Using hot water on plants?

smithjm(z9 FL)September 10, 2006

I have a big problem with fungus gnats and was doing a search here. Alot of you said to let the soil dry out. I've done that and it doesn't work. It's especially hard to do that when you have plants that can't go dry, like calatheas to name a few. So then finally someone said about using hot water. Just plain hot water! just enough to cover the soil, not drench it. I haven't tried this yet, I guess i'm afraid to kill my plant. The person assured that it will kill the larvae but not damage your plant. Has anyone tried this method?

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ines_99

I have but am afraid to go too hot, so it hasn't worked. Buy the pond tablets at your local garden center, called mosquito dunks. Soak one in water overnight and then use to water your plants a few times. Safely kills all the larvae.

    Bookmark   September 10, 2006 at 1:00PM
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birdsnblooms

Smith, how hot is hot? If you're talking overly hot, I wouldn't do it..You'll burn the roots. Smith, I allow my calatheas to dry out between waterings. Not so much that the leaves brown, but just enough fungus gnats don't make a home of soil.
One thing you can try is using a fan to circulate the air..this should help a lot. Especially if the room is humid. (or dry)
There are systemics, but I don't use chemicals on plants other than fertilizers. This is entirely up to you though..some ppl use chemicals and rid bugs..but even if you do, and keep soil wet, they're just going to reappear. I'd keep the soil dry and get a fan..Toni

    Bookmark   September 10, 2006 at 3:55PM
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highalttransplant(z 5 Western CO)

I tried this a couple of weeks ago for a fungus gnat problem, and the plants handled it fine. The problem with this method is it only kills the larvae. Either new ones have wandered in since then, or some of the adults lived long enough to lay another bunch of eggs. So I would say if you did this on a regular basis you could definitely decrease, but not completely eliminate the population.

    Bookmark   September 10, 2006 at 3:56PM
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smithjm(z9 FL)

In my apt, it's as hot as the water is allowed to get. It won't burn you but it's hot enough you can't leave your hand under the faucet for more than 20 secs or so.

    Bookmark   September 10, 2006 at 4:37PM
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birdsnblooms

High, how did you know what temp (hot water) to use? I'd think this would harm the roots as freezing water would.

    Bookmark   September 10, 2006 at 4:38PM
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pirate_girl(Zone7 NYC)

Hi Smith,

Since I'm one of those who suggested you let the mix dry out somewhat, let me ask how long you did do that for, after which you feel it doesn't work (kinda needs to be more than a day or 2)?

Not to sound like a broken record, but it's yr. watering that's the problem here, you really need to get a handle on this underlying problem as I feel the gnats are just a symptom & you'll like have other problems from this after the bugs are gone (mildew, root rot, etc.)

Just a suggestion (since I see elsewhere you're interested in lots of diff. plants). It might be worthwhile to stop acquiring new plants, 'til you get a handle on this, lest you lose the addt'l plants you're planning to buy. Even if money isn't the issue, it might be quite frustrating & disheartening for you. Learning proper culture & taking the time to put that into practice takes time & patience, something that's often not mentioned in learning/growing nice, healthy plants.

My 5 cents.

    Bookmark   September 10, 2006 at 4:50PM
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highalttransplant(z 5 Western CO)

I hate to sound defensive, but in my case I'm pretty sure my watering is NOT the problem. I live at a high altitude, where there almost NO humidity, and I let the soil become completely dry, I push my index finger to the second knuckle and feel NO moisture. I've even let the plant start to wilt slightly before watering again, yet I still have fungus gnats.

Toni - I followed the poster's suggestion of tap water that was hot enough that you would only want to hold your hand under for 15 - 20 seconds. Not scientific, I know, and I admit I was nervous about doing it, but my plants did not seem to be bothered by it at all.

