For fungus gnats use mosquito dunks. I crush about a teaspoon or two's worth and mix in 5 gallon pails and water with it every time I water. It will not work overnight, but will kill the larvae. The flying adults will eventually die off.

Are your windows blocking UV light?

tj

Agreed. FG's aren't related to temps in any way.

If you could add a pic of the window in question, it might be help people help you decide how much light is coming in. Your situation sounds very common! Morning sun is plenty for many house plants, and should be enough for 6-pack Coleus. Are there trees or other buildings that block some of the light?

There are definitely Coleus for full sun but if the plants have been inside for a while first, they would need to be acclimated gradually to direct sun to be able to handle it without burning. Suddenly going outside for an afternoon could definitely burn a Coleus that would normally be fine in sun all day. Since you can't leave plants out there, I would probably not take them out at all. (Going outside also gives new FG's a chance to find the pot.)

Coleus do not revert, at least not that I've ever heard, but different amounts of light can cause a same plant to look wildly different. Some need more sun than others to maintain the wild coloring. In your situation, (any permanent indoor situation,) I would avoid the sun Coleus and go with the old standbys intended for shade (which include the wizards and rainbows usually found in those 6-packs.)

If you like Coleus, you may find colorful Begonias appealing also which are, IME, easier to keep as a house plant. Other colorful plants you might like are Alternanthera, Hemigraphis, Iresine, Cordyline, Hypoestes, Aptenia, Aglaonema, Calathea, Tradescantia zebrina or spathacea, Maranta, Peperomia, Pilea, Stromanthe. I'm not sure at this point which of these would work in your house, but the conglomerate of people here should be able to help you figure that out - with more info from you about the window/amount of light.

Coleus roots very easily in water. If you are having trouble keeping Coleus going in soil, the first thing I would do is take some cuttings to root in water.

Cold temps don't cause fungus gnats but what it could be contributing to might be that the plants' soil isn't drying out as fast as you are used to, so you may be watering the plants more than they need and the moist soil may be drawing the fungus gnats.
My experience has been that almost all plants (with a few exceptions) do better if you err on the side of letting them go too dry than too wet.

It seems strange that even plants grown in front of a window would look spindly unless your windows have some kind of coating on them to reduce UV exposure that is cutting down on the light that is useable to the plants.

Were you using an incandescent bulb for your grow light? Many people seem to have better luck with fluorescent or LED grow lights from what I've seen.

Excellent points, well said, Summer!

i use indoor systemic which works very well on gnats and a slew of other things like scale. i apply it also before i bring plants indoors in the fall - to assure that i bring no bugs inside.
i grow a lot of indoor plants on self-watering wicks - which means a lot of medium is moist - so gnats would be impossible to get rid of. but with this systemic it's no problem at all.
you could try putting down 1" of course sand on the top of ALL pots - that should at least prevent them from laying more eggs.

Here is a link that might be useful: bonide indoor systemic

This post was edited by petrushka on Thu, Apr 10, 14 at 16:00

Summer, I'd like to root them in water but the plants that will be for sale are in seed flats right now about to be separated, or cuttings that aren't sold until they are fully rooted. Would you put these in water and is there a risk to reversing the rooting process? There are no cut-it-yourself growers around here.
Purple I'll try to post a pic, but the house is L-shaped like a lot of duplexes so outside the glass a plant will have solid afternoon sun until it wilts and inside the glass no afternoon sun at all. Thank you all for your help.

Fungus gnats are a only a symptom of a much more significant underlying problem related primarily to soil choice and secondarily to watering habits. Get the soil right and it's hard to get the watering habits wrong unless you forget to water and let the plants dry out.

I wouldn't worry about fixing else, especially not with insecticides, until you explore the impact soil choice has on the return:effort relationship.

Here is a fairly thorough but still simple overview that will help you avoid all the most common pitfalls associated with growing in containers. If you find any value in that particular offering, I would suggest you spend some time learning about how water behaves in container soils, and why. Gaining an understanding of the information in the second embedded link probably represents the largest step forward a container gardener can make at any one time. I say that every chance I get because it's true; and so far, no one has taken me to task for expressing that opinion.

