My (few) experiences using hydrogen peroxide for molds and algae

I’m planning to write other pages about mold, and how to use hydrogen peroxide for molds. For example, how to clean walls and windows that have mold, using hydrogen peroxide to clean molds in carpets and clothing. Also some different kinds of mold, and how to prevent them.

But, first, I want to write about my own (few) experiences killing mold and algae with hydrogen peroxide. It seems a good starting point.

I've only had a very few occasions to use hydrogen peroxide for molds, yet I think my few experiences are instructive and useful. I’ve been using hydrogen peroxide for quite a few years, I just haven’t had much in the way of mold problems to try it out on….. .. which I think is good!


Cleaning algae out of a plastic water container

Several years ago, in an effort to drink more water, I got in the habit of using a ”sports bottle” at work. (This is a giant plastic bottle with a big straw. This way there is no trash from throwaway water bottles.) I would refill it with water, and used it every day. It always had water in it, I would just add more and keep drinking.

I don’t think it occurred to me that the bottle itself would get algae growing in it. But, for some reason, as is usually the case, one day I did look down into the container. Ug. Green. There was some green around the bottom of the container, just a bit on the plastic all around. Oh, dear. Not something I like to think of drinking out of! (Now, thinking about this, I think this is probably algae rather than mold.)

As it happened I had some 3% hydrogen peroxide at work. So, I emptied out the water and poured in the 3% peroxide, whatever I had – probably less than ½ cup. It was just what I had on hand. I clearly remember thinking that I was sure this would help. Because I knew that hydrogen peroxide is great stuff, I expected to see the green parts floating in the middle. I had faith! I left the water bottle in my office.

The next day, I looked in (expecting, as I just said, that the algae would be floating free in the middle, just a bunch of dots of green floating around.) But, there was no sign of green or slime at all! The hydrogen peroxide looked completely clear. I was impressed with this. Granted, it was not a lot of algae to clean up, but it seemed very elegant that it was completely gone.... just clear liquid.....

Of course, I dumped out the remaining peroxide, washed the bottle out, filled it with water, and went on using it.


A lemon tree that had a lot of black mold on the leaves and on the lemons

I’ve also used peroxide in gardening for years.

My meyer lemon tree is next to a fence, so parts of it are in a lot of shade, which may be part of why it developed black mold on many of the leaves. This developed slowly over at least a couple of years. The mold did seem to be worst on the side of the tree next to the fence. Maybe the tree needed to be pruned more, to let in more sun. I’m not sure. The mold also affected the lemons – some were covered with it. (They were still perfectly edible, they just needed to be washed off.)

I did think that spraying the tree with hydrogen peroxide would probably help, but, frankly, I thought it would take doing it several times, or using a stronger solution than what I could make (in my sprayer), or both.

As I noticed the mold was getting worse, however, I needed to do something. Of course, I started with what I had on hand easily: my garden sprayer, which I used to mix about 3 cups of 35% hydrogen peroxide into 20 gallons of water from the garden hose. (Note: this is about 4 times more concentrated than recommended for general purposes for watering a garden. The general recommendation would be about 3/4 cup of 35% hydrogen peroxide to 20 gallons of water. I was using about 3 cups of 35% hydrogen peroxide, thus 4 times the general watering recommendation, or twice as much as the extra-strength dilution for sick plants.) (For more information on dilutions, see the mixing charts for gardening, here...)

I sprayed the tree all over, repeatedly, with this solution. (I mean “repeatedly” on one day, not on several days.) I probably put the majority of that 20 gallons of water on the tree. I sprayed all over the tree, and especially over the moldy areas. (Some of the 20 gallons also went to other areas in the garden.)

To my great surprise, this one treatment has been enough to greatly reduce the mold. It is mostly gone, with only a small amount in a much smaller area than before. I find this quite remarkable. Even though I am very impressed with hydrogen peroxide, in general, for so many things, I still find it amazing that this concentration of peroxide could have such a big effect on chronic black mold!

What are my plans for the tree now? Well, I’m not worried at all about the mold anymore. I will be sure to spray the tree again with hydrogen peroxide from the garden sprayer, the next few times I use it. (I only generally do this 2 or 3 times a year.) If I get inspired about it, I might also hand-spray some 1% peroxide on to the moldy parts of the tree with one of the spray bottles that I usually use (with 3% peroxide) for house cleaning.


Using hydrogen peroxide for molds grown in juice

I had accidentally left a plastic cup with some juice in it, in my bedroom. I think it was pomegranate juice or some other unusual juice rather than grape juice, I’m not sure. And I’m not sure how long it was in my bedroom – a few days at least. Long enough to turn into a big pad of mold, really moldy and yucky. It looked big and spongy, and had lots of loose powdery mold on the top.

I honestly don’t remember if I poured 3% hydrogen peroxide on it, or if I used 35% peroxide. I remember dumping the big clump of mold into the kitchen sink, and I remember watching it shrivel up before my eyes. (Wow!) There was still a small moldy bit left – link a little pad of mold rather than a big spongy-looking thing. (I put it in the compost pail.)


Using hydrogen peroxide for molds

All of these experiences leave me thinking that hydrogen peroxide for molds can certainly be effective. If I should ever have moldy clothes or carpeting, I’ll see how hydrogen peroxide for molds works out with those. In the meantime, I just have these few experiences, along with things I’ve read about how to use hydrogen peroxide for molds.

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