Soil gnats, also known as fungus gnats, are just about as Houseplants 101 as it gets. They’re easy to get, easy to get rid of, and easy to prevent in the future. Most plant parents will experience this pesky pest at least once in their plant journey - they can even be thought of as something that’s unsurprising for beginners, like falling down when learning to ride a bike or forgetting to wet your canvas when you’re learning how to paint.
As with many pests, it’s not necessarily worth your time to try and figure out wherethe soil gnats that may be affecting your houseplants came from. Soil gnats are basically everywhere, and soil gnat eggs can lay dormant in the soil for a good while and only hatch when conditions allow, so it’s usually impossible to try to figure out when the plant was exposed to soil gnats.
Soil gnats usually start appearing when the soil of your plant has been holding on to water for too long. This can be caused by overwatering (whether by too much volume or by watering too frequently), pots without drainage holes, plants that are potting in much too large of a pot, or soil that is compressed and/or does not dry out easily. If you notice soil gnats, take it as an indication that your houseplant has experienced overwatering in some form and take steps to dry out the soil. Any yellowing, browning, or wilting is likely a result of this watering problem and not directly caused by the soil gnats.
To treat soil gnats:
- Soil gnats need wet conditions to hatch and reproduce. Ensure your soil is dry before treatment.
- Water through the soil with a 1:1 mix of water and hydrogen peroxide. The hydrogen peroxide will kill gnats and eggs without hurting the roots of the vast majority of houseplants.
- It may take several applications to kill off all of the gnats. Each application should lessen the population significantly.
Once the gnats have all been killed off, take steps to ensure that the houseplant does not experience the same overwatering issue that caused the gnats. Check to make sure that your pots have drainage holes, fluff the soil to make sure that it’s aerated and draining properly, and don’t water until the soil has dried sufficiently between waterings (the level of dryness to wait for varies depending on the plant).
You can also spray down the plant and the top of the soil occasionally with neem oil, which acts as a sort of quarantine for your plants - most pests hate neem oil and will avoid landing on it, which goes a long way towards keeping soil gnats off of your soil. As an added bonus, neem oil is an all-natural oil extracted from neem seeds that works beautifully as a leaf polish.
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