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The Water Propagation Hack You Need for Algae

If you propagate your plants in water, then you’ve probably come across the common issue of your water going green. Don’t panic, your plant isn’t turning into the Incredible Hulk… it’s algae collecting in the water. This article will talk you through how you can use hydrogen peroxide solution to tackle algae growing in your water propagations. I've linked everything you should need in my Amazon storefront, to make things really easy for you.

What is algae?

The green colour you find in your water at home is actually made up from lots of tiny little single-celled algae organisms. Algae is often present on your plants before propagation and is known to be in the air and water. It replicates by dividing one cell to become two cells and can multiply quickly.

When algae settles in standing water, it absorbs nutrients from the water to survive and multiply. Each algae cell contains chlorophyll that helps it to photosynthesise and grow.

However, algae doesn’t have the key features needed to class it as a plant, including having more than one cell. It doesn’t grow roots and is therefore classified as a ‘protist’.

Why is algae build up harmful?

Large quantities of algae can be harmful because they release toxins into the water. When the excreted toxins build up in the water, they become dangerous to humans, pets, and plants. If you’ve got algae growing in your water propagation jar, then it’s going to be competing with your plant’s roots for nutrients.

How can I use hydrogen peroxide to control the level of algae in water propagations?

The good news is that you can control algae levels in your water propagations with hydrogen peroxide solution. The solution reacts with the algae to denature the proteins in their cell walls, causing them to die off.

If you’re interested in the science behind it, then the chemical composition of hydrogen peroxide is H2O2. Each molecule of hydrogen peroxide has the same constituents as water (H2O) except with one extra oxygen molecule.

When H2O2 is added to water propagations, the molecule breaks down and reacts with the algae, causing it to die off. The remainder of the original H2O2 solution becomes water (H2O).

What kind of hydrogen peroxide should I add to my water propagations?

So now we’re all scienced out, let’s talk about how you can make this work for your water propagations.

I use 12% Hydrogen Peroxide solution in my water propagations. Many websites will recommend a weaker solution, such as 3%, because it’s safer to work with. I find that the problem with working with 3% hydrogen peroxide solution is that you have to use much more of it.

Using 12% hydrogen peroxide solution requires you to take a few more precautions, because at this strength, it can damage your skin. You also have to add a little more water at this strength to water it down a bit and make it safe to use with plants.

What is the hydrogen peroxide: water ratio I should use in water propagations?

I use a ratio of 1 part hydrogen peroxide to 4 parts water in my water propagations. At these levels, the hydrogen peroxide solution is strong enough to kill off the algae in your water propagation jar and shouldn’t hurt your plants. That said, to be safe, I would empty the jar after 24 hours so that any remaining hydrogen peroxide doesn’t start attacking your water propagation.

I would strongly recommend measuring out your hydrogen peroxide solution in a measuring jug, so that you can see how much you need to add of each liquid. If you want to make 500 millimetres of hydrogen peroxide solution, you will need to pour in 100 millimetres of 12% hydrogen peroxide solution and 400 millilitres of water.

WARNING: Hydrogen Peroxide can also be an irritant to your skin, so I’d recommend using gloves, as you don’t want it to find its way onto your skin and start reacting with it. Try to avoid spilling any hydrogen peroxide onto your clothes, as it is also known to bleach things. Wipe away any spillages on your surfaces quickly or put down a cloth you don’t mind damaging.

Once you have finished handling the hydrogen peroxide solution, leave your water propagation to one side and wash your hands, being careful to dispose of gloves. Wash out your measuring jug by diluting any hydrogen peroxide solution left inside with water, to make it safer to handle.

How long should I leave the hydrogen peroxide to work its magic on my water propagation?

Once your hydrogen peroxide solution has been left for 24 hours in your water propagation, I would recommend pouring it out and changing the water in your jar or vase. You should find that your water propagation vessel is much cleaner than before, and that the dead algae is easy to pour away.

Don’t repeat this process too often or it can cause damage to your water propagation. If the hydrogen peroxide solution has no algae to react with, it can start to attack the roots of your water propagation. This reaction can lead to rot in the roots of your plant as its cells start to break down, having been attacked by hydrogen peroxide.

Will you be trying this water propagation hack to get rid of algae?

Now you’re feeling all scienced out, go give it a try and let me know you get on! If you’re on Instagram then tag me @theplantparlourgram in your stories, reels, and posts so I can see the results!

The great thing about using hydrogen peroxide to keep your plants happily rooting is that it’s a completely natural and sustainable way to control algae. If you want to have a go at this then I've linked all the essentials you'll need on Amazon. Did you know that hydrogen peroxide solution can be used for more than just keeping your water propagations healthy? It can also be poured into soil to control pests like fungus gnats and vine weevils.



Hi, thanks for dropping in to read The Plant Papers!

I'm Gemma and I'm the person behind The Plant Parlour. I have a huge collection of rare plants, that I keep in my home in the South of England.

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