Al

Ok I'll take you to task. You are saying if I've had great success with certain brands and methods in the past (even plants a child can grow) which suddenly don't work in this house, it's because I need to be educated in the "one standard" of growing? Do the links you've provided have contingencies for my changed situation? Water clearly doesn't behave in container soils the same way in every environment, or a plant that has to be watered 3 times a day at the greenhouse wouldn't die of root rot at home with no watering at all. I didn't say I was using cheap soil, I said root rot kills the plant with just the moisture that comes when you buy it and a bag of potting soil. It's because of the standard care that young seedlings are used to getting that this is a quandary (like making sure it doesn't dry out), so clearly a radical change from the care they get at the grower is needed when they are removed from the greenhouse. Saying "it's hard to get the watering habits wrong" when one environment is so different from another is quite a statement.
Second, garden centers here are swarming with gnats and that's a problem. They also come out of the woods and one year it was hard to sleep they were so bad. So it's a symptom of their getting in the front door, we just happen to have plants and they spread from plant to plant. It's hard to understand your logic that they are a result of poor drainage when there is an infestation at the grower and those plants spread the problem, just as if it were aphids or scales. Gnats are plucky, or healthy well-drained plants wouldn't be carrying them.
I can tell you that gaining an understanding is something someone can spend their entire life doing and still have no way of knowing for example that my windows are blocking UV light. No one warns people who move here about the gnat problem. Does that make me a beginner? Lastly, it is because of the effort I have wasted that I am reluctant to make this investment again. If you could look at your own love of plants and imagine some strange circumstance making all your toil for nothing, I don't think you would use the words "effort relationship". It's hard to trust effort after that, it's easier to trust secrets of the trade that take effort away.
You know that when you say "no one has taken me to task" you're technically asking for it; people can mistake form-answering for being condescending. You have to understand that I've gotten advice from many places that might be similar to what is in beginner references, so I was hoping to hear from someone who has been in this specific situation.

Dont be discouraged just understand the garden center didnt tell you what was said by Al

Yet even when repotting in the " one standard way to grow things idea" soil is still making it easy to recant by the same persons who suggested it.

Even though idealisticly repotting a new plant is the normal for several to do here it is good advice for you but dont have hopes that a new soil is going to solve all your problems.

Who knows why things go wrong but when things do go wrong it's only because they where supose to (Murphy's laws)
Seesm you also know a solution as you said it yourself and you too are right

Enviroment: Take control of your indoor growing enviroment and your soil and you should have ( with no gurantee) sucsess

.... looks like you have all the answers you need. I hope you fare well.

When I said no one has taken me to task for suggesting that an understanding of how water behaves in soils is probably the largest step forward a container gardener can make at any one time, I wasn't inviting you or anyone to 'take me to task'. If you really want to have that conversation (about how important that understanding really is) let me know, and I'll happily oblige you. Can you think of a larger step forward a container gardener can make at any one time? A huge % of the problems people come here seeking remediation for are directly related to soil choice as a primary, and watering habits as a secondary. When you DO get the soil right, you actually have to work at over-watering. If you can't water to beyond saturation at will, you're dealing with soil limitations. There is no way around that.

And FWIW, how water behaves in media is governed by the laws of physics, so water DOES behave exactly the same way in any given soil in every environment with some minor allowances for altitude. Even changes in wind velocity and temperature don't change how water behaves in media except as it relates to the rate of evaporation or evapotranspiration.

The term effort:return relationship takes into account the quality of the returns you get for your efforts. Some people simply spin their wheels year after year, going through the same paces and getting the same return for their effort. Others, who might be willing to invest a little effort in learning how to identify and eliminate those factors imposing limitations on their plants are going to leave the 'it's always worked for me' crowd in their slipstream.

Best luck.

Al

len,
coleus and roses and avocado do not do well indoors, unless you have a giant se-s-sw window wall (sunroom).
it would be very useful if you could get a light meter - to understand what kind of light levels you have (from morning to evening and thru the seasons), measure your humidity levels too.
and then research what plants are suitable for your conditions.
as a quick practical solution - do use indoor systemic.
it will take you time to figure out what does or does not do well in your house, meanwhile you will be able to get rid of gnats.
keep your newly bought plants in sep room - treat them with systemic right away to prevent getting anything from nurseries. it takes 5-7 days for the plant to absorb it, so unless you spray the plants with insecticidal soap too, they need to be kept separate still for a couple of weeks.
if you plant or bring any plant indoors from outside - again treat with systemic a few weeks in advance.
also if you use miracle-grow soil - it is very often infested with gnats. throw in a few tb of same systemic and mix it in the bag, close-up, wait a week. then you can use it.
the systemic continues to work over 6-8 weeks period, so if anything will fly in from outside it'll die too.
from your description your plants require more light and less watering.
if you choose not to repot the plants in better draining soil (easy mix equal parts each soilless mix or peat, perlite, orchid bark) - at least keep them drier and in best light you have, by the windows.
care to mention what other plants you are growing?
do you have 'normal' tropical houseplants?
please, post some pics or describe your collection and window orientation, growing zone, climate,etc.

If fungus gnats are the only pest problem, a systemic is way overkill, like setting off a bomb to kill a mouse. The fungus gnats live in the soil, not on the plant. The mosquito dunks suggested originally are known to kill them.

Active ingredient in Bionide is imidacloprid. There is no way I would let this stuff on my property, let alone inside the house. According to the label, it's not safe to put a package of this stuff in the trash, and one should call poison control if it gets on your skin. I would strongly urge anyone with kids or pets (or skin) to avoid this stuff.