    Bookmark   September 10, 2006 at 5:05PM
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karen715(z5 IL)

I would like to weigh in as someone who also strongly disagrees that overwatering is always the culprit in fungus gnat infestations. I tend to let my plants go a little too long between waterings in general(my bad, but fortunately, I do not grow any true moisture lovers). It has been a very long time since I overwatered anything. Nothing in my house stays very moist very long. Yet I have had trouble with gnats on and off. The problem seems to be that peat-based potting mix occasionally harbors the eggs or larvae. For example, the mix included with Amaryllis kits is always pure peat. In my experience, it always, always, always harbors gnats. Even those compressed peat discs that come with the new kits has them. Though I normally throw the bagged Amaryllis mix out, I tried out one of the discs that came with a gift bulb last winter, and this is what reintroduced gnats to my home.

My recommendation is to get a BT-based control. (Knock-out Gnats from gardensalive.com is one brand, Gnatrol, I think, is another.) These are non-toxic and environmentally friendly, even to the degree that our resident chemical-hater, Rhizo, approves of them. I would also use yellow sticky traps for the adult gnats, to prevent the life-cycle from continuing.

I never water my plants with anything but room temperature water, and would be hesistant to do otherwise.

    Bookmark   September 10, 2006 at 6:47PM
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birdsnblooms

Fungus gnats are a pain. They dote on dry or humid but stuffy rooms. This is why I suggest using a fan..even in winter I run fans on low..this also regulates heat to distribute it evenly. I've seen fg's in places like HD.
The only problems I have w/fg's are on seedlings. Karen, maybe you're right about the peat, cause I sow seeds in peat pellets/pots. But once seedlings are old enough to be repotted in a regular pot, I no longer have this problem.
But, there were a few times in winter I'd see the little buggers running through soil..and this was in rooms that 1. didn't have a humidifer and 2 didn't have a fan running. I'm still stuck on the notion that too much water is at least one of the reasons fg's appear. I keep seedlings quite moist. Toni

    Bookmark   September 10, 2006 at 8:10PM
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smithjm(z9 FL)

Karen, believe me, my watering is not the problem. Those things just hang around here even if the plants are bone dry. I mean, I live in Florida!! is so humid here, I go outside and my glasses fog up!! so maybe the problem is where I live. The only plants that I have, that require constant moist soil, are calatheas and fittonias. And even those I let dryout slightly. Most of my plants are the kinds you can let dryout almost completley if not all. I have so many plants plus 3 kids! I don't have the time to be watering all the time. So I always tend to buy plants that can take a little neglect. In my years caring for plants I can count in one hand the ones i've lost from overwatering. We have so many little creatures in this world, I really don't feel bad or blame my self (other than the times i've overwatered) when a plant dies because of some kind of insect. I mean they have to feed, and if it's not your plant, its another. Regardless, you are not responsible for what insects do, you cannot control them or the weather. They're all around us, even if you treat your plant, eventually they'll come back or you'll have a brand new problem you have to deal with. I wish all of us can have plants and not have to worry about insects,overwatering, weather etc... But that's impossible. I think all of us have had problems with one thing or another with our plants. They're no such thing as a perfect plant that lasts forever with no problems what so ever. If it was like that, than what on earth would we talk about in this forum? It be pretty boring! Who wants to read all the time about people bragging how perfect they're plants are and how they've never had to worry about bugs. Bottom line: Trial and error is what makes all of us better gardners.

    Bookmark   September 11, 2006 at 8:12AM
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smithjm(z9 FL)

That post was meant for Pirate girl not Karen.

    Bookmark   September 11, 2006 at 8:17AM
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rhizo_1 (North AL) zone 7

There's no way that hot water would kill the eggs, which is the step that has not been mentioned here. It takes a few watering cycles (with the Gnatrol or other Bt inoculant) to eliminate the population, but I assure you, Bt will do the job. It is not a chemical.

Peat based potting soils, especially those that are MOSTLY peat (thus finely textured), are the preferred haven of fungus gnats. Over-watering acerbates the population but you can still be 'bugged' by them as long as you use one of these mixes.

My recommendation to anyone who always seems to be harboring a small infestation of these annoying little creatures, is to purchase Gnatrol or some mosquito dunks and take care of the problem in the most efficient manner possible.

