image of 5 plants coming indoors

8 Ways To Kill Fungus Gnats In My Houseplants

Along about this time of the year in Ohio, I start thinking about how to kill fungus gnats in these plants that I have summered outside. Which will be allowed to come back inside for the winter? Visions of swarming gnats come to mind and I start thinking about how to kill fungus gnats in my houseplants?” Here are 8 suggestions.

image of pothos plant in basket
Getting ready to kill fungus gnats

This year I am sticking with what I think helped the most for me last year. That would be a Systemic Insecticide that is put into the soil and drawn up through the roots of my plant. I am using the Bonide Systemic Granules which is a granular powder that you will put in the soil of your houseplant pots.

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image of head vase planted with String of Pearls
My String of Pearls & Bananas can’t be eaten by gnats

As you will see in my video, I am readying my plants to bring inside by adding the required amount of Bonide Granules and mixing it into the soil prior to watering the plant and rinsing it well after a good inspection. Always be sure to inspect the houseplant to make sure no “critters” are coming inside by hiding under the leaves or in little crevices.

I like to spray them off with water too, both the plant and the container. Be sure to check the bottom of the pot as some critters like to crawl inside the drainage hole and set up housekeeping. Get them evicted!

Understanding the Life Cycle of the Gnat

Adult Gnats once hatched will live for about a week to 10 days and will try and lay as many eggs as possible during that time.

Adult Gnats lay from 100 to 300 or more eggs during their lifetime. That means a lot of chances to increase the swarm around your computer screen.

The eggs hatch after about 3 days, then schlup around in the soil for about 2 weeks before they emerge as adults and ready to start laying more eggs!

Besides being very annoying, the larvae of these gnats feed in damp soil in your houseplants. They look for decay and can eat roots of plants causing wilting and yellowing of leaves. This can contribute to root rot.

If one gnat can lay 300 eggs, and those 300 gnats lay 300 eggs each, in a week or so you could have 90,000 gnats flying in your face from just one gnat. <shuddering>

closeup image of fungus gnat and we want to kill fungus gnats

What about indoor plants that STAYED indoors?

I am planning on the same treatment with the Bonide Systemic Insecticide indoors just the same as I am treating the outdoor plants as I bring them inside. As the instructions say on the container, it is necessary to repeat the application into the soil about every 6-8 weeks. It is another job to do.

But would you rather swat gnats out of your face? It is necessary to start early before the gnats get a firm hold in your houseplant soil.

image of my swedish ivy and wandering jew plant combo
Can I kill the fungus gnats if I bring inside?

8 treatments for Gnats In Houseplants

The Bonide Systemic Insecticide needs to be mixed in the soil where it can then be distributed through the plant via its own roots, stem, branches in the plants own fluids. If the larvae eat the roots, they die.

Treatment is repeated about every 6-8 weeks throughout the winter and spring. This works best for me and helped so much last year.

Moisture is what attracts the gnats and entices them to lay their eggs. The larvae thrive in the dampness. Let your plants dry out thoroughly before they are allowed water. (Within reason for those moisture lovers.)

Even if you bottom water, those sneaky gnats will find the dampness in the saucer and go into the drain holes. They are sly little suckers!

Regular 3% Hydrogen Peroxide can be mixed as a watering solution. Use 1 part HP to 4 parts water. Mix just when ready to use. This can kill larvae in the soil to stop the cycle of gnats from hatching. Be persistent.

Neem Oil solution is said to kill the critters too, so spray the soil surface and mist the bottom branches to ward off the adults. It has a weird smell but it fades quickly to me.

Cinnamon is anti-fungal and can kill the fungus that the larvae like to eat so sprinkle the surface of the soil with cinnamon. Ceylon cinnamon is said to work for this best

Use those yellow or any color of Sticky Pads to catch the adults as they fly around. I leave them around all my shelves and stick them in plants all over. Just seeing all the little corpses stuck there is so pleasing.

Gnats are known to be poor flyers, so you might keep them from getting too “frisky” if they can’t get around very well. It sure is worth a try.

I am plugging a fan in to run with my Grow Lights on a timer. ( Maybe I will get stronger plants too, as a bonus. A gentle wind is supposed to make sturdy stems, right?)

Mosquito Bits are an option to use as a “mulch” on your soil surface. When you water the BT will wash through the soil, killing the larva. I didn’t care for the way it looked and it does mold. You can also rinse the Mosquito Bits into water and then use that to water your plants.

Also my little Dachshund liked to eat the Mosquito bits from the pots if she got a chance. Thought she was poisoned but she wasn’t luckily. Guess she thought it was kibble in the dish!

image of large flapjack plant
My Flapjack has pretty colors, but let’s kill the fungus gnats please.

Well, that’s all I have for now. I hope that helps you to conquer your gnats this year. Just be sure to get started early so that when your plants do come inside, you will have a head start on keeping the gnats away.

Remember it is an on-going process. They won’t disappear overnight. It may take a month or more to lower the population. Please know that when you first bring the plants inside, gnats may take a while to show up, just be sure to use a least a few of these suggestions as preventive, and then go full bore if or when it becomes necessary.

image of my campanula and a trailing jade
Trailing Jade has been growing so much this year.

Good luck. Let’s get ’em!

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