This Is Why There’s A Rotten Egg Smell In Your Houseplants

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If its really bad, chances are it’s stem rot.

The description ‘rotten eggs doesn’t do justice to the truly hideous smell stem rot can exude. It smells like rotten eggs/drains from afar, but close up it smells like a thousand creatures washed up on a beach and died.

I noticed a weird smell the other week. It wasn’t constant, I’d just get a waft every now and again. Then it got a bit worse. We assumed there was an issue with our drains, but then it got WAY worse. And was at the wrong end of the house to be the drains.

We were so close to calling a plumber because we were so mystified by the truly hideous smell emanating from the living room. Then my boyfriend stuck his head in my Thai Constellation. I thought he’d collapsed from the smell but no, he’s found the culprit.

My Thai is usually so well-behaved. I put oxygenating aquatic plants in with it so I rarely have to change the water. I talk at length on this blog about how easy it was.

Ironically, I knew the stem shouldn’t be submerged, but it had been for the past 12 months so I assumed it was fine.

I changed the water, but the smell remained. I soaked the whole thing in hydrogen peroxide (killing the moss), which did a great job of loosening all the sheaths of the rotten roots. I thought ah! Root rot! So I trimmed the roots and changed the water. Again. Repeatedly.

Turned out it was stem rot.

Stem rot

I know about stem rot. I’ve written about and experienced stem rot (in a plant I own, not personally).

But there were no overt signs of stem rot. There were signs of root rot, but the stem was still firm, and because the whole root ball smelled like a very ill and violently flatulent seal, I didn’t zero in on the stem.

This seems silly in hindsight, considering a decent amount of stem was submerged, which is not recommended.

I only found out it was stem rot because I scratched the surface of the stem, and the smell that escaped was…a lot. Aaaand then I realised it was stem rot. A stem should be firm, well, like a plant stem. The texture I found on my poor Thai was more akin to a woody mushroom.

Once you have stem rot, you’re pretty much done. The stem ain’t coming back. Luckily I caught it in time, so I cut it as far back as I dared, definitely into non-rotten territory. I then took a couple of maybe cuttings, but a quick sniff a couple of days later confirmed that they were toast. Never mind.

So my Thai is a shadow of her former self (root-wise- her leaves are fine) but the smell has gone!

Luckily I’d been making sure to push all her aerial roots into the water so every node had a root system. I mean, I only have a couple of nodes left, but at least I don’t have to start from scratch.

Root rot

Root rot is the same as stem rot but less advanced. Plants like Thai Constellation are prone to root rot, been if you don’t overwater, but won’t develop stem rot unless you’re really overwatering.

The rotten egg smell is still there, but it’s nowhere near as bad as it is when it’s the stem that’s rotting.

Root rot is caused by too many anaerobic bacteria in the soil. Many people like to completely switch out the soil when they get root rot, but I don’t like to waste it.

Remove the plant, get all the soil off the roots and let it rehab in water. Change it every day to maximise the amount of oxygen the roots can absorb.

Let the soil dry out. Either spread it out evenly, put it in the sun, or just, er, wait longer. Once it’s dry, you can repot the plant. Make sure the plant is in an appropriately sized pot.

This doesn’t 100% get rid of the bacteria. However, their numbers will remain low in soil that doesn’t stay wet for long. Obviously switching out the soil is more likely to guarantee the bacteria are gone BUT if you don’t adjust your care you’ll just have to keep changing the soil.

Stagnant water

Stagnant water can cause that rotten egg smell in houseplants, so don’t let your plants stand in water. Not only can it cause an eggy smell, but you can get creepy crawlies like mosquito larvae* hanging about. If the water is stagnant enough to smell eggy, it’s unlikely to have any oxygen in it, and anaerobic bacteria can proliferate.

*We actually keep a bucket of water outside because fish love ’em

Rotting matter

Using DIY houseplant fertilisers can be a great way of both using up kitchen scraps and saving money BUT it can smell really bad. Rotten banana skins are fine in small doses, but if you overdo it you can end up with a rotting smell that lingers.

Not only will you be treated to the signature rotten egg smell, but you’ll attract fruit flies, the equally annoying cousin of the fungus gnat. Once the banana (or foodstuff of your choice) has rotted, the fruit flies will leave and fungus gnats will move in.

Bananas aren’t even that good of a fertiliser.

I promise DIY fertilisers aren’t worth it, unless you’re actually making a fertiliser, like comfrey tea, as opposed to simply using your potted plants as a compost bin

Final thoughts

It sounds like I’m exaggerating, but the smell of stem rot is…something else. It was a wrench having to chop off so much of the stem – especially since a) it was my fault and b) I should have known better) – but I’m so so glad my living room no longer smells like a thousand whales have farted in it.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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