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Hydrogen Peroxide Uses for Gardeners


By darren8


Some years ago I had the space & finances to grow all sorts of plants indoors under lights & I routinely used hydrogen peroxide to clean & oxygenate the soil in pots. My circumstances changed & I forgot about using HP (H2O2). Recently however I remembered it can be very useful for all sorts of things in the garden, with houseplants & in greenhouses.
There are some people that claim it’s miraculous but I think it’s just chemistry. So I thought I’d document my usage: i.e. whether it works or not…
Any feedback or experiences? Please chip in!

9th Sept. 2018:-

This pic shows my poor Lupin before I sprayed it with a very weak solution of HP (5ml of 9% in 500ml tapwater).

I’m starting with a very low dilution because hydrogen peroxide at about 10% dilution becomes something you can use as a weedkiller.
I’ll watch the plant to see what happens…

Only hours later the bugs are coming back! Solution was way too weak to hurt them but it’d be too expensive to use the 9% HP that I bought from the local pharmacy in strong concentrations. I could add soap or other stuff but that would spoil the purity of the experiment?

I think I need to go online & buy the strongest concentration I can in larger amounts!

10th Sept. 2018

Looked into that… In the UK it appears you can’t buy HP over 12% without a Government licence. 10% would make the dilution maths easier for me but I need to buy cheaply in larger amounts to make using it a viable alternative to less Green alternatives. More research needed…

11th Sept. 2018:-

I’m still thinking that if I can burn aphids off without killing my plants & leaving no chemical residue apart from water & oxygen is a viable option, it’s worth chasing even though it may not be cheaper than conventional insecticides?
I’m not good at chemistry or the calculations involved, so I mithered all my local pharmacists for insight into how to get sensible measures of strength.
They were very helpful but not entirely useful until I thought about what they all said.
As a gardener I want to err on the side of caution the same as chefs say that underseasoning can be fixed, too much can’t.
To get to the ’I’ve learnt stuff’ bit… I’m treating the pharmacy available 9% as 10% for easier maths but then thinking of it as 1% & just moving the decimal point. So 10% becomes pure in dilution calculations if I also move the decimal point in the solution (tap water) .
So 20ml of shop bought 10% HP topped up to 200ml with tap water becomes a 1% dilution.
Move the decimal point to the left!

I bought a 10ml syringe for 20p for more accurate measuring & then used stuff I already had around the house for the rest. 20ml of 10% H202 topped up to make 200ml with tap water for a 1% spray. My poor lupins that had been repopulated by aphids being the test subjects…
I don’t really expect it to be fully effective, I think more like 5% will be getting closer to damaging pests. but I’m aware that there are other factors I can’t control like dropping temperatures.

12th Sept. 2018

Having said dropping temperatures might contribute to aphid absence, only half a dozen of the little buggers have made it back to the juicy tips of my sacrificial lupin after spraying with the 1% H202 solution. That’s a huge improvement!
I’ll have to give it a few days to see if they gather again &, of course, it’ll take a fair bit of observation & experiment but I think it’s worthwhile?

More blog posts by darren8

Next post: Hothouse Shelves for my Chilli Collection



My first experiment will be on my aphid ravaged lupins in pots. The infestation was so bad that despite regular spraying with lightly soaped water from a high pressure pump spray they'd be massed again the next day on the tender parts. As a result my lupins barely produced seed.
Will I get better insect knockdown by using a 2% HP spray with tap water & no soap? Will HP damage the plant?
Guess I'll find out by doing it...

8 Sep, 2018


This seems like a sensible, though more enthusiastic, site that gives good info:

8 Sep, 2018


My aunt used peroxide in her hairdressing salon. I can smell it now.
I've never heard of it being used on plants. I hope it works.

9 Sep, 2018


I've been using it to water my daylily seeds. The 3% type from the chemist. It's supposed to keep away any bacteria. Quite a few people recommend it with regard to germination of seeds.
We'll see if it works.

9 Sep, 2018


I read about it some months ago and was so impressed I bought four bottles! However they are still in their original wrapping because Life intervened. I must read up about its usage now.

9 Sep, 2018


Thanks for this - I have looked it up and it seems it might help powdery mildew
I have a real problem with this on my Penstemons so I think I will give it a try as below.

How to Use Hydrogen Peroxide to Kill Powdery Mildew
By Joshua Duvauchelle

Powdery mildew doesn't just give your plant's foliage a dusty white look; it can stress and kill your plants if it's not controlled. Caused by fungal spores, the mildew can quickly spread from infected plants to the plants beside it. Although powdery mildew can be controlled quickly and effectively with commercial garden mildewcides, those interested in natural home remedies can mix their own mildewcide from over-the-counter hydrogen peroxide.

Step 1
Remove any heavily infested plant foliage and stems that have wilted because of the powdery mildew. Cut off the foliage with a sharp pair of scissors or garden shears and discard them in a sealed plastic bag. Do not shake the foliage, in order to avoid spreading the mildew's spores.

Step 2
Pour a quart of standard 3 percent-strength hydrogen peroxide--available from most drugstores--into a gallon-sized spray bottle. Add three quarts of water and shake the spray bottle to mix its contents thoroughly. If you're using a bigger or smaller bottle, adjust the measurements so you're mixing one part hydrogen peroxide and three parts water.

