Gardening is a productive, enjoyable hobby, especially when you see your plants’ colorful blooms and lively foliage. However, such beauty requires a considerable amount of effort and attention. Sometimes, pests and harmful microorganisms like gnats can get in the way of your pleasant gardening experience.
Gnats are bad for plants because their larvae feed on roots and consume essential nutrients in the soil that should otherwise be used for plant consumption. They can also transmit fungal infections, and large enough populations of gnat larvae can stunt the growth of your plants.
In this article, you’ll learn how gnats can affect plants and how to control or eliminate them to prevent further damage to your garden. I’ll also discuss how to avoid a gnat infestation from occurring in the first place. So, read on if you want to learn more about keeping your garden gnat-free.
How Gnats Affect Plants
Seeing adult gnats hovering around your indoor plants may seem annoying at first, but they don’t actually pose any real danger to your plants. They are simply attracted to the moisture in the soil, especially if it’s rich in organic matter.
These conditions make the soil a suitable substrate for adult female gnats to lay their eggs. They are prolific breeders as they can produce approximately 150 eggs during their one-week life span.
As the eggs hatch, the larvae will need nutrients to grow. That’s when they start wreaking havoc in your indoor garden. Below are some ways gnats can affect your plants negatively:
Gnat Larvae Consume Essential Nutrients in the Soil
Each gnat’s life span is approximately 25 days. Adult female gnats live for 5-7 days and can produce at least a hundred eggs each. As gnat larvae hatch from the eggs, they feed on organic matter in the soil.
While this doesn’t seem like a serious issue considering the small size of gnat larvae (⅛ inch / 2.5 mm), their large population can be troublesome. Moreover, gnats stay in larvae form for roughly ten days, inflicting damage during such a period.
Eventually, these larvae will grow into adults and lay several hundreds of eggs in the soil. A large population of gnat larvae can consume considerable amounts of nutrients.
It can be especially troublesome for potted plants because of the small soil volume and the limited space. The pot can be overwhelmed with gnat larvae before you know it. As a result, the essential nutrients in the soil will quickly become depleted, depriving plants of their nutritional needs.
The larvae also feed on decaying plant matter that would otherwise produce nitrogen for the plant as they decompose. As the nitrogen levels in the soil decrease, the plant will start growing yellowish or pale green leaves. This can also result in stunted growth.
Gnat Larvae Feed on Plant Roots
As the organic matter in the soil runs out or if the gnat larvae cannot access the nutrients deep in the soil, they may start feeding on plant roots. Hundreds to thousands of larvae munching on the roots can cause significant damage.
Young plants are more susceptible to such damage and may start wilting. So if you notice your plants wilting despite providing them with sufficient basic needs, such as light, water, and ideal temperature, you might as well check the soil for the presence of the characteristic white gnat larvae with black tips.
They are tiny but relatively easy to spot, and it will be hard to miss them if there are hundreds of them lurking in your soil. Seeing adult gnats flying around your plant is another indicator that there are gnat larvae in your pot.
Gnats Can Transmit Fungal Disease to Plants
Gnats are sometimes referred to as fungus gnats because their larvae feed on fungi in the soil. These gnats usually include Pythiums and Fusariums. These fungi are responsible for root rot and other health issues in plants.
Root rot sometimes occurs in plants as a secondary infection following gnat larvae infestation. Gnats thrive in consistently moist soil, and water-logged conditions can weaken the plants’ defenses against diseases.
There are several ways gnats can transmit fungal diseases to plants. Let’s take a deeper look at them below:
Through Cuts and Wounds on the Plant
As larvae feed on plant roots, they expose the plant to harmful microbes in the soil through the wounds they create. These microbes can then invade the plant tissue and cause severe damage to the plant.
Moreover, since the plants most likely have weakened defenses due to excess moisture and physical damage from the gnat larvae, they won’t be able to fight off the fungal diseases. You will then notice several symptoms typical of root rot, such as wilting and yellowing leaves.
Through Their Digestive Tract
As the larvae mature and turn into adult gnats, they can fly to nearby pots and excrete wastes containing fungi in the soil. As a result, the fungi spread from one pot to another.
This situation can be troublesome if you have numerous potted plants in your house. The same problem occurs in many nurseries and greenhouses where the plants are in an enclosed space, making disease transmission through flies pretty common.
How To Get Rid of Gnats
Once you confirm that gnat infestation is responsible for your gardening troubles, the best course of action is to control their population. It’s important to note that it may be impossible to eliminate them entirely unless you replace your soil.
Getting rid of them can also be challenging while ensuring that you’re not causing more damage to your plants. I discourage using pesticides or insecticides because the harmful chemicals may present more problems to your plants. Moreover, not all pesticides are effective against all life stages of gnats.
Instead, you can use manual, biological, and chemical interventions to control the gnat population in your garden without harming your plants. Let’s check out the details below:
Use Sticky Traps To Catch Adult Gnats
When you find adult gnats flying around your potted plants, you can catch them using sticky traps. You can hang the sticky trap on your plant’s branch or stick it into the soil.
