smaller or larger batches, maintaining the proportions.
- Soak the Mosquito Bits: Place the Mosquito Bits in the warm water. Warmer water helps the BTI infuse into the water more quickly. For warm water, soak for at least 30 minutes. For cooler water, you can soak for a couple of hours, or even overnight. Avoid using boiling water as it may harm the BTI. Using a mesh bag to contain the bits makes for easier cleanup later.
- Strain or remove the bits: After soaking, strain the mixture to remove the Mosquito Bits granules. If you used a mesh bag, simply remove the bag. The water now contains the BTI and is your “Mosquito Tea.”
- Water your plants with “Mosquito Tea”: Once the “Mosquito Tea” has cooled to room temperature, use it to water your plants thoroughly, just as you normally would. Ensure the “Mosquito Tea” saturates the top layer of the soil where the larvae reside.
- Watering method:
- Top watering: Top watering is generally more effective for fungus gnats as larvae are concentrated in the topsoil.
- Bottom watering (with a top-up): If you prefer bottom watering, allow the plant to soak until the topsoil is moist. You can also reserve a little “Mosquito Tea” to water the top surface to ensure the topsoil is treated.
- Frequency of treatment: Water your plants with “Mosquito Tea” every time you water, or at least every two weeks, until the gnat infestation is gone. Consistency is key to breaking the gnat lifecycle.
Using Mozzie Dunks (Alternative to Mosquito Bits):
If you can’t find Mosquito Bits, Mozzie Dunks are another product containing BTI that can be used, although the preparation is slightly different. Dunks are designed for larger bodies of water and release BTI slowly.
- Preparation for Mozzie Dunks: Break one Mozzie Dunk into quarters. Soak one quarter of a dunk in 4 liters of water overnight (approximately 12 hours). Warm water can help it dissolve better.
- Usage: Remove the undissolved dunk pieces (they can be reused). Use the infused water to water your plants as described above.
How BTI Works: Nature’s Gnat Control
BTI is a remarkable natural solution for pest control. It works by targeting the larval stage of fungus gnats. When larvae ingest BTI, it releases toxins that specifically disrupt their digestive system, leading to their death. Importantly, BTI is highly selective and only affects mosquito and fungus gnat larvae. It is completely safe for:
- Plants: BTI will not harm your houseplants.
- Beneficial insects: Bees, butterflies, and other beneficial insects are not affected.
- Humans and pets: BTI is non-toxic to humans, pets, birds, fish, livestock, and wildlife.
- Environment: BTI is biodegradable and environmentally friendly.
This makes “Mosquito Tea” a safe and responsible way to get rid of gnats in your house without resorting to harsh chemical pesticides.
Combining “Mosquito Tea” with Fertilizing
You can easily combine your gnat treatment with your regular plant care routine. “Mosquito Tea” can be mixed with liquid fertilizers. Simply prepare your “Mosquito Tea,” let it cool, and then add your liquid fertilizer as usual before watering. If using granular or powder fertilizers, ensure everything is well mixed in the water before applying.
How Long Does Gnat Treatment Take?
Patience is key when dealing with gnat infestations. While this two-step method is highly effective, it takes time to break the gnat lifecycle completely. Fungus gnats can complete their lifecycle from egg to adult in as little as 17 days in ideal conditions, but typically around 3 weeks in summer, and longer in cooler months.
Recommended Treatment Duration:
- Minimum: Treat for at least 4 weeks, even if the infestation seems minor.
- Ideal: Treat for 2 months (8 weeks) to ensure you have eliminated all life stages and prevent re-infestation.
Even if you notice a significant reduction in gnats quickly, continue the full treatment period to ensure complete eradication. Stopping treatment prematurely can lead to a resurgence of gnats as remaining larvae mature.
Preventing Gnat Re-infestation: Long-Term Strategies
Once you’ve successfully gotten rid of gnats in your house, preventing their return is crucial. Here are key preventative measures:
- Gnat Barrier: After treatment, consider applying a gnat barrier to the soil surface of susceptible plants, especially those that prefer consistently moist soil like Peace Lilies. Gnat barrier products, often made from pumice granules, create a physical barrier that prevents adult gnats from laying eggs in the soil. Avoid using diatomaceous earth (DE), as it is less effective when wet and can pose respiratory risks.
- Isolate New Plants: New plants are a common source of gnat infestations. Always quarantine new plants for at least 2-4 weeks before introducing them to your existing plant collection. This allows time to observe for any pests and treat them in isolation if necessary.
- Proper Soil Storage: Store potting soil in airtight containers, especially if kept outdoors. Moist soil stored outside is highly attractive to fungus gnats. If you are unsure about the storage of new soil, consider pre-treating it with “Mosquito Tea” or hydrogen peroxide before potting.
- Avoid Overwatering: Fungus gnats thrive in moist soil. Allow the topsoil of your houseplants to dry out slightly between waterings. This makes the environment less appealing to gnats.
- Don’t Leave Watered Plants Outdoors: Avoid placing freshly watered plants outdoors, as this makes them highly susceptible to gnat infestations from the outside environment. If you do put plants outside, ensure the soil surface is relatively dry first.
Where Do Gnats Come From? Understanding the Source
Understanding where gnats come from helps in prevention. The most common sources are:
- New Plants: As mentioned, new plants often harbor gnat eggs or larvae in their soil.
- Outdoor Soil: Soil stored outdoors can easily become infested with gnats.
- Bringing Plants Indoors After Being Outside: Plants left outside, especially after watering, can attract gnats that then hitch a ride back indoors.
By being mindful of these sources and implementing preventative measures, you can significantly reduce the risk of future gnat infestations.
Enjoy a Gnat-Free Home
Dealing with gnats can be frustrating, but with the right approach, you can effectively eliminate them and maintain a pest-free home. This two-step method using sticky traps and “Mosquito Tea” is a proven solution that is both safe and highly effective. Remember to be patient, consistent with your treatment, and proactive with prevention. Say goodbye to those annoying buzzing gnats and enjoy your peaceful, plant-filled home once again!
