Where Does Root Rot Come From?

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Root rot is a bit like pests – it does appear all by itself without any intervention but also…it won’t be able to get a decent foothold without us providing the conditions in which it can thrive.

So whilst it isn’t our fault technically…it also kind of is.

That being said some plants just love to get a bit of root rot. Monstera Thai Constellation bloody love getting a bit of rot – can’t get enough of it. The only thing you can do about that is make a list of which of your plants are predisposed* to root rot and paying closer attention to them.

*Other than Thais, there aren’t many other plants (that I’m aware of) that are more likely to get root rot. However, sometimes factors such as our home environment, our care style etc etc can result in one or two fo our collection being a bit more likely to suffer from rot than others.

What is the main cause of root rot?

I know it’s a cliche, but it’s overwatering. Just this morning I was reading an article on Clever that had this sentence

“People didn’t necessarily realize the care that goes into them apart from just watering them every day”

Dear lord.

I wouldn’t care but the article was about cringy plant trends. Watering every day is a VERY cringy trend, but luckily it’s a trend that takes itself out to the trash when inevitably your plants end up as mush in a month.

Anyway, stop overwatering.

Remember, overwatering can take many forms. It’s not just applying water too often. Other causes of overwatering and therefore root rot are:

  • Too big of a pot
  • Too dense soil
  • Cold environment (especially with high humidity)
  • Low light (again, especially with high humidity)

Is root rot always caused by bacteria?

Yes. Rot doesn’t happen in a vacuum, and it isn’t water itself that causes root rot. Rather, the abundance of moisture and the lack of oxygen that typically follows after extended periods of damp create a great environment for the bacteria to proliferate.

There are over a hundred different types of bacteria that cause root rot, all members of a genus of water moulds called Phytophthora.

As I said earlier, these mould spores don’t spontaneously spring into existence the moment you overwater. They’re airborne, so could fly in through the window, or come in on your pet’s fur, or your clothes and shoes.

They can also live on bugs that are in the soil, but before you go and bleach your soil (jokes, jokes don’t ever do that) remember that soil is an ecosystem that needs bugs. The mold spores aren’t harmful unless they’re in large numbers.

I’m not saying this to scare you, I’m just trying to show that these bacteria are already all around us. it’s up to us to keep their numbers under control.

How easy is it to get root rot?

This is really difficult to answer, especially for newbies, because it depends 100% on the care you’re giving.

If you’re watering your plants everyday, root rot is inevitable, unless you live in a very hot, dry climate. Root rot can turn up in plants that are ‘only’ watered once a week, because that’s often too much.

If you water too much, have your plant in too big of a pot, and keep your plant in low-light conditions, root rot is practically unavoidable.

However, if you make sure to only water your plants when the soil is dry (how dry depends on the plant) you’re unlikely to get root rot. That being said if you’re using super dense soil in a low-light spot, then the plant will take ages to dry and you risk getting root rot.

So many people have asked me in exasperated tones to just tell them how often to water their plants but it’s not that easy.

I have an article here on how often to water house plants, but the tl;dr is…when the soil is dry.

Where is root rot most common?

Root rot is more common in indoor plants than outdoor ones, for fairly obvious reasons:

  • It’s brighter outside, so plants grow faster, and use up the water around their roots
  • The wind dries out soil quickly. Think about how much quicker clothes dry outside compared to inside

Root rot is still an issue to farmers though. One of the species of Phytophora, P. cinnamomi, is extremely aggressive and can cause mass die back in trees.

Does root rot spread through the soil?

Root rot can spread through soil, which is why we usually recommend changing the soil if you have a plant with bad root rot. However, the spores won’t survive in the dried-out soil so I have been known to reuse soil that has been afflicted. Am I recommending you do that? Noooo…but I’ve never had problems doing that.

The key is to properly dry out the soil. There’s no trick to this – I just leave it for a few weeks so it can properly dry out and any old rotting matter has died off.

Be sure to rehydrate the soil before using it (just water it well and then squeeze out excess moisture) because soil can become hydrophobic if it dries out too much.

How long does it take for root rot to start?

Considering the bacteria is likely already in the soil, then practically immediately. However, there are a couple of variables:

How long it takes for the spores to build up to a dangerous population

There are various factors here, but it boils down to how much you’re doing wrong (I’m sorry but I can’t think of a nice way to say that).

Overwatering might itself might not cause root rot for a few months BUT if it’s cold and humid and there’s not much light, then you might see an issue in a week.

The plant itself

Some plants just have weak root systems. It might be a new cutting, or have recently recovered from root rot, or just be…not in great condition. Pests and ill health in general can cause root rot to take hold in a couple of weeks.

When it comes to the actual species of the plant, hardier plants will take longer to succumb to root rot. Snake plants, succulents, ZZ plants will all take a heck of a bashing when it comes to be overwatered.

HOWEVER, with these plants (less so snake plants, but definitely succulents and ZZs) you will have a heck of a journey bringing them back from the brink. ZZ plants have rhizomes that will take a while to start rotting but will disintegrate very quickly.

It’ll be less a case of trying to rehabilitate the plant, and more a case of chopping and propping.

Monstera are pretty resilient to root rot. I’m not sure if they’re popular house plants because they’re resilient or whether years of breeding them has made them stronger. Probably a mix of both.

Final thoughts

Root rot is all around us. It’s in your plant pot right now, possibly even piggybacking on that helpful little springtail.

Quelle horreur.

It’s fine, it’s good, it’s cool.

It’s nature!

Just don’t overwater, and give your plant some sun.

Caroline Cocker

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

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