Acid or alkaline?

michellescroggin(z6 western MA)May 22, 2006


First off, let me state I am NOT a chemist!

MANY years ago, I knew a woman who had the most beautiful (i.e. HEALTHY!) African violet plants I have ever seen. She swore it was because she added used coffee grounds to the soil and occasionally even watered them with a little diluted brewed coffee in order to keep their soil acidic, since violets like acidic soil.

About two years ago, I read an article online that stated that many houseplants will thrive if watered with a solution of hydrogen peroxide and water (4 oz hydrogen peroxide to 1 gallon water). My understanding is that it releases oxygen to the plant (hydrogen peroxide's molecular formula is H2O2, so it is bacially water - H2O - with an additional oxygen molecule!) that can enhance root development and also help treat root rot. I've been doing it since with all my plants (including my African violets and hoyas!).

Since H2O2 is an alkaline, it would seem that adding it to the water with which I water my hoyas and African violets would be counterproductive.

SO...there's my question: Do you think it is wise to water my violets with the H2O2? Do you think I should follow my old friend's example with my violets and add coffee grounds?

Any thoughts or suggestions would be appreciated!

:o) Michelle

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aes123(Z6 OH)

Let me begin by saying that I've been growing and reading about AVs for just over a year, so I may have some of this wrong.

I would do neither. My understanding is that AVs like neutral to very slightly acidic soil, so adding peroxide would be bad to begin with. Also, as delicate as AV roots are, I'd be afraid the peroxide would burn them, even if it were beneficial.

As for adding coffee grounds, I would think that as they decayed, they would release way too much nitrogen. Also, since the soil should stay roughly neutral, without a pH meter, it would be tough to tell how much to add, and when to stop.

For pH control I rely on having neutral media to start with, and repot twice a year, to prevent acid buildup resulting from the breakdown of the peat in my mix.

    Bookmark   May 22, 2006 at 10:47PM
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I have never tried either of these things with my plants. However, I am a chemist, so here's my $0.02.

I would be very careful adding hydrogen peroxide to plants. It is a strong oxidizing agent - this is why it can be used to bleach hair or as a disinfectant. It might treat root rot by killing bacteria in the soil, but at too high a concentration it could damage the roots.
Hydrogen peroxide spontanteously degrades to produce liquid water and oxygen gas.
2 H2O2 (l) ---> H2O (l) + O2 (g)
I don't know if plant roots can take up oxygen directly from the soil like this. Does anybody know?
Hydrogen peroxide also acts as a weak base (alkali), but at the concentration you mentioned, I don't think it will have very much effect on the pH of the soil. Commercial hydrogen peroxide is approximately a 3% solution - if you are diluting 4 oz to a gallon (128 oz), that makes a 3% solution of the original solution.
0.03 x 0.03 = 0.0009% hydrogen peroxide given to the plant. This small concentration is unlikely to harm your plants, and you are clearly doing something right if they are healthy.

Why not do an experiment? Get 3 cheap violets from the grocery store, keep them under the same conditions, and test these things out. Give one only water as a control, give one hydrogen peroxide, and the other one coffee grounds. Then you can see if they grow differently. I'm sure the results would be interesting.
Good luck!


    Bookmark   May 23, 2006 at 12:06AM
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Whoops! I just read my last post and realized I made a typo. I should have said
.03 x .03 = 0.0009 = 0.09%
Still a small concentration, but I wanted to correct the error.

    Bookmark   May 23, 2006 at 1:36AM
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michellescroggin(z6 western MA)

Hello Rachel!

Thank you so much for your reply!

I'd actually thought of doing the same thing you suggested - "experimenting" with three violets. I'm afraid ALL of my violets are the cheap Home Depot kind (I'm really more of a hoya collector), and I have several from which I have made new plants from maybe I should start my experiment this summer!

Thanks so much for your input!

:o) Michelle

    Bookmark   May 23, 2006 at 8:55AM
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korina(9b, Sunset 17)

Michelle, your friend may well have been using actual garden loam to keep her plants in; it was common practice for a long time. This would affect *everything*. Today's soilless mixes are sterile, so I don't think coffee grounds would be able to break down properly. And of course the acidity would be extremly variable.

Just a thought.


    Bookmark   May 23, 2006 at 12:01PM
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irina_co(z5 CO)

I sometimes use peroxide in the water for AVs instead of Physan to keep algae at bay. The second plus - looks like it suppresses fungus gnats - but I use a table spoon per gallon and it seems beneficial for the violets - so you can do it.
The modern violet soil has a lot of peat in it - and it is acidic and gets more acidic with time - so coffee grounds would be too much. I use coffee grounds on my outside roses - our soil is alkaline - so it adds acidity, they break and add nitrogen to the soil and they could be used as mulch for outside plants. So - get your bucket and bring home all the coffee grounds from work. If you add water to the bucket - you could fish the paper filters out easily. All outside plants will be happy to get cafeinated.


    Bookmark   May 23, 2006 at 3:30PM
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korina(9b, Sunset 17)

Oo, don't forget, Christmas cactus like a little coffee now & then too!

Korina, tea fiend

    Bookmark   May 24, 2006 at 2:59PM
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minibot(z9bNorCA Sz16)

I've also read to use epsom salts to cut the acidity once in a while if you are using any acid in your water/feeding. So all acid does tend to produce tight leaves...hence tighter crowns on plants in acidic soil, especially peat. I've noticed the color change, but also my centers seem a little squished and the blooms seem tight from the acid. I'm going to water with an epsom water mix next to try to lower the pH at least once a month.

Then again, I may just switch to Eleanors food only, and see how they do on that for a while. My plants want to struggle with the coir mix for some reason. It seems to dry out easily, but heck at least it rewets faster than a brick of peat !


    Bookmark   May 24, 2006 at 5:34PM
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Hapslappy(Mi z5b)

hmm, I read awhile back about peroxide being used to kill off bad bacteria in the soil. Well, it also said that although it may do that, it will also kill any bacteria that may be beneficial to the plant. (Although I don't know the details, or even if what I'm saying is relevant to the topic) Anyway, I don't add anything & mine do just fine. :-D Shannon

    Bookmark   May 26, 2006 at 3:51PM
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