Step 3
Mist the hydrogen peroxide onto your plants, focusing on areas that have powdery mildew growth. Coat the foliage until there's so much moisture that it beads and drips off of the leaves.

Step 4
Repeat the hydrogen peroxide application once daily until the powdery mildew problem subsides. Then, apply it as needed to control any new powdery mildew growth.

9 Sep, 2018


I use it as a mouth rinse, after I brush. It gives you a bright white smile...also for my plants.

9 Sep, 2018


This sounds great. I will take note, Darren.

9 Sep, 2018


Glad people are finding it interesting! & thanks for all the comments, I could almost stop writing it...
If anyone knows of any useful ways to work out dilutions reasonably accurately it'd be a relief for my addled grey matter

9 Sep, 2018


as a biologist I see it as a harmful by-product of cellular activity. cells have an enzyme to specifically break it down in to harmless water and oxygen. it does decompose into water and oxygen quickly but cells have to do it even faster.
we used it in the labs and it was bought as per volume [20vol being the most concentrated we could buy] and not as a %.
Splashes on the skin resulted in white blemishes that were itchy. so if you do intend to use it please be careful and wash off any splashes especially take care with your eyes.
I have memories of my mum using a dilute solution from the chemists to clear ear wax from my brother's ears!

9 Sep, 2018


That's good advice Seaburn. I've experienced those spillages! It looks like water then you get a sort of frosting on your skin which itches & then gets increasingly sore. Anybody experimenting with it should know that at high concentrations it's highly corrosive, if you splash yourself rinse under running cold water IMMEDIATELY!
As a biologist can you point me to anything useful for calculating dilutions? E.g. as my first experiment on aphids I used 5ml of a 9% solution added to 500ml of tap water. Is there an online calculator, chart or equation I could use so that I know the strength as a final percentage? Most H2O2 dilution calculators online assume that you're starting with 35%. Not sure my local pharmacy sells that...
Always appreciate your feedback, especially on this subject!

9 Sep, 2018


3% does the job for me

9 Sep, 2018


as I said we bought it in at 20 vol strength then we worked from that but we didn't use it on living tissue. so my honest answer is I don't know.
perhaps a pharmacist can help. how % relates to strength in vol I don't know. never needed to. just knew how to use it in experiments and how to keep the students and myself safe from harm.

if you can get the anhydrous powder then 3% can be made by dissolving 3g made up to 100ml.
if you buy it as say a 30% solution then you would dilute it
10ml of the solution made up to 100ml to make a 3%. to keep it 'pure' use distilled water.

10 Sep, 2018


I have been given some special eardrops to use one on Friday and one on Saturday night to go to bed only, its marked on the bottle Bicarbonate of Soda. So I said to the pharmacist 'Why cant I mix up some myself if thats all it is ?' he nearly exploded and said 'No.'
It works well for keeping my ear passages clear of wax and my hearing is much better for it.
Still dont understand.

10 Sep, 2018


because you may get the concentrations wrong and that would inflame the delicate ear canal and ear drum Diane.

10 Sep, 2018


Seaburn would be right Diane, prolonged skin contact at too high a solution would burn & leave you open to infection. Pure HP is actually odourless Hywel, I know the smell you mean (I used to be a punk in the Seventies 😅) but it must be something else that makes the whiff

10 Sep, 2018


I'm obviously trying to read as much as I can on HP so I see some random stuff occasionaly...
Haven't got the link but I read an absolute horror story about a guy that used H2O2 as an anal douche. Never, ever put it inside yourself!!!!! Even in tiny dilutions it's still corrosive over time!!!!
Poor man needed weeks of hospital care, antibiotics to stop him getting blood poisoning through his scorched bowel & stands a chance, in the long term, of having increased his risk of bowel cancer a lot!
As Seaburngirl has pointed out, it's not about the chemical make up, It's about the chemical reaction

12 Sep, 2018


can I just remind you that if you take 20ml of peroxide you need to add 180ml of water to make 200ml of 1%. if you add 200ml then you have a less than 1%. its down to proportions.

if it is a starting strength of 12% then to make a 3% solution then 25ml added to 75ml of water will give you 100ml of 3% solution.

14 Sep, 2018


This has addled my brain. So much easier to just buy 3% from the chemist shop.

14 Sep, 2018


Sorry Seaburn, I'll change that. I meant that I topped it up to 200ml total. Too many late nights...
Not saying you shouldn't do it your way Thorney. Just that I wanted to experiment with HP & record my progress. If I can find effective lowest dilutions then I can do it for less money.

14 Sep, 2018


My sister used HP to bleach her hair. She thought she was Marilyn Monroe incarnate. lol! Wow, imagine the damage it can do internally.

14 Sep, 2018


That's ok Darren. it is a concept that many students fail to grasp and every year they get a question on it!
even those who you see doing it correctly often write it down incorrectly. it used to drive me mad. mind you not as much as powers of ten to the minus....... they would insist on measuring in cm and then forget they were a decimal place out grrr. I banned them using cm it had to be always measured in microns/mm/m. :o)

14 Sep, 2018


I was truly terrible at chemistry in school Seaburn!

14 Sep, 2018


Just found your page Darren, and I gave up growing lupins because of aphids. I may try again this year and use your method.

16 Jan, 2019

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