Systemics are absolutely not the way to take care of these pests, and I'm sorry to see that mentioned. Even contact chemicals are not required. Bt (Bacillus thuringiensis var. israelensis) is a naturally-occurring bacterium inoculant that kills the larvae of mosquitoes, flies, and gnats. It is non harmful to any other organism other than the specific targets of that bacterium. Gnatrol is probably the easiest way to apply it to indoor plants, though I know that several people (here in the GW) soak ordinary mosquito dunks and use that water for their plants.

Food/horticultural grade diomateous earth would be another helpful product to use.

    Bookmark   September 11, 2006 at 8:28AM
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karen715(z5 IL)

It works out well, smithjm. As it happens, Pirate Girl's name is also Karen :-)

    Bookmark   September 11, 2006 at 10:01AM
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pirate_girl(Zone7 NYC)

Well Smith & everybody else, I'm not trying to raise hackles here, if so, I DO apologize.

My plants & I are far from perfect, it's just that I don't often have insects (there are other problems instead). My bug experience is largely w/ my evil nemesis Mealies who can ravage a Hoya collection quite quickly. So I used Marathon once, in '02 & that was it. My only other bug experience are the infrequent fgs I seem to get from (1) leaving overripe bananas on my counter; & (2) growing Mangos from seed. I've concluded that perhaps Mango pits naturally harbor fg (the way figs can harbor wasps) as I seem to get them once the plant's abt 3-5" long (so no more Mango experiments for me, even tho' they're lots of fun, young plants goes thru amazing color changes that I love to watch: from apriocot to burgundy, to apple green & finally to regular dark green).

Like others I'm sure, I'm very cautious abt adding new plants to the collection, esp. from sources w/ which I'm not familiar. Importantly for me, I rarely use peat, so maybe that's why I don't often have this problem, tho' once in a blue moon I'll use a disk of peat to start something like a Clivia seed or a Coleus cutting.

Also, as a smoker, I ALWAYS leave my windows open 1-2", even in dead of winter, just 'cause I can't stand stagnant air. I figure the plants would hate that even more than I, so at a minimum there's always a bit of fresh air moving around my place & I usually run one big fan, Spring thru Fall (esp. now that I've just entered the world of Hot Flashes, ugh)

Yes Smith, Karen715 has it right, my name IS also Karen. We are the resident Karens (along w/ Karen MN, who tends to be mostly at Hoyas). That why if I sign, I usually sign

(PG) Karen

    Bookmark   September 11, 2006 at 11:01AM
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shiver

Just thought I'd throw in my two cents, as I sometimes have problems with these little buggers---especially in plants that have to remain very moist, like my juncus (a bog plant). I have tried hot water (just under the boiling point), and it did not kill the gnats or harm the plants. It did...well, nothing! I have used "gnatrol" with *great* success and love it. Still, the fungus gnats always seem to return to those plants needing wet soil, so I'm thinking of getting rid of those particular plants. I guess I'm just sick of those pesky buggers flying up my nose all day!

    Bookmark   September 11, 2006 at 11:05AM
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rhizo_1 (North AL) zone 7

I thought your advice was excellent, Pirate Girl. EVERY one's was! ;-)

By the way, PG,Do you think your other gnat problems might be fruit flies, rather than fungus gnats? Mentioning the ripe bananas and mango pits makes me wonder.

    Bookmark   September 11, 2006 at 1:11PM
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pirate_girl(Zone7 NYC)

Hi Rhizo,

Yes, actually I think you're right & they likely were fruit flies, not fgs. Either way, they are most unwelcome, nasty up the nose & altogether need to leave.

But I take your point, & now if I feel I must save overripe bananas (for baking, etc.), they go into the fridge or the freezer for future use. Working to make my environment less inviting to any & all little buggers!

    Bookmark   September 11, 2006 at 2:02PM
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highalttransplant(z 5 Western CO)

I think they probably ARE coming from the potting soil. I just recently bought a huge bag of it, so the timing certainly fits. What can I use instead of this? Can I just use the rest of the potting soil on my perennials outside? I still have a ton of it left.

