Ok....you need start with a blank slate because much of what you've been reading is bad information. The vinegar trick won't work for fungus gnats.....that's a fruit fly trap.

I believe that cinnamon is recommended to kill fungus in the soil (at least that's what some have explained) . Fungus gnat larvae don't feed on fungus.

And it's impossible to allow your soil dry out to the point that it will no longer support these insects. Your plants will die first! You are right to understand that you cannot withhold water, especially with a peaty mix like MiracleGro. Be more conservative....but don't let the plants wilt.

Covering the top of the soil with sand or gravel is to prevent the adults from laying eggs. I'm not really sold on it.

That leaves the mosquito dunks and gnatrol, both of which control the larvae with the exact same active ingredient. Bacillus thuringiensis isralensis (Bti) . Harmess to people, plants, and other animals, it is perfectly safe to use in veggie containers. I far prefer the Gnatrol, which will be easier to apply at the right rate than the dunks, which have to be soaked in water blah blah. Again, it's perfectly safe to eat the vegetables.

You might consider the gnatrol plus a layer of sand. Moss won't deter them.

Changing your potting medium will solve the problem. I haven't seen a fungus gnat in over 20 years! :-)

Gnatrol is a good product for a gentle knockout of the larvae and will give you the control you need. It does not kill adults, so be a little patient if you continue to see them for awhile because the chain will be broken when there are no more larvae to become adults. Miracle grow has so many different labels for 'potting soil' and each a bit different. Some retail potting soils even contain water retention gel and that may be adding to your situation. You can grow plants in peat based soil with no fungus gnat problem but you really have to get a handle on how to water. Too much water is not the same as too often water. Air moves through soil by wicking or capillary action and to do that it has to alternate between being wet and drying out. As rhizo says, however, in your situation, with large pots, it would be difficult to get any consistancy of properly moist in your conditions. Read your gnatrol label and follow it.

fungus gnats are an insane INDOOR PROBLEM ... in winter ...

why are they an issue out doors in wind ...

do they actually have the potential to kill a large plant???

learn me up some!!! ...

ken ...

It's the potting medium, ken. The fact that petron is on an upper floor of his/her apartment building might be a factor, too. Where else are the adults going to go BUT those containers?

A heavy infestation of fungus gnat larvae may weaken an otherwise healthy plant....I'm not so sure about killing it. Unfortunately, a serious population goes hand in hand with either overwatering or a crappy medium or both. Add the fungus gnats to all of that and you probably have some dead plants.

Yes, it can get to the level of severely weakening a plant and eventually killing it. On poinsettia crops (winter grown and not in the best of weather) it can be a major issue. The larvae will not only start eating the roots, I have found them moving up the stem like a borer and of course it blocks flow and kills off that stem. I didn't have them on points in my own facility, but sure dealt with it when I worked for another because of the help not allowing the planting medium to dry out. On young starts of bedding plants, it can just ruin them so they never thrive and succumb to other diseases. Our plant inspector would not gig a house for them until they reached a certain level, but when the population pressure is high enough, they'll eat the roots......not to mention the soggy conditions invite all sorts of root rot issues.

They can be a problem in containers - period. Inside or out. I've had them in seed flats outdoors more than once, Ken, hard to control the amount of rain we get in Spring so outdoor flats have to reach some happy medium between too fast draining for the seedlings and staying moist enough to support the gnats. BTi found in Gnatrol, Knock Out Gnats, mosquito dunks too takes care of them,

Petronilla, you've gotten some very good advice above. Just be consistent with the BTi product and you'll get control. It will take some time to stop the breeding cycle so be patient....Don't bother trying to kill the adults in the meantime, they don't live that long and don't harm anything themselves, its the larvae in the soil that you need to be concerned about. The layer of sand may or may not help, I've watched the adults go in and out of drainage holes pot bottoms to lay their eggs :)

And please never put bleach in a pot containing plants, the ph of household bleach is something like 11, you'd be better off gambling with the gnats.