Thank you Petrushka for your detailed response. I didn't think of using orchid bark. This might sound strange but your mixture sounds like what I would use to germinate a mango seed or even reptile eggs, except that I use sand as the mineral component. Someone suggested using a regular light bulb instead of a grow-light. I'm going to try it with one plant, any suggestions as to the wattage?
Here is a photo of our very typical glass doors, so you can see what is inside gets sun only once a day and what is outside gets no relief from it, so I have to choose where a plant is going to stay the entire workday. The plants that do well in this house are philodendron, prayer plant, ponytail palm and succulents, all plants where the root leaves nothing to spare for gnats. Caladium, rex begonia, spider plant and ferns didn't last long. But these are all very common considering I grew a prize-winning avocado where I lived before and the house was an extension of my work as a greenhouse manager. So being reduced to a few "restaurant species" is a pain. The plants I would prefer to grow are beyond my abilities right now.

purple, you won't use indoor systemic and i certainly would and do. no kids, no pets though. Op does not state his preference, so i see no reason not to suggest what works for me.
it's a much milder formula then for outdoors.
AV people use marathon all the time - and it's also indoor systemic based on imidacloprin.
there's no way to really get rid of scale or mealies for example without systemic.
i lost a LOT of plants before i discovered indoor systemic specifically. now scale or mealies are not a factor - at least they don't KILL my plants any more, i can zap them fast.
OP seems to be desperate about gnats - it definitely WILL get rid of them fast. i don't know of any other solution that works as effectively. perhaps you do?
may be he knows about systemic, may be he does not.
and it is not really clear whether that's the only pest problem he's having or there are more.
anyways, in my opinion, it's def worth considering.

This post was edited by petrushka on Tue, Apr 15, 14 at 22:27

oh, so you were a greenhouse manager, so there's much less to explain :), so to speak.
i have all the plants you mentioned - caladiums and rex need very good light - sev hours of morning or evening sun is a must. but then again, most people don't do caladiums indoors, i actually do and for many years.
do you want them outside in pots or ground? this is a houseplant forum, so it's def inside?
even philo's need medium light to grow well.
unfortunately if you don't have the proper light your plant choice is quite limited.
as far as lighting - you really need to use fluorescent light fixtures. the bulb or two won't be enough, certainly not the incandescent. though some people use the chandelier lights - multi bulb, flip them up upside down and use them as directional with fluo bulbs. or a floor tree lamp with multi arms. saw some in citrus forum - they need good light when they bright them indoors.
there's a lot of good info on lighting/pests/nutes in citrus forum - avocado has similar reqs. you might want to browse or search there too.

what direction your windows face? that's critical to know, also where are you roughly - sun angle plays a role too.

I don't have problems with fungus gnats, so no need to experiment. They require certain conditions, and LOVE peat, both of which I avoid. IMO, that's easier than trying to constantly kill them - which sounds really annoying and expensive, from what people write about them.

I also don't have time to continue a discussion with someone who, instead of saying thank you for responding, would rudely ignore most of the responses and argue with some of them.

Petruska, you know I consider you a friend and well admire your plant collection, but completely reject the reasoning that because other people are doing it, it's perfectly safe, or that prophylactic chemical pest control is necessary. I would encourage people to investigate any chemicals they are considering bringing into their home and make their own decisions.

It also doesn't make sense to me to spend money fighting pests on a Coleus plant that costs less than $1. No rule against trying though, if one decides that's the best thing to do.

Good luck, Lenrely!

it's not about 'because other people are doing it, it's perfectly safe'. it's an option that OP can investigate based on his views/approach. that lots of people use. whereas you do not. it's a personal choice.
and i did not say it was perfectly safe either, by the way.
lets agree to disagree.
i am not adamantly arguing FOR or AGAINST it.
that would be the subject in itself in another thread.
but this is a public forum, purple. you have your opinions and i have mine.
tabacco is a poison, alcohol is a poison, most household chemicals are poisons, including bleach, boric acid, etc.
lots of plants are deadly poisonous, including many houseplants - that does not stop people from growing them. knowledge is key.
and sometimes it's necessary to 'choose lesser of 2 evils' - and that's an individual judgement.

This post was edited by petrushka on Wed, Apr 16, 14 at 11:58

i did not find op's response rude.
and well..., actually OP did thank all for response on apr 11.
you sound a bit off-handed though in the last post...

Thanks for letting me know! I apologize, not my usual luxury of time to read closely lately, and have deep passions about some things. Though the minute scale of chemical warfare regarding house plants is a mere blip on the radar, it concerns me enough to feel compelled to encourage folks to investigate, and not take decisions about it lightly - or fail to question the proven unreliable government entity which tells you it's safe. (Not to imply that you or anyone else here in particular has done so!)

I'm not upset with you or Lenrely. My "everbody's doing it" thing was addressing your, "AV people use marathon all the time." I don't mind agreeing to disagree at all, glad to have a more rounded discussion with 2+ sides. Your input is as valid as mine, it's what you believe, and I respect you for it.

"i did not find op's response rude." That's good. Intent/tone sadly fails to convey in writing, surely I've had problems with being misunderstood as well. Hopefully I'm the only one who failed to 'get it!'