Houseplants forum: Bought 3 yuccas in a pot.1 is thriving, 2 are dying. Overwatering or gnats?Both?

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venexiano
Jun 22, 2020 10:27 AM CST
Hi,

I bought 3 yuccas (a big, a medium-sized, and a small one) at Home Depot (see first picture). They were in the same pot. I left the big and small in the original 13" pot (adding a little bit of potting soil bought at home depot). And moved the medium to a 10" pot (adding potting soil, maybe half of the total final soil). First 3 weeks I messed up since I didnt put them next to a window. Then after reading online, I have put them right in front of a window. North window for the big pot, south for small. North is brighter, but no direct sunlight in either. The big yucca after an initial discomfort seems to fair very well! The other two are in very bad conditions, I wonder if they are dead or if I can still recover them (see pictures). I watered once per week. There are gnats everywhere in my house since I bought the plants 2 months ago. Never had plants before in my house, and never had a single gnat. So I might have overwatered, or might be the gnats. Or both since gnats like water. They bite like crazy, so I guess they are not fruit or fungus gnats. Yesterday (the pictures of dying yuccas are from 2 days ago) after reading online about the use of 3% Hydrogen Peroxide for root rot and gnats, I sprayed a mix of 1 spoon of 3% peroxide and a cup of water on the leaves, and 1/1 ratio of 3% Peroxide and water in the soil. I have decided to move watering to once every 2 weeks, it has been 8 days since I watered. So in 6 days I will water them with the 1/1 3% Peroxide solution. I chose the proportions based on this youtube video ("5 Benefits of Hydrogen Peroxide on Plants and Garden", I can't post links). I added gnat stickers to the 2 pots, plus 2 electric zapper next to them, I killed like 200 gnats over 2 days. Am I going in the right direction? Should I cut the hanging branches? They seem rotten. If I see no improvement in 4 weeks after 2 watering cycles with peroxide, I am considering trying to also remove the 2 dying plants , spray the 1/1 peroxide solution directly on the roots and repot them in the same pot with same soil.
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Name: Will Creed
NYC
Prof. plant consultant & educator
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WillC
Jun 22, 2020 2:15 PM CST
The roots of plants are quite fragile and easily damaged when plants are separated and repotted. That is why yours are struggling now.

The gnats or whatever they are were introduced with the contaminated soil that you used. Hydrogen peroxide is not an effective treatment, but given the extent of the and infestation, I'm not sure there is an effective treatment for them. Letting the soil dry out as much as possible will help some.

Yuccas do best in front of very sunny windows.

Stems that are soft and unable to support themselves are already beyond recovery and can be cut off and discarded.

For future reference, the next time you want more than one plant, buy more than one plant. Trying to separate plants grown together by the nursery risks losing all of them.
Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care

venexiano
Jun 23, 2020 9:53 AM CST
Thank you. The soil was brand new soil bought at home depot. It was not contaminated. Are you saying that the Yucca is gonna dye 100% sure or is already dead? Is there really no hope or anything to try? Did you mean that peroxide is not a good treatment for gnats or did you mean for root rot? Could you please elaborate on it? I see that many well-known websites speak highly of Peroxide, such as gardeningknowhow (cant post link, google gardeningknowhow Hydrogen Peroxide)
Name: Will Creed
NYC
Prof. plant consultant & educator
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WillC
Jun 23, 2020 1:28 PM CST
Because potting soil is new and in an unopened package does not mean it is pest-free. Potting soils are completely unregulated and fungus gnats are common in many packaged potting mixes, especially those with bark, compost, soil and other organic materials.

Peroxide seems to be a popularly recommended online cure for practically everything. In my experience, it is not effective in treating fungus gnats. Apparently it hasn' helped you with yours either.

The roots of your plants are likely suffering primarily from the physical damage done during your root surgery and may also be suffocating from lack of oxygen subsequently. It is not a bacterial or fungus disease that can be treated with peroxide.

Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care

venexiano
Jun 23, 2020 5:39 PM CST
Well as I wrote above, I have just sprayed some peroxide 2 days ago, it seems like there are way fewer gnats around. And I did not water with Peroxide yet, I will do it when the soil gets pretty dry, probably in 6-10 days. I want some oxygen to get to the root first, I do not wanna overflow them again. It might not work, but I think it is worth trying. I agree with what you said, that "plants are likely suffering primarily from the physical damage done during your root surgery and may also be suffocating from lack of oxygen subsequently". 100% true, that is the spot-on diagnosis. But I do not agree with this "It is not a bacterial or fungus disease that can be treated with peroxide." Or better I do not agree with the first part. It might be true that peroxide might not work, but it is also true that root rot is due to anaerobic bacterias consuming the plant in low oxygen conditions. And an extra oxygen molecule of Peroxide (H202) is released when poured into the soil which helps with oxygenation of the soil and death of anaerobic bacterias and slowing (possibly reversing?) root rot. Again, you might be right that it might not be enough or might be too late, but the rationale and science behind it cannot be ignored. I hope you accept this as a constructive discussion, if I said something wrong please feel free to correct me.