Fungus Gnat larva need an environment that has moist organic matter to live, grow, and become the short lived adults that lay the eggs that become new Fungus Gnats. About every university web site I have seen about Fungus Gnats will tell you that allowing the top 1 to 2 inches of the potting soil to dry out between watering is of great help in control of these wee buggers. This is from the UCDavis web site linked below,
"Cultural Control
Fungus gnats, shore flies, moth flies, and March flies thrive under moist conditions, especially where there is an abundance of decaying vegetation and fungi; avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Clean up free-standing water and eliminate any plumbing or irrigation system leaks. Moist and decomposing grass clippings, compost, organic fertilizers, and mulches are favorite breeding spots. Avoid using incompletely composted organic matter in potting media unless it is pasteurized first, because it often is infested with fungus gnats. Minimize organic debris around buildings and crops where larvae feed. Avoid fertilizing with excessive amounts of manure, bloodmeal, or similar organic materials."

Here is a link that might be useful: Fungus Gnats

This is such a lovely community! Thank you everyone for your wonderful responses. My husband and I are learning so much!

So, we will be a lot more controlled with our watering, and I will never again use Miracle Grow - I knew when we bought it we were taking our chances, but also we were trying not to spend too too much money on this experiment (i.e. soil). We are really enjoying our garden and visit with our plants daily :), so, we most definitely want this to be a long term investment.

One last question: We didn't exclusively use Miracle Grow, we also used a Miracle Grow organic choice soil and wanted to compare the growth of the plants in both pots. It seemed that some of the plants weren't doing so well and our local (and really great garden store) recommended the following fertilizer: Dr. Earth Tomato, Veggie, & Herb Fertilizer (they do not for example carry Miracle Grow and mostly all organic products, chemically free). The Dr. Earth is a 5 / 7 / 3, with calcium and sulfur. The primary / secondary nutrients list starts off with fish bone meal amongst a number of other things.

The gnats seemed to have gone crazy shortly after we fertilized. Anyone want to speculate on whether or not it is the soil or fertilizer (I read somewhere that bone meal could cause gnats too), or, is the combination of soil, watering, etc. too difficult to speculate?

I'm thinking about when we need to fertilize again and wondering if some other product might be better.

We will go and get the gnatrol today and be very vigilant about using it. I'll make sure to update everyone on our success!

Thank you once again.

ow.. ow... ow... man i asked you teach me.. but now my head is hurting.. lol ...

OP...fert did not cause this problem..

its your watering regimen... let the pots dry more..

do NOT water a plant.. until is starts to droop .. that is called letting it dry ... one day of droop will not hurt a plant ... and then water sparingly ... and if you keep a journal.. you will find out how long it takes each pot.. to dry completely ...

and then compare that.. to how often you water them ... and i bet you will be startled ...

on some level.. this might fit within the definition of LOVING YOUR PLANTS TO DEATH ....

and do it for every plant ... every pot is different ... do not treat them all the same ...

and personally ... on any plant that is not a FOOD.. i would go chemical.. and get rid of the problem ...

there are peeps in the hosta forum who do pots.. and there is the famous Al's gritty mix ... if you use the GW search engine ... there is a lot of science behind proper media [not soil] .... and you are relying too heavily.. on some manufacturers description of their own product ...

BTW.. what does your beloved nursery.. use in their own greenhouse???

ken

Additional nutrition is necessary for potted plants, but yes adding it can push the odds toward fungus gnats, drain flies etc. If you ever worked in greenhouses, you will often notice algae growth on the glass or plastic behind the benches where supplemented water is used, but nowhere else. It's just like eutrophication in a pond.......the nitrogen feeds algae growth, and algae growth provides food for fungus gnats and drain flies. If you see a green or black scum on the surface soil of potted plants, it's algae fresh or dried.

Actually, ken, it's important that the containers be watered pretty thoroughly when its time. If not, the whole volume of roots/soil may not get saturated. If that occurs, hydrophobic dry pockets will form....ESPECIALLY with a mucky sort of potting mix such as the MiracleGro.

That's why we strongly encourage the use of a very porous, fast draining mix. Such a medium can be watered frequently with no fear of overdoing it or fungus gnats. There are commercial media available that fit the bill (I use one that is bark based), or you can learn to amend an ordinary mix, or you can build one from scratch.

By the way, Petron, when you get the Gnatrol please understand that you mix it up and apply it when your plants need watering. Don't water more often just to treat the gnats. That would be like shooting yourself in the foot....but you'd be surprised at how many people do just that.

