Is Algae Harmful to Potted Plants?

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Algae is rarely harmful to potted plants.

It just looks a bit gross and messy.

I’m going to tell you something that you don’t want to hear, but it will hugely benefit you if you heed my words:

 Algae will grow in water that's left in the sun.

You know when you have a really dark spot in your house and you want to put a plant in it because it’d look cute as hell but you also KNOW it’ll die?

It’s like that. Algae grows in water. It won’t stop. It’s been doing it for millions of years, and your dreams of a certain aesthetic do NOT factor into its decisions.

Do not spend all your money on beautiful clear pots unless you want to spend your life cleaning them.

I’m gonna assume here that we’re talking about plants that are growing hydroponically (in water rather than soil) but the advice is the same regardless.

Will algae harm my potted plants?

As I mentioned at the beginning, algae itself isn’t harmful to house plants HOWEVER algae needs nutrients to grow. If you have a large build-up of algae you may find that it begins to out-compete your plant, leading to stunted growth.

The solution is simple though: get rid of the algae.

How do I get rid of algae in potted plants?

This is a VERY boring answer, but you need to wash it off. I’m most used to dealing with algae in aquariums (hence why I KNOW that there’s not a lot you can do to prevent it entirely), in which you can use algae scrapers to get rid it.

Algae scrapers aren’t much use on non-square vessels, so you’re better of scrubbing the pot/vase out with a dish sponge. I recommend you have a specific ‘algae sponge’.

I like to use bleach to clean algae, because it, er, kills it.

First off, remove the plant. Bleach in small quantities won’t harm plants (hence why you can use hydrogen peroxide to clean roots off) but let’s not invite accidents in.

Remove as much algae as you can with your sponge, then dip the sponge in some cold water (hot water deactivates bleach) with a drop of bleach and scrub again. You can fill the pot with bleachy water to be extra thorough. Then wash it out and put the plant back.

As I said, the residual bleach shouldn’t harm your plant, but if you’re worried, you can rinse the pot with hot water to get rid of it.

Is there a product I can use to get rid of algae in house plants?

I’ve been asked a LOT if there’s something you can put in the water to stop algae growing aaaand…not really.

The issue here is the same as the one facing aquarists – there’s TONNES of products that’ll kill algae, but not many that JUST kill algae. The aim is to get rid of the algae but to keep your plant/fish healthy.

And since algae is EXTREMELY good at adapting to most conditions, it’ll hang on longer than your plant.

How do I stop algae growing in house plants?

As they say, prevention is better than cure. I’m not sure it’s possible to have 100% algae-free zone, but I rarely need to clean out my hydroponic pots.

By the way, I’m team aquatic plant. I don’t block the light and my plant care regime is…sporadic, so they work super well.

Block the light

This is a trick my boyfriend used to do on the aquarium if the algae got really bad (algae can ‘bloom’ so you can go from having none to a LOT overight).

Basically, you block out the light. In a couple of weeks (or so, depending on the size of the vessel), the algae will die off.

The easy way to do it is to wrap the vessel in black paper. There are other ways, but paper is pretty opaque and doesn’t really insulate the pot and heat up the water too much.

Obvs this will RUIN your aesthetic.

But it does work!

Look after your plant well

Boring but true:

  • The better you take care of your plant the faster it will grow
  • The faster your plant grows the more nutrients it will absorb
  • The more nutrients it absorbs the fewer nutrients are left over to feed the algae

Be sure to use a hydroponic fertiliser for house plants in water. Soil fertilisers can’t always be absorbed by the water roots, but the devious algae will be able to make it work.

Add aquatic plants

This is what I do. I know it’s not *quite* the clear glass vases aesthetic that we aspire to, but if you love keeping plants in water (you don’t need to remember to water them! It’s amazing!) this is the easiest way to stop algae from showing up.

Not only do certain aquatic plants – such as java moss – oxygenate your water, but they also absorb excess nutrients so algae can’t thrive*.

I do have algae in my hydroponic plant pots, so I can’t say that it WON’T grow, but I don’t have a lot and I have, er, never cleaned the glass. If I didn’t have the java moss in there, the pots would no longer be clear, but instead look green.

* You might be worried about getting the fertiliser correct, in terms of having enough leftover fertiliser for the aquatic plants, but not so much that algae doesn’t turn up. In my experience, it’s not an issue.

I did, however, end up with two snails in with my Thai (I assume they hitched a ride on the java moss) and they seem to provide plenty of nutrients so I don’t worry about fertilising. Snails poop a LOT.

My other Monstera gets a bit of nutrient water whenever I remember (every four months? Monstera are fairly apathetic about food) and is growing really well.

Final thoughts

Algae is a pain and looks gross but it’s not an immediate threat. If you hate the way it looks but don’t want to compromise your look, then commit to rinsing your pots out every week or so. You don’t need to add nutrient water back in every time – every four weeks should be fine.

Lazy people, go and grab some java moss.

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