Here are some peer-reviewed scientific publications mentioning bacteria and fungus as the cause of root rot:

M. C. Drew and J. M. Lynch, SOIL ANAEROBIOSIS, MICROORGANISMS, AND ROOT FUNCTION, 1980, Ann. Rev. PhytopathoL 1980. 18:37-66.
Bodah, Root Rot Diseases in Plants: A Review of Common Causal Agents and Management Strategies, Agri Res & Tech: Open Access J 5(3): ARTOAJ.MS.ID.555661 (2017)

Here a recent publication highlighting the important role of Peroxide in plant biology:

Cerny et al., Hydrogen Peroxide: Its Role in Plant Biology and Crosstalk with Signalling Networks, Int. J. Mol. Sci., 19(9), 2812, 2018
Name: Will Creed
NYC
Prof. plant consultant & educator
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WillC
Jun 24, 2020 7:43 AM CST
For sure, roots can die because of fungal and bacterial issues. However, roots can also die from physical damage and from suffocation or lack of oxygen. In those instances, no bacteria or fungi are involved. Dead roots look like dead roots regardless of the cause and the cause is often "assumed" to be root rot caused by an infection.

Thanks for sharing the citations. The first article you cited refers to plants grown in outdoor environments. Potted plants grown for indoor use are typically grown in sterile potting mixes so that bacterial and fungal problems are relatively rare. Outside grown plants are much more prone to a variety of diseases.

I tried to wade through the article on peroxide. It is highly technical, but I found nothing in it that suggest that it is an effective treatment for either gnat larvae or potted plants that have been overwatered or otherwise damaged. I understand the logic of adding extra oxygen to improve an anaerobic condition, but when the source of that extra oxygen is mostly water it seems counter-productive to allowing the goal of allowing the soil to dry out.

Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care

venexiano
Jul 13, 2020 6:04 PM CST
Hi,
I just wanted to update after about 1 month and a half. I did 2 treatments with Peroxide, every 2 weeks I saw a very strong reduction in gnats, but unfortunately, there are still some. I applied to all my 10 indoor pots, not only the 2 yuccas. I would say 80% reduction, but they were a lot. I am not sure if I should keep going with the Peroxide, I am afraid in the long run it might arm my plants. Is there any insecticide I can pour in the soil that is safe the plats and would finish up the gnats? Online I see people suggesting sprays based on pyrethrin. What are your thoughts?
Name: Baja
Baja California (Zone 11b)
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Baja_Costero
Jul 13, 2020 6:19 PM CST
Those plants need to "see" the sun for hours a day, year round. This is not really optional. It will benefit the plant and help with the gnats, which may be a great annoyance but do not threaten the plant.

Put sticky flypaper in there near soil level and you will see a great reduction in flying adult gnats. I would quit using peroxide. More light and less water would be more helpful. Try drenching the soil with insecticidal soap (i use Safer brand) but you have to treat all your plants (no safe haven) and combine this with flypaper.
Name: Lin Vosbury
Sebastian, Florida (Zone 10a)

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plantladylin
Jul 13, 2020 6:27 PM CST
I agree, your Spineless Yucca (Yucca gigantea) needs less water and much more light! Yucca is a fairly drought tolerant plant and the soil should be allowed to dry sufficiently between waterings. Fungus gnats can be present in some bagged potting soils and are usually present in soil that stays overly wet. Once you get them under control, allow the soil to dry sufficiently before adding more water.
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venexiano
Jul 14, 2020 5:14 PM CST
Thank you, I forgot to mention I have sticky flypaper in each of the two yuccas since 6 weeks. They have tens if not hundreds of gnats attached to them. I will put some on the other plants too I guess. Is this the Safer Brand you mentioned? https://www.amazon.com/dp/B00192AO90/

