Bacterial infection seen on leaf of Monstera ThaI Constellation

Root Rot Causes & Symptoms in Plants you Wish you Knew

What are the symptoms of root rot? How do you know if your plant’s roots are rotting? These are questions plant parents are asking themselves. As roots are in most cases covered by soil it is not always easy to detect if roots are rotting.

Luckily plants show rotting roots not only on the roots itself but you can also read it from their leaves. Leaves are a telltale for over- and underwatering, infections and other diseases as well as nutrient deficiencies.

There are two main sources of root rot. The first one is overwatering. If the soil is too wet the roots do not have enough oxygen and start to rot. Some plants can be more forgiving than others when it comes to overwatering, but overwatering itself is the biggest cause of death for houseplants.

The second source of root rot is caused by a fungus that lives in the soil and is activated by overwatering multiple times.

The main issue with root rot is that it is spreading to other healthy roots and infects them as well. Once the roots of a plant are rotting, even correct watering and optimal soil humidity might not be enough to keep your houseplant alive as the downward spiral leading to death might have already started.
 

WHAT IS ROOT ROT?

Root rot can be described as a disease that attacks the roots of a plant and is caused by either overwatering or fungus bacteria in the soil. It is seen in both indoor as well as outdoor plants.

However, it is more common in indoor houseplants and symptoms are often shown when it is already too late and roots started to rot. Roots then are often very firm and change colour to black or white and become soft.

The roots decompose and often fall off when touched. A plant that has root rot will stop growing. Many sources describe root rot as lethal which is true but only if you are not taking action.

A plant with root rot can be brought back to life in most cases, but the most important step is to identify root rot as quickly as possible and then take adequate measures to save the plant.

 

HOW DO I KNOW MY PLANT HAS ROOT ROT?

This is the interesting part. You can often tell by the leaves of your plant if a plant has root rot. Wilting, discolored leaves that become small can be a signal of root rot.

Yellowing leaves can also be a good indicator of overwatering whilst black spots with a yellow hue are a good indicator of a bacterial infection.

This is an example of a Monstera Thai Constellation leaf that has a bacterial infection caused by overwatering and rotting roots. You can see the big black spot surrounded by a yellow hue:

Bacterial infection seen on leaf of Monstera ThaI Constellation
Bacterial infection on a leaf of a Monstera Thai Constellation
Rotting roots on plants are mushy and often black
Root Rot Symptoms: Rotting roots on plants are mushy and often black and easily fall off. This is a rooted/rotted Philodendron Glorious cutting.

 

CAUSES OF ROOT ROT

One big cause for root rot to occur in indoor houseplants is bad drainage. We often see amateurs and also houseplant enthusiasts that use pots without drainage holes.

This is a big no-no unless you are absolutely certain each and every time you water your plants that you get the amount of water right.

In addition, bad drainage often leads to root rot as soil that is not well-draining will stay humid and has very few air pockets that provide roots with necessary oxygen. To make your soil well draining you simply need bigger grain-sized material.

What we often use and see eg. in aroid and philodendron cultivation is the use of orchid bark or big chunks of bark in general.

In addition pumice and perlite help to break up soil and make it more “airy” and well-draining. A good indicator of well-draining is to count the seconds after watering your plants until you see water coming out of your pot.

Whilst using well-draining material you will see water flowing out of your pot almost immediately. Soil that is very dense on the other hand will keep water and soak like a sponge. The soil will get soaked.

Overwatering itself is a big cause of root rot. Actually it is not always easy to know when your plant had enough. There is a natural tendency to mean it too good and water your plant too much too often.

A good indicator to see if your plant needs water is to stick your finger into the soil and see if the bottom 1/2 inch of your potting medium is wet to the touch. By wet we mean wet and not soggy. If it is slightly wet not watering is needed. If it is dry water your plant. This sounds simple but you may need to develop a feeling for it.

Not enough light can cause root rot as the water provided cannot be used by the plant as the photosynthesis is slowed down or stopped. Your plant will sit in water for too long and it will cause root rot.

We once had a ZZ plant that was moved from a bright location to the bedroom which was rather dark. We kept the watering schedule the same and it led the roots of the ZZ plant to rot as the plant itself just needed much less water in the much darker spot it was moved.

Too big a pot. We cannot stress how important it is too chose an adequate pot size. If the size of your pot is too big it is just extremely difficult to water your plant too much and then have to worry that root rot is developing. As the roots of your plant do not get to most areas in a way too big pot the water will accumulate and stay in these areas.

This can lead to an activation of fungus bacteria or you can suffocate the roots of your plant because of the presence of too much water in the soil. It is, therefore, best to choose and adequate pot size for your plant and graduate 1-2 pot sizes each time your plant is about to outgrow the current pot.
 

TYPES OF ROOT ROT

As already stated there are two main causes of root rot. Firstly overwatering and secondly a fungal infection:
 

Overwatering

Overwatering plants and thus soggy soil leads to a lack of oxygen in the roots. They will rott and die back. Most importantly it often spreads to otherwise healthy roots and rotts them also.

 

Fungal infection

The fungus in the soil can lay dormant for multiple years and is activated by overwatering once or multiple times. The fungus then attacks the roots starting from the tips. The roots decompose and decay and if you touch them with your hands they will often fall off and feel soft to the touch.
 

SYMPTOMS OF ROTTING ROOTS

This is a list of the symptoms of rotting roots in plants:

  • Wilted leaves and dying back plants
  • Stunted growth
  • Yellowing leaves
  • Black spots on leaves with yellow hue
  • Chloriosis of lower leaves
  • Dull leaves
  • Brown and mushy roots

Please bear in mind that some of the symptoms also stand for other diseases or even malnutrition. Eg. yellowing leaves can be a sign of over- or underwatering and do not necessarily mean that your plant is overwatered. Sticking your finger in the dirt will quickly help you to rule out some of the causes.