    Bookmark   September 11, 2006 at 2:57PM
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rhizo_1 (North AL) zone 7

It's common for batches of peat based potting medium to become contaminated with fungus gnat larvae at the place of origin. If you prefer to dispose of it, rather than treating with Gnatrol for the rest of your days (lol), potting medium makes a good amendment in the garden. Those fungus gnats won't make it in your climate, that's for SURE!

    Bookmark   September 11, 2006 at 4:31PM
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smithjm(z9 FL)

I guess I may have to purchase this Gnatrol everyone's talking about. I've also read alot about mosquito dunks? I've never used them but did check for prices and the mosquito dunks are cheaper. Do they really work? it doesn't say anything about gnats on the bottle.

    Bookmark   September 11, 2006 at 5:02PM
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rhizo_1 (North AL) zone 7

Yes, it works. Mosquito dunks shouldn't come in a bottle. But anyway....you need to become a LABEL READER. Here's what you are looking for: ACTIVE INGREDIENT Bacillus thuringiensis var. israelensis.

That is the bacterium inoculant that kills the larvae of mosquitoes, flies of many kinds, gnats of many kinds. Period.

The problem with using the dunks is that there will be no accurate directions of how much water to use when preparing it for use for fungus gnats. That is one of the BEST reasons why using the product that is made expressly for this use might be best.

If you post a NEW thread pertaining to the question about mosquito dunks and fungus gnats, you will get some assistance on this issue. It's come up a few jillion times in the past, lol.

    Bookmark   September 11, 2006 at 10:57PM
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highalttransplant(z 5 Western CO)

rhizo - So if I don't want the gnats to come back after I use the Gnatrol, what do I plant my houseplants in, instead of the potting soil?

    Bookmark   September 11, 2006 at 11:06PM
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rhizo_1 (North AL) zone 7

If you use the Gnatrol through several watering cycles (or whatever the directions say), you shouldn't have any more problems. The pesky adult gnats lay their eggs in the potting medium. After a few days, they hatch out into those icky larvae. After a few more days, the larvae pupate and turn into more ADULTS! So, keep after larvae until all of the eggs have hatched , and you don't see any more adults flying around.

Make sure you watch your watering practices, increase air circulation, and change the brand of potting soil next time around.

BTW, if you'd add a bunch of perlite, bark fines, and other coarse materials to your existing potting mix, the fungus gnats would HATE you!

    Bookmark   September 11, 2006 at 11:51PM
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notanatural(z6 NY)

This is interesting coz a friend of mine is having major problems with gnats (or at least thats what I think it is- I have only heard her problems- never seen it). She says she has millions of tiny insects crawling in the pot. She kept marvelling at my plants when she was over here and I told her the only special thing I do is use neem oil so now she's gone off to get some.

I've never really had that problem at home. I saw a few of them after I brought back my plants from work (kept them there while I was away on holiday in the summer) but they've all gone now.

I think the air circulation must be quite a factor- I don't leave the windows open all day and night in the winter but as a smoker, I definitely like to air out the apt whenever the temp is warm enough. In the summer, windows are always open.

Our humidifier doesn't really work and the air is always very dry in winter- but it's hot so I can have a fan going on low. I think that's quite key as well.

I guess too much moisture in the soil encourages them but my calatheas are always moist and there's been no problems with them- and they're always kept near the heater in winter. So who knows why some have gnat problems and some don't.

I'm a huge huge fan of neem oil- and I regularly mist my plants with that (more in the winter than summer)- so perhaps that helps prevent insects of all kinds?

But I'm definitely going to tell her about the air circulation now- I didn't think of that before! I hate stagnant air myself but I didn't realize I was doing my plants a favour as well.

    Bookmark   September 13, 2006 at 9:36AM
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pirate_girl(Zone7 NYC)

Hi Nota,

Haven't seen ya around in a while. Yes, air circulation is a big & important factor. Check any commercial greenhouse you may visit (or those of wealthier hobbiests (?), they always have at least a couple of fans on. The plants really like (& I suspect need it) & it's a known factor in insect control.

    Bookmark   September 13, 2006 at 11:09AM
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gw:plant_babies

I live in a very low humidity desert environment. I have a lot of gnats -- my torchier lamp gets full of them!