Fertilizer choice won't have any effect on fungus gnats, just the plants. I disagree about using wilt as an indicator of when to water or as an attempt to get rid of FG's. About to wilt = healthy, actually wilted = extreme distress. As plants grow, they will use more moisture so the pot will dry more quickly, so a set schedule is rarely ideal.

Drying at the top really won't help since the gnats will just use the moist soil at the bottom of, and within the center of the pot, especially if they are able to access the drain holes as mentioned. (Assuming your pots have drain holes. Do they?)

The only bone of contention I have, a very minor one, with the excellent advice here would be that I wouldn't call a potting mix crappy if the only reason for that label is that it is able to support fungus gnat larvae. They need organic matter, so although it's certainly possible to have/make/(buy?) a potting mix without such, many people are perfectly happy with potting mixes containing such, either store-bought or home-made. Since fungus gnats are so easy to defeat/control/avoid, I don't find this one feature, seeing a few fungus gnats in small enough amounts that they do not bother plants or people, a significant enough detriment to call a potting mix crappy. (Please don't interpret this as arguing that FG's can damage plants, not saying that, just that a few seem harmless.)

Some don't tolerate any fungus gnats, and I respect that, and support their efforts to get rid of them. Some may create a mix that does have organics but not of a type/texture that harbors FG's. As you learn, you can do the best possible job with what you can get and afford.

Instead of overwatering, think under-drying and excessive moisture within the "soil" as the issue. I water many plants daily, if I feel like it, although they can go for a few days, some longer...

Petronilla, FYI ,,,, I grabbed a bag of the MG Organic potting soil a few years ago, my local garden center was out of the Cornell 'recipe' potting soil that they normally mix, bag, and have on hand. I found it heavy, comparing it to what I am used to using and even comparing it to regular MG...

I wanted some that day to pot up some perennials into larger growing-on pots and they were just in that medium until Fall so no harm done long term - but again, I found the organic product a little dense and heavy, certainly no better than the other products under that label so still somewhat marginal.

Entomologists at most all of the agricultural research schools that have written about Fungus Gnat control tell us to allow the top inch or two of soil to dry out to help control these wee buggers and since the Fungus Gnats need a fairly airy, although moist soil, they will not move deeper into the pot, according to the entomoligists I have talked with.

I have gotten fairly decent control, just by taking a kitchen fork and 'cultivating' that layer to let air in when working with peat based soil mixes. It is true that they inhabit the upper layers of the soil. The heavy soils in some OTC bags have other problems of their own as far as root aeration.

Haha, this last comment is the best. I've a bunch of houseplants one of which caught the gnats. My boyfriend found it hilarious that I use a wooden skewer to stir round the top layer of soil and scare them up, at which point I would either whack them or use a dustbuster to whack them. He's greatly amused by me spending 10 minutes staring at these plants. Glad to see I'm not the only one obsessively coaching the wee plants.

To keep watering plants while treating I have been known to stick a straw in the soil, and use a tiny funnel in the top of it to pour water in slowly, this then goes in about 3-4" down leaving the top dry. (I have the funnel from a travel refill cosmetics kit for Muji). For larger pots I also used a breadknife, stuck down the side of the pot the push the soil out slightly and make a channel to push water in.

Currently I have been using yellow stickies traps and something from the garden centre called "bug killer" I spray it on the soil every 10 days or so. Its scared a load of flies out onto the stickies in the following 24 hours. I repotted the plant into a different pot, knocked off the top 2-3" of soil, put it in a bigger pot, and added 4-5 inches on the top. I though this would bury the remaining gnats down deep. The new pot had drainage holes in the bottom to water, to allow the top to dry out. Instead the little buggers are now coming out the drainage holes in the bottom! Much lower numbers, but still there. I will add some of the spray to the water next time I water it from the bottom. I think they may have spread to another indoor plant, so obsessively checking the top soil of all plants now before I water...

If anyone has other things that have work, please let me know. I know they do no real damage, but having the little feckers flying round the house is driving me mad.

I accidentally murdered a whole emergence of them--I had a loose plastic bag over a couple twigs I was rooting to keep things humid (obviously too humid). The adults all ended up stuck to the misty bag.