How to get rid of gnats in my houseplants

Gnats in houseplants are annoying. Known as fungus gnats, they're actually small flies about 1/8-inch long that are drawn to moist potting soil and decaying plant material at the base of indoor plants. While they look similar to mosquitoes, they don't bite. 

Because gnats in houseplants typically result when the potting mix contains too much moisture, the best way to prevent gnats from taking over your home is to avoid over-watering in the first place. But what if the damage is already done and you're dealing with a swarm of pesky flies surrounding your plants? Here, we walk you through the best ways to get rid of gnats in your house plants.

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How to identify gnats in indoor plants

One way to tell if you're about to run into a gnat problem is to look for eggs. Fungus gnats lay eggs in the soil and these eggs become larvae, which feed on fungi in the soil of plants. The fungus gnat larvae are around 1/4-inch long with a shiny black head and an elongated, whitish to transparent body.

In addition to fungi, they also like organic matter and will sometimes eat plant roots or seedlings, and the plant will appear wilted. Look for a slime trail similar to the kind slugs and snails leave behind. If you can see a trail, it's likely that there are gnats in your indoor plants.

Gnats also like light, so you may notice them on your windows, particularly if houseplants are nearby. 

Gnats are often confused with another garden pest: the common fruit fly but the two insects are completely different. Fruit flies will linger mostly around fruit, and unlike fungus gnats, are tan in colour and look like oval, iniature versions of the house fly. 

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3 ways to get rid of gnats

If you notice signs of gnats, it's important to take steps to get rid of them right away. 

While you could play the long game and buy a few carnivorous house plants to combat the problem, there are three easier ways to quickly eradicate adult gnats flying around your indoor plants.

1. Create a DIY gnat trap using vinegar

• Place a tablespoon of sugar in a bowl.
• Add 2-3 drops of sweet-smelling dish soap and a cup of white vinegar to the same bowl. Cover the bowl tightly with cling wrap.
• Poke several small holes in the cling wrap. Place the bowl close to the house plant and allow it to catch flies overnight.

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2. Use sticky fly traps

If the smell of vinegar puts you off creating your own DIY gnat trap, another option is to buy sticky gnat traps. These traps can be hung from a branch of the plant, or placed directly into the soil to catch any unwanted critters. By reducing the adult population, you'll also reduce how many eggs are laid in the soil of your plants.

Check the traps every few days and replace when they become covered with gnats. Avoid touching the plant leaves with the sticky paper. 

Keep an eye out for traps that are non-toxic and double-sided for maximum effectiveness. 

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3. Use an indoor fly catcher

Not your first time dealing with gnats in your houseplants? Then you may want to invest in an indoor fly catching device.

These devices are usually USB powered and use a combination of LED lights and fans to attract and suck flies into the trap.  

Kogan

USB chargeable smart LED UV mosquito and insect catcher, $65.04, available at Kogan.

How to prevent gnats in indoor plants

While getting rid of adult gnats is a great first step, that's often only a short-term fix. More adults will appear from the larvae in the soil. A better approach is to target the larval stage of their life cycle by allowing the soil to dry out. Because gnats lay their eggs in the moist soil around plants, reducing excess moisture is a key to getting rid of these nuisances for good.

1. Avoid over watering - Allow the soil to dry between regular watering - not to the point that your plant begins wilting but enough that the soil isn't continually moist. The eggs and larvae usually die in dry soil. 
2. Choose a pot with good drainage - A pot with good drainage will prevent gnats from laying eggs in the soil and will also protect your indoor plant against common problems such as root rot. Remember to drain any excess water that may have accumulated in saucers.

WATCH: Graham's top tips for choosing the perfect pot for your plants

Other ways to prevent fungus gnats

Fungus gnats are often more noticeable in autumn. It may be that they hitchhike on plants when they're brought indoors at the end of summer.

Before bringing plants inside, check them to make sure they're free of insects. Before you purchase new plants, examine them to make sure there are no insect infestations. Use a sterile potting mix when planting or re-potting.

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