I run high-end ceiling fans, and they don't appear to affect the gnat population.

I probably have 200 plants in my house, so tackling my gnat problem will be some chore.

I grow a lot of plants in water, so maybe this is where they drink.

I can see them running around on the soil even in the most dry plants.

I can't believe someone else has the 'gnat up the nose' problem too! LOL :)

pb

    Bookmark   September 13, 2006 at 1:52PM
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rhizo_1 (North AL) zone 7

Tackling a fungus gnat problem like yours should be no more difficult than attending to your routine watering, which is how you will be applying the Gnatrol (or mosquito dunk dilution).

Fans assist in helping with fungus gnat populations because they help speed up the soil evaporation process. Good air circulation is key in disease prevention, as well, which is the primary reason why greenhouses run circulating fans 24/7. Excess humidity is a problem in such environments, and fans help prevent moisture from collecting on leaf surfaces.

    Bookmark   September 13, 2006 at 2:30PM
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birdsnblooms

Pb, sounds like you have a real problem. 200 plants are quite a bit to deal with. What are you planning on doing? Repotting is an option, but it'd be a lot of work for sure. I wish you luck, Toni

    Bookmark   September 13, 2006 at 2:39PM
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notanatural(z6 NY)

Hi PG- I've been here- now and then, I read ofte, just having been posting very much.

I got a bunch of new plants few weeks ago- busy nurturing them.

The weather is changing here- and my hibs are NOT liking it.

Anyway, back to the gnats- what would you do if you had a very serious problem with gnats? I told my friend to repot- but she said it was much too big for her to do it now. Apparently it had just been repotted a few months ago in a gigantic pot (not sure how big or even what the plant is).

You think she should use some of the products mentioned here? I'm not a big fan of chemicals either but if there is an absolute serious problem I have no inhibitions taking out the big guns. Luckily all I've had to use is fungus and insect spray on a couple of my plants a few times. It worked and the plants are still looking and doing great.

    Bookmark   September 14, 2006 at 8:46AM
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smithjm(z9 FL)

I would treat the problem, wether it's small or not. If you repot they're just gonna show up again. It's better to use something to treat and prevent. I've tried repotting and keeping the soil dry and it does not work, atleast for me...

    Bookmark   September 14, 2006 at 10:21AM
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rhizo_1 (North AL) zone 7

If you have been following this post, notanatural, then you will see that Gnatrol OR any other product with the same Bt-i spore inoculant works exceedlingly well for fungus gnats. You should also know that it is not a chemical, per se, or a toxin (to anything but the larvae of certain insects....one of which is the fungus gnat.)

Just to make sure that you understand that the use of Gnatrol (Bt-i) is organic and natural, I will attach a link that will explain it to you. No need for chemical soups, drenches, sprays, etc. Bt is applied right along with the water during routine maintenance, no special treatments required.

Here is a link that might be useful: Understand?

    Bookmark   September 14, 2006 at 11:33AM
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pirate_girl(Zone7 NYC)

Rhizo,

Can I just say, "You Rock"!

    Bookmark   September 14, 2006 at 12:01PM
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notanatural(z6 NY)

Thanks rhizo- I had only been vaguely following the post- I admit to selective reading. Too much detailed info sometimes just goes over my head and besides, this matter didn't really directly pertain to me. But now I have, and now I 'get it', lol. Thanks!

    Bookmark   September 19, 2006 at 8:50AM
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rhizo_1 (North AL) zone 7

;-) I had a suspicion that you weren't paying attention, notnatural! lolololol

Thanks, pirate girl!

    Bookmark   September 19, 2006 at 10:21AM
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preciousjoy

Plants that don't like cold wet feet enjoy being watered with warm/hot water. Great for soaking seeds, watering seedlings and older plants for healthy growth.
I don't feel it will get rid of all cycles of gnats which begining cause can be from over watering but once you get them can be hard to get rid of.
GardensAlive sells a good product to rid all cycles of gnats.

    Bookmark   August 26, 2008 at 6:38AM
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