venexiano
Jul 14, 2020 5:21 PM CST
Reviews are mixed....some people say it does not do anything for gnats, some people say it works...These are biting gnats, they bite like crazy...not sure if it helps
Name: Baja
Baja California (Zone 11b)
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Baja_Costero
Jul 14, 2020 5:24 PM CST
Then they are not fungus gnats (which do not bite). That is the product that I use. It works great on fungus gnats when combined with sticky flypaper. You have to completely saturate the soil (so water carefully and return in a few minutes to water some more), you have to treat all plants in a given area (no safe refuge for the gnats), and you have to be aware of the potential for new gnats to come in from nearby plants, new plants, or the soil that you use.
[Last edited by Baja_Costero - Jul 14, 2020 5:26 PM (+)]
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venexiano
Jul 14, 2020 5:29 PM CST
Ok thanks. Here: https://homeguides.sfgate.com/... they say " Fungus gnats often can be controlled without the use of pesticides. If indoor potted plants are affected by fungus gnats, then remove the top 2 inches of soil around each plant. Discard the soil -- along with the soil-dwelling larvae -- in a sealed plastic bag, and replace the pots' removed soil with sand. The sand makes the soil inhospitable to female fungus gnats looking for organic material in which to lay eggs. Allow the soil under the sand to dry out before each watering." .
What about doing that as well? Is there a way I can use relatively fine white gravel instead cause it looks better? Or would gnats pass through the gravel grains? Any idea on the grain size I could use for gravel to still prevent gnats from enter the soil?

venexiano
Jul 14, 2020 5:43 PM CST
And Baja, you mean that I need to saturate the soil with water and then pour the liquid insecticidal soap, or that I need to saturate the soil with liquid soap directly?

venexiano
Jul 14, 2020 5:50 PM CST
The comments on these reviews all say that this kills gnats, and it looks cute: https://www.lowes.com/pd/AKASH...
Name: Baja
Baja California (Zone 11b)
Be a superhero and wear a mask
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Baja_Costero
Jul 14, 2020 5:54 PM CST
The insecticidal soap product you selected is a 50x concentrate, meaning you have to dilute it 50-fold in water before use. Which works out to 40ml = 2.7 tbsp per 2 liters. Wait until it's time to water (ie. when the soil is drying out at the bottom), and then water with the diluted soapy water instead of regular water (making sure it comes out the bottom, and returning at least once to water some more). Maybe refresh the flypaper at that point so that you have maximum effect, in case the existing one is kind of old and has lots of bugs stuck to it.

Also make sure you consider possible sources (like new soil or new plants, or your neighbor's garden), maybe change the soil you have been using if that's an issue, because once the soap washes out, the soil becomes habitable for gnat larvae again. Also consider investigating what the biting bugs are, because it sounds like you have 2 problems and only one of them is fungus gnats. Any chance of a photo showing the bugs you've trapped on the flypaper?

Improving the light and watching how often you water will also have beneficial long term effects.
[Last edited by Baja_Costero - Jul 14, 2020 5:57 PM (+)]
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venexiano
Jul 15, 2020 5:01 PM CST
Here is the picture. Note that I always said they are biting gnats, also in my first post. I never said they are fruit knats. They bite very aggressively...if one gets into my room (no plants here) it bites and bites me. They definitely are on the plants cause:
1) They showed up when I bought the plants
2) When I waive my hand on the top of the soil 3-4 start to fly or walk around

You did not say anything about the sand. Should I go for it?

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Name: Baja
Baja California (Zone 11b)
Be a superhero and wear a mask
Cactus and Succulents Seed Starter Foliage Fan Xeriscape Container Gardener Hummingbirder
Native Plants and Wildflowers Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator
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Baja_Costero
Jul 15, 2020 5:07 PM CST
All the advice I have given relates to fungus gnats. I have nothing to say about the biting kind, no experience there.

The bugs in the picture look like fungus gnats to me, but I'm no kind of insectologist.

The sand might work for you but I would be careful not to over apply aggregate as a top dressing. The danger is you can create a moist environment in the soil without the chance of evaporation, which will foster the growth of all kinds of other organisms that are not good for the plant, potentially entombing it. As long as the top dressing does not interfere with evaporation, go for it.
[Last edited by Baja_Costero - Jul 15, 2020 5:09 PM (+)]
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Texas (Zone 8b)
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Galathiel
Jul 18, 2020 12:19 PM CST
I've found that Mosquito Bits worked really well for me when I was a new(ish) plant person and loved my plants a little too much (overwatered). Now that I water when my plants have dried at depth, I no longer have issues with them. You can also soak the mosquito bits in your watering water and use it that way. That's what I preferred to do: drop some bits in my water bottle, fill it up, shake it, and then let it set over night before watering. I also preferred to mix my bits into the soil instead of just sprinkling on top.

https://www.amazon.com/dp/B0001LE1VC/

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