9 Tricks to Finally Get Rid of Fungus Gnats on Your Houseplants
When it comes to pests that show up on houseplants, fungus gnats aren’t the most concerning. At least, they don’t seem to be, but things aren’t always as they seem. While the adults won’t do any harm, their larvae can do serious damage to plant roots. They can also be an indication that root rot is on the horizon.
Both larvae and adult fungus gnats can carry pathogens for diseases like black root rot, Verticillium wilt, and Pythium blight. The larvae feed on roots, which may stunt growth and lead to a lack of nutrients, which can cause leaf yellowing and death.
While they aren’t harmful to humans, these pests can harm your plants over time. I find them to be unsightly and quite a nuisance. If you, too, don’t appreciate having these guys around and struggle to get rid of them, we can help. I’ve got some easy solutions for getting rid of annoying fungus gnats and warding them away from your houseplants in the future.
Hydrogen Peroxide
Since the larvae are the most concerning issue, it’s a good idea to start there and then worry about the adults next. It’s more effective to combine two or more of these methods as most of them only work on one or the other. Hydrogen peroxide is helpful in eradicating the eggs and larvae, so you can protect your roots using this method.
The entire lifecycle of houseplant fungus gnats is about three to four weeks, so you must be persistent to get rid of them. The adults lay eggs in damp soil, which hatch in about three to four days. Then, the damage begins. Larvae spend the next two weeks munching on root tissue. They spend three to seven days in a pupal stage near the surface before hatching as adults. Adult gnats have a lifespan of about seven to eight days.
Hydrogen peroxide kills the larvae and eggs on contact. While it won’t affect the adults, repeating this treatment several times over a series of three to four weeks should solve the problem. You may see results from this method in as little as one week. But it’s a good idea to repeat it once or twice anyway, just to make sure.
Don’t pour that peroxide directly on the soil or splash it around; it can cause leaf burn. Aside from that, hydrogen peroxide is not harmful to your roots and, in fact, can be helpful. It not only eliminates the eggs and larvae, but it can also oxygenate the soil, which speeds root recovery.
Create a solution of one part peroxide with four parts water. That would look like one cup of water to one-quarter cup of hydrogen peroxide. Pour this solution evenly onto the surface of your potting material. This will eliminate the eggs, larvae, and pupae.
Since it doesn’t kill the adults, there is a chance that they may lay more eggs that could survive. For this reason, go ahead and repeat your treatment at about seven to eight days. This will get rid of any new eggs as the original generation reaches the end of its lifecycle.
Sticky Traps
You may know about yellow sticky traps from dealing with whiteflies or other flying insects. Well, they work for the adult gnats as well! The adults are attracted to the color yellow like most insects are. The super sticky coating on yellow sticky traps captures the adults when they land on it, and they can’t break free.
While this solution won’t get rid of fungus gnat eggs already in the houseplant’s soil, it’s great to use in tandem with hydrogen peroxide. You eradicate what’s under the soil and trap the adults so they can’t lay more eggs. Using these two methods together is a good way to get rid of them in a shorter time.
Depending on the size of the plant and the number of pests, you may need more than one per plant. If you’re dealing with a larger plant, hang your traps in the canopy. In smaller plants, set the trap inside the edge of the pot.
For a bad infestation, you may have to change out your traps once or twice. But, one will usually do the trick in combination with a second method of control.
Neem Oil
I give this treatment hesitantly. While neem oil is helpful in dealing with houseplant pests, it’s not necessarily going to be the most effective solution for getting rid of fungus gnats. However, it won’t hurt if you have some around and want to try this before you take other measures. It can help but may not do a thorough job, and you’ll have to repeat it.
Neem oil is a naturally derived insecticide and fungicide. Its fungicidal properties make it helpful in conjunction with the other controls, so it’s not without merit. It can be messy, though, and the smell is one that many gardeners find unpleasant.
Spray the neem oil down your entire plant, leaves, stems, potting media, and all. You can dilute it with water if you want to use it as a drench for the soil. Use the same 1:4 ratio that you would with hydrogen peroxide. You’ll want to repeat this process a week later and, if it doesn’t completely eliminate them, possibly once more.
Mosquito Dunks
Mosquito dunks are small disks containing a biological control that release the bacterium Bacillus thuringiensis israelensis into water. Its most common use is in standing water outdoors, like birdbaths. It kills mosquito larvae, and it does a good job of it.
In the same way that it kills mosquito larvae, it will do the same to get rid of your indoor houseplant pests like fungus gnats. This bacterium is lethal to many insects but harmless to humans and pets, so it’s a safe and easy method of control. It won’t eliminate the adults, so it may need repeating.
You can leave some dunks in your water can to deliver some of the bacteria into the soil, but this is not the most effective method. The most effective and long-term method is to crush the tablets and sprinkle them over the soil. This way, when you water, the bacterium releases into the water and kills the bugs. They should last for several weeks, which will ultimately take care of several generations.
Diatomaceous Earth
Diatomaceous earth is a great tool for gardeners, as well as anyone with pets or other outdoor animals. It’s also good for feeding larger animals to eliminate parasites, though you should do so under the counsel of your veterinarian.
This fine power comes from the skeletons of fossilized algae. The algae are ground into a powder, but the edges are sharp and pierce the exoskeletons of small insects. The insect then loses moisture and dies of dehydration.
You can mix a bit with your potting mix when you pot your plants initially. However, it loses effectiveness when wet. The best way to use it is to sprinkle it on the surface of the soil. This is more effective in killing adult gnats as they come in contact with the surface. For this reason, it’s one of those treatments that you should use alongside another, like peroxide.
Allow the Soil to Dry
For plants that can handle some drying out, allowing the soil to dry between waterings is a decent way to reduce the occurrence of these insects. Because they lay their eggs on moist soil, when the top is dry, they will look elsewhere.
Allow the surface to dry out between waterings. If you mix some hydrogen peroxide or neem oil with your water, the two methods are more effective than one.
Re-Pot in Fresh Soil
Re-potting your plant is going to be among the most effective ways to eradicate fungus gnats. You’re effectively getting rid of three stages of the life cycle, and then you can make things less hospitable for the last one to reproduce. You will want to be thorough about it, as you want to work all the pupae, eggs, and larvae out of the root system.
Remove the plant from its pot and shake free all the loose soil. If you have a lot of potting mix stuck in the roots, give them a gentle but thorough rinse in cool water. As an added measure, you can spray the clean roots with a solution of one part hydrogen peroxide and two parts water.
Rinse out the pot completely, and while you’re at it, spray it down with that peroxide solution to make sure you’re getting everything. Then, re-pot in fresh soil and maintain good watering habits as a preventive measure.
Use Sand
Fungus gnats need to lay their eggs on a moist medium. Since sand drains quickly and doesn’t retain moisture, you can use it to prevent adults from laying their eggs to begin with. While this won’t eradicate the existing larvae, pupae, and eggs, it can be an effective preventative.
This one is simple and easy. Use horticultural sand, as builder’s sand can be too alkaline due to high lime content. Spread a thin layer on top of your potting mix. About a half-inch thick should do the trick.
Maintain Good Watering Habits
Finally, going forward, you should strive to maintain good watering habits. This is the single most important factor in caring for houseplants. Overwatering is the most common cause of houseplant death. It causes root rot and creates a more hospitable environment for harmful pests and pathogens.
Watering will vary from one plant to another, depending on their specific needs. While some may need consistently moist soil, most plants prefer their soil to dry slightly between waterings. Let the surface of your soil dry between, this will go a long way towards fending off these pests.
