Houseplants forum→Fungus Gnat Hell - Please Help Me!

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Nov 7, 2020 2:56 PM CST
Hi everyone! I'm new to this forum but I've been taking care of my houseplants very well for a few months now. By some reason I still haven't identified, one of my newer houseplants I brought home must have had fungus gnats. The infestation has practically spread to all of my plants at this point.

My houseplant care had been going so well that I didn't even realize the gnats were a pest- I thought they were fruit flies. I've been trying some methods I found online such as spraying soil periodically with a diluted soap/alcohol mixture, letting the soil dry out, placing rocks/stones on top of the dirt to prevent them from coming out, etc. Unfortunately none of this working. I also have started bottomwatering my plants, but that still has done next to nothing.

For some additional information on my situation- I currently live in the midwest. We are experiencing an unusual week of warmth but after this week it will return to normal November cold temperatures. I have cut back on watering my plants due to the cold (and with many of my plants entering dormancy). To combat the gnats I have been letting them dry out and watering them at that point (about once per week). My plants are all located in areas near a window where they can receive ample sunlight when it is out. When it is cloudy or overcast I have grow light setups to provide them with light. None are located near drafts or overheated locations. I have a wide range of plants - pothos, bonsai, caladium, tradescantia, succulents, etc. (not sure if this information will help but I'm adding it anyways)! The succulents have not been bothered by the gnats, most likely because their soil stays fairly dry and drains easily.

Do any houseplant pros/veterans have any more long term solutions to this? None of my plants have died yet as a result, but I am starting to think that two of my plants have it worse than the others. I am getting tired of removing the adult gnats every single day and have them in almost every room of my home - even those that don't have plants. I don't want to get rid of my plants either, as aside from the gnats, they're doing incredibly well.

Please help me out! I'm at my wit's end!
Name: Lin Vosbury
Sebastian, Florida (Zone 10a)

Region: United States of America Region: Florida Charter ATP Member I was one of the first 300 contributors to the plant database! Million Pollinator Garden Challenge Garden Procrastinator
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Nov 7, 2020 4:15 PM CST
Hi plantol, Welcome!

Fungus Gnats are usually present when the soil is retaining too much moisture and depending on the type of soil being used, watering once a week may be excessive. I always advise to pour water atop the soil until it begins exiting the drainage holes, empty any excess water from the tray and don't water again until the top two or so inches of soil feels dry when you stick a finger down into it.

Some plants may need to dry longer than others. Devil's Ivy (Epipremnum aureum) for one is fairly drought tolerant and once a week watering to me sounds like too much. I don't grow Caladiums (Caladium) as house plants, they are landscape plants here in the south and it's normal for them to go dormant. If you continue to water, it will likely rot the bulbs.

How are your plants potted? Pot size should be kept to the smallest size possible, just large enough for the root mass and soil; pots too large will cause issues with proper watering. Although many add pebbles to the bottom of the pot, that habit is detrimental to the health of plants; adding pebbles, pieces of crock, etc. does nothing but deter proper drainage. I'm not sure what you mean by bottom watering your plants but having water so close to the roots, especially if they are already waterlogged, will cause rot. I'm thinking you might need to allow a longer drying time between watering.
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!

Name: Bria
Northern VA (Zone 7a)
Houseplants Birds
Nov 7, 2020 6:13 PM CST
I used gnat sticky traps that I got from Amazon when I had a bad infestation. They worked GREAT!

It took care of the immediate problem of infuriating bugs flying around and gave me a chance to get a handle on my watering and soil issues. No problems now!

Good luck!
Name: Kevin Langley
London UK
Nov 10, 2020 11:34 AM CST
Fungus gnats are a pain.

There are several things you can do or do all.

Get sticky traps.

Get a plant saucer that has some depth and fill it with some cheap beer or wine cover the top with Saran wrap/plastic wrap and make holes in it, the flies will be attracted to it and fly in and drown.

Get some mosquito repellent.

Get some worm castings and mix that into the soil.

Collect some Rove beetles or centipedes, they love hunting fungus gnat larvae.
[Last edited by AmberLeaf - Nov 10, 2020 11:36 AM (+)]
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Name: Sabine
New Mexico
Nov 10, 2020 2:54 PM CST
I've used azamax with great success. It is a pesticide based on neem oil (non-toxic), but the active ingredient is concentrated and it doesn't smell. Two applications and hardly any more gnats.
NW Wisconsin (Zone 4b)
Region: Wisconsin Dahlias Butterflies
Nov 10, 2020 3:05 PM CST
I use sticky traps as well as this: if you have a small half pint jar mix about a tablespoon dawn dish soap with a tablespoon apple cider vinegar - stir until mixed and place the jar amongst my planters. The bugs like the stink and fly in and drown.
I hear the passing echoes of winter and feel the warming spring on my face. ~Terri Guillemets
Boston, MA (Zone 6b)
Nov 11, 2020 8:01 PM CST
Hi Plantol,

I too have experienced fungus gnat hell and offer my deepest sympathies.

For what it is worth, I tried what felt like every trick in the book before finally finding success with a combination of yellow stickies for the adults and Mosquito Bits ( for the larvae. I sprinkle a few granules of MB into my watering can and let them sit overnight before watering the next day.

This is also complete overkill, but at some point I got tired of the yellow stickies -- I have to admit I've made a lot of mistakes over the years that lead to gnat resurgences... -- and upgraded to a Katchy for the adults ( I've found it to be very effective and unobtrusive.

Good luck with the gnats!

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