Fungus gnats are attracted to excessively moist/wet soil. Thus, your either over watering your plants or your soil is too water retentive.

For the mean time taking a chunk of a mosquito dunk and letting it dissolve in your watering can for a night then watering your plants throughly kills all the babies in the soil. As it has BTK which only affects and kills gnats.

What plants are we talking about?

Hey! I have so many plants, it is hard to list them all. But the perlite on the surface definitely stopped the infestation. The ones where I noticed they stopped throwing up new shoots are wandering jew, in paricular (have a couple of those). Could the perlite be impeding the shoots coming through on the surface?

Is the perlite matting together as a crust?

Wandering Jew, for me anyways, never sends up new shoots from the soil line. My new shoots either come from cuttings or sprout from existing stems.

If the perlite is still fluffy and loose, it shouldn't be hard for new growth to push through it. Yet, I have very very little experience with perlite in general.

I don't think the perlite is matting together as a crust. I just inspected the wandering jew and noticed that what I thought were new shoots before were actually just new branches from the original shoot near its base. So I don't feel as bad now! Thanks everyone.

Perlite won't stop plant growth. But for Fungus gnats:

Buy
a package of "Mosquito dunks" at the garden center. Put one
quarter of one in your watering can. This will kill the larvae in the
soil and stop future generations. It is all natural and safe. Use
sticky traps and manually kill the adults.

I have peace lilies will perlite help with the larvae eggs in the soil and kill fungus gnats will it hurt my lilies.

Perlite will not help with fungus gnats. For that, buy a package of "Mosquito dunks" at the garden center. It is BT. Put one quarter of one in your watering can. This will kill the larvae in the soil and stop future generations. It is all natural and safe. But give it some time to work. Use sticky traps and manually kill the adults. Oh wait, I already replied the same thing earlier.

Maybe this person is thinking of pumice. I have seen those confused more than once. As a top dressing, pumice can inhibit fungus gnats. It's sharp like shards of glass to them.

The mosquito dunk system is a good suggestion!

Just want to clarify that perlite on the surface of my plants DID indeed control the fungus gnats. No, it does not kill them, but they will not lay eggs in the perlite. It must deter them from going underneath it into the damper soil. It 100% worked for me on every plant I tried it on, and I have given the advice to my other plant-loving friends who have used it with success. Just responding in case anyone else reads this thread in future. I’m sure those mosquito dunks work to kill the larvae, but the perlite stops the gnats from laying eggs so will also work to stop the problem in its tracks.

Because conditions (wet/soggy soil with rotting organic matter) the bugly uggers find so inviting generally bar the plant from realizing its full potential, it would be best to eliminate those conditions. Better to avoid using overly water-retentive media and make sure watering intervals are appropriate. Avoiding organic fertilizers like fish/ seaweed emulsions or meals, as well as other assorted meals (alfalfa, cottonseed, blood, hoof, horn, feather, bone, etc., can also deny the gnats conditions that send them into an orgiastic frenzy.

The reasons fungus gnats become problematic are media that remain wet near the surface for prolonged periods along with organic matter that breaks down readily. If I had to reason my way through the problem, that's where I'd be focusing focus my attention ..... if I had trouble with gnats. I don't, because I use exclusively, well aerated media the gnats do not find attractive, and a soluble synthetic fertilizer.

Al

@tapla (mid-Michigan, USDA z5b-6a) - would you mind sharing what type(s) of soil you use? I have recently started having some succulents in my house - and I must have brought some fungus gnats home with my last purchase. I almost have them under control - I am ordering some mosquito bits/dunk to solve the problem. I’ve never had fungus gnats before - I used to have a collection of about 8 plants, but have only recently started up again with attempting to develop a green thumb!

Thanks!

@dani_m08 I use two basic media I make myself. In return for the effort it takes to source ingredients and put the media together, I get media that allows me to water to beyond the point of complete soil saturation with no need to be concerned that I might be over-watering, and a byproduct of highly aerated, free-draining media, which is the ability to have in place a nutritional supplementation program that requires no guesswork. The ability to always water correctly and maintain a sound nutritional supplementation regimen are essential parts of any care plan focused on maximizing your plants' opportunity to realize as much of their genetic potential as possible.

My initial foray into growing in pots was the result of an infatuation with bonsai trees. I was thunderstruck when, wandering around a hotel on a business trip, I discovered workers setting up a bonsai show. I fell in love with the diminutive trees and decided right than and there that I HAD to learn how to "do that". I set about chasing that goal but soon discovered I didn't have a clue, and was forever being frustrated because I couldn't keep my trees alive; so, I set the trees aside and hit the books, as this was all in the 1908s before the net was a thing. After about 3-4 years of fairly diligent study, I started over and was blessed by some newfound abilities. Since, I've been devoted to learning how to become more and more proficient in the art. Fortunately, as I learned about soil science and the plant sciences, almost all I learned could be widely applied to almost everything commonly grown in pots.

This is the soil I use for mostly succulents and trees:

It's made with pine or fir bark, a calcined clay (almost ceramic) product called Turface MVP, and grower size poultry grit or #2 cherrystone.

Below, is the mix I use for mixed floral plantings, veggies, and single potted plants other than succulents:

It's made from 5 parts of pine bark, and 1 part each of perlite and sphagnum peat, pl;us an appropriate measure of dolomitic (garden) lime.

Getting to the place where you can water correctly w/o worry that the soil will remain soggy so long it seriously limits root function or wrecks root health is a real game changer - likely the largest step forward a container gardener can take at any one time.

Over the years I've thought a lot about I've given a lot of thought to what represents the shortest route to a green thumb in terms of time and I always come to the same conclusion. It's knowledge. Learning by trial and error, getting bit on the butt by our mistakes, is a hard way to learn. This is especially true in light of the fact that w/o the knowledge to properly evaluate what we're seeing in our plants, we're pretty well doomed to repeat them. Also, our mistakes are often not made manifest until long after the error was committed, making it difficult to put together cause/effect relationships. It makes far more sense to learn all you can and then, use your practical experience (which would otherwise be devoted to trial and error) to validate what you already know. I promise you'll leave the trial and error crowd standing in your slipstream.

More often than not, swarms of fungus gnats are the result of watering intervals too short. Often, allowing the soil to dry down and checking moisture levels with a "tell" before you water is all you need to keep populations controlled.

Using a 'tell'

Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant.

Watering in small sips in order to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions - which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma and creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.

In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

One of the most reliable methods of checking a planting's need for water is using a 'tell' (more reliable than a 'moisture meter'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) works better. They usually come 48” (120cm) long and can usually be cut in half or in several pieces, depending on how deep your pots are. Sharpen both ends of each tell in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell's tip comes out nearly dry. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.

Al