The downside of this method is that while it can catch many adult gnats, it cannot eliminate the eggs that have already been laid. Moreover, it can be unsightly with all the dead gnats sticking to the paper.
Nonetheless, if you are interested in this method, you may want to try Stingmon Store’s Sticky Traps (available on Amazon.com). The product has a cute butterfly or flower design to help distract your attention from the gnats. It is equipped with a strong, long-lasting adhesive to ensure that insects remain trapped.
Use Apple Cider Vinegar to Lure the Gnats
Adult gnats are attracted to the smell of apple cider vinegar. Placing a shallow bowl with 50 ml (1.7 fl. oz.) of apple cider vinegar close to your pots will lure the gnats away from your plants. They will most likely fly toward the liquid and drown in it.
You can also add a few drops of liquid dish detergent to the vinegar to make the liquid stickier and trap the gnats more effectively.
Here is a video showing how apple cider vinegar works against gnats:
Introduce Gnat Parasites or Predators to Your Garden
Although the idea seems unpleasant, introducing natural gnat parasites and predators to control the gnat population is a widely used practice by greenhouse and agricultural farmers.
These critters do not pose any harm to plants or humans but are effective against gnats. However, sufficient knowledge about properly handling these organisms is necessary for optimal results. Here’s how they work:
- Parasites. Parasitic nematodes or roundworms can invade the guts of gnat larvae and kill them off by releasing toxic substances into their system.
- Predators. Rove beetles and Hypoaspis mites are beneficial to the garden as they feed not only on gnat larvae but also on thrips pupae or root aphids. They actively seek out gnat larvae and control the population.
It is relatively easy to find suppliers of these organisms. However, home gardeners may feel reluctant to use them due to the challenging handling requirements. If you’re interested in trying out this approach, it is best to consult an experienced gardener or the supplier on how to store and use them properly.
How To Prevent Gnat Re-Infestation
Since the steps mentioned above are not definitive ways to eliminate gnats, you can try some other methods to prevent gnat re-infestation.
As soon as you notice adult gnats flying around your plants, you can assume that they have already laid eggs in the soil. It’s only a matter of time before they emerge as larvae and inflict harm to your plants.
Here are some things you can do to ensure gnats do not infest your soil again:
Repot Your Plants Using Sterile Soil
Considering how quickly fungus gnats multiply, you may be tempted to remove them immediately. You can prevent them from harming your plants again by repotting your plant using sterile soil.
You can follow the steps below:
- Pouring boiling water (212 °F / 100 °C) over your soil before use is often enough to kill fungus gnat larvae and other harmful microorganisms in the soil; however, you must saturate the soil with hot water and let it drain.
- Cover the pot or container with a clean piece of cloth while waiting for the soil to cool to prevent gnats from laying eggs on the moist soil.
- Carefully dig out your plant from the gnat-infested soil, but be careful with the roots as they may be damaged.
- Remove as much soil as possible from the roots, and place the plant under gentle running water to remove the remaining soil and wash away the remaining gnat larvae.
- Nip off damaged portions of the roots and remove dead foliage.
- Transplant your plant into the cool, moist, sterile soil in a new, clean pot.
Alternatively, you can purchase sterile potting mixes from reputable sellers to ensure there are no existing parasites, pests, or harmful microbes in your plants’ growing substrate.
You can also place sticky traps in your pot or place a shallow bowl of apple cider vinegar close to your plant to catch any persisting gnats.
Use Soil and Pots With Good Drainage
In addition to being sterile, your plant’s soil should also have good drainage to prevent too much moisture that attracts gnats. A breathable pot with holes at the bottom can also provide good aeration and drainage and protect your plant from water-logged conditions.
Avoid using plastic pots because they are not breathable. Instead, you can use unglazed clay pots because they are breathable and can absorb the excess moisture from the soil.
Avoid Over-Watering Your Plants
Adult gnats lay their eggs in moist soil, so depending on your plant’s water requirements, you may need to let the soil dry 1-2 inches (2.5 – 5 cm) from the top before adding more water. This is possible for drought-tolerant plants.
However, if your plants require consistently moist soil, you may need to use a wick-watering system. It can deliver just the right amount of water your plant needs without the risk of over-watering. It can also help conserve water in the long run.
Select Drought-Tolerant Plants
It is easier to manage drought-tolerant plants because they are more resistant to fungus gnats and other diseases caused by excess moisture. These plants can handle a bit of dryness between watering, making the soil condition inhospitable to moisture-loving pests and microbes, such as gnats, snails, and fungi.
Seeing gnats around your plants can be alarming. Thankfully, they’re usually manageable.
Adult gnats are not harmful to your plants. However, they can lay hundreds of eggs, and the resulting larvae can feed on the soil nutrients and your plants’ roots. This behavior of gnat larvae can eventually lead to plant death.
While it can be challenging to eliminate gnats from your garden, you can employ several approaches to control their population, such as trapping them in sticky paper or vinegar. You can also prevent their infestation by using sterile soil and avoiding over-watering your soil.