Root rot is a common issue for all growers and lovers of plants. Comparatively, root rot is more common in potted plants than non potted plants. Since root rot can affect a plant growing in any system including hydroponics it’s important to be aware of it and know how to identify, prevent and treat it. If you don’t know how to recognize root rot or how to treat it, you have come to the right place!
First things first, root rot is preventable if precautions are taken and it’s often treatable. However if left untreated or in extreme cases the plant that is affected may die within 10 days.
What is Root Rot?
Root rot is a plant disease that spreads very quickly and causes the roots of that plant to rot and decay over time. Root rot is essentially caused by a lack of oxygen due to the plant's roots getting saturated. Without oxygen the roots will suffocate just like humans would without oxygen and the plant may die. An environment without oxygen is known as an anaerobic environment and root rot is caused by certain fungi species that thrive in anaerobic conditions. So once root rot starts the less oxygen there will be which sets up a perfect environment for fungi to grow and multiply, taking over and killing the plant.
There are a variety of well known fungi species that cause root rot including Pythium, Phytophthora, Rhizoctonia and Fusarium. Most fungi thrive in moist soil with a warm temperature of 70 degrees Fahrenheit (approximately 21 degrees Celsius) or higher and high humidity so it’s important to try and avoid this. The symptoms of root rot disease can vary depending on the type of root rot but the term root rot covers all the different types.
Unfortunately root rot is contagious, meaning it can be spread from one plant to another. Due to this is it important to be aware and able to identify root rot quickly so your other plants aren't impacted as well. Now you might be asking yourself how is root rot contagious, more specifically how is it transferred from one plant to another? Root rot spreads in two different ways.
One way that root rot is spread is by giving off tiny spores that are airborne and can potentially lead to infecting your entire crop. Additionally, these spores can be transported by insects or dirty gardening tools. This is why it’s important to clean all gardening tools after every use.
The other way that root rot spreads is through water underground or below the surface travelling between root systems. It germinates on the go so once it reaches the next root system it’s ready to grow and multiply. Thus continuously spreading from plant to plant until you identify it, treat it and prevent it for the future, which will all be explained further down.
In general, plants that are in close proximity to each other are at much higher risk of transferring root rot from one plant to another than plants that are further apart.
What are the Signs and Symptoms of Root Rot?
Root rot starts by affecting the plant's root system and over time the signs and symptoms of root rot are able to be seen through the plant's leaves and overall appearance.
This disease is tricky as its first signs occur in the roots that are either covered up or underground making it hard to see and monitor. Due to this, root rot is often identified when symptoms start to appear on the leaves of the plant.
As root rot shows different symptoms on different parts of the plant it’s important to be aware of all signs and symptoms of the plant. Because of this we will discuss the signs and symptoms of the plant's roots, leaves and overall appearance separately.
Signs and Symptoms of Root Rot in the Plants Roots
This will be the first place root rot can be identified. In order to identify roots with root rot it’s first important to know what healthy roots look like.
Healthy roots appear to be a white or tan colour, firm and have no apparent smell to them. The three basic components to healthy roots include oxygen, nutrients and the right temperatures.
However, roots that are suffering from the plant disease known as root rot, appear to be brown and soft (mushy) and may have a distinct rotting or swampy odor to them. Additionally, these roots will also have slowed or stunted growth and if touched, affected roots may fall off.
Signs and Symptoms of Root Rot in the Plants Leaves
After root rot has affected the plants root system it will start to move its way up to the plants leaves. This is commonly when root rot is noticed. Just like before, it’s easier to identify root rot when you know what it looks like but also what it looks like as a healthy plant without root rot.
Healthy plant leaves with the exception of variegated or bi-coloured leaves should display physically firm and green with a bright even colour.
Leaves on a plant that is suffering from root rot are very easily noticeable.
These leaves may include:
- Burnt or dead edges or tips
- Leaves may fall off or be stunted in growth
- Abnormal growth
- Leaves often wilt and curl up or down
- Pale colour or have new leaves developing yellow growth
- Lower older leaves may become yellow
- Brown or dark spotting on the leaves
Root rot can also commonly look like underwatering, as the plant’s leaves will be wilted. The leaves are wilted because they are unable to get water, as the roots are so damaged. If your plant looks wilted in a hydroponic setup, make sure to check the roots. If growing in soil and the leaves are wilted and the soil is wet, make sure to check the roots.
Signs and Symptoms of Root Rot in the Plants Overall Appearance
After root rot has taken over the root system it will also move up to affect the leaves like described above but also the overall plant structure. We will also compare what a healthy plant appearance looks like compared to a plant's appearance that is suffering from root rot disease.
A healthy plant's overall appearance should have a full and bushy growth pattern.
On the other hand, a plant suffering from root rot will display weak stems with the whole plant wilting or drooping as shown above. Plants with root rot will also experience slowed or stunted growth of the overall plant due to the inability to absorb water caused by root rot.
What are the Different Causes of Root Rot?
There are four main causes of root rot that can be easily managed and prevented. These four causes that will be explained further can also have a domino effect on one another. For example, as you will learn overwatering may cause poor drainage which can cause a lack of oxygen for the plants roots and this lack of oxygen can promote growth of bacteria and fungi.
One cause of root rot is overwatering. The exposure to excess water causes water logging interfering with the aeration of the roots and causing low oxygenation and thus decay.
Another cause of root rot is poor drainage. This is very similar to overwatering as the water has no where to exit and therefore keeping the soil moist, and thus this extra water occupies all pore spaces between the growing media and causes water logging which leads to lower aeration and thus decay of the root system.
Additionally, lack of oxygen is another cause of root rot. If you are a grower using a hydroponic set up this will be the main cause of root rot. A lack of oxygen can occur two ways. Most often for plants grown in soil water can fill all of the macro and micro pore spaces in the growing media and it pushes out all of the oxygen. When considering a hydroponic system another way a lack of oxygen can occur is when the air stone or air bubbler that provides oxygen to the water isn’t working or needs to be replaced. Without this oxygen present, processes such as nutrient and water uptake all worsen making it detrimental to the plant. Once the root cells die this opens another door for pathogenic bacteria and fungi to smother the rest of the living roots leading to the last cause of root rot.
The last cause of root rot is proliferation of fungal growth. If plants are grown in a soil, the low oxygen that is needed to cause root rot also triggers the fungi that is naturally in the soil to overgrow and multiply. Some of these fungi include Pythium, Phytophthora, Rhizoctonia, Botrytis, Alternaria or Fusarium which all work to weaken roots and thus infect the plant. After infection the roots are unable to take up water, oxygen or nutrients leading it to be detrimental to the plant.
How to Solve Root Rot in a Hydroponic Set Up
In hydroponic setups root rot occurs when the water isn’t properly aerated. In order to properly aerate your water it’s important to use an air stone or air pump. These air stones create more bubbles in the water which creates surface movement which is useful in increasing oxygen in the water helping the plant grow.
However if root rot does occur these are the steps you will want to take.
- Remove your plant from the hydroponic system and run the roots under water in order to remove dead roots and extra debris. Any roots that are mushy to the touch and easily pull off the plant should be removed.
- Take sterilized scissors and cut back the remaining roots that are infected with root rot that did not easily pull off the plant’s root system (recall these will be brown mushy roots).
- Empty out and clean your water reservoir as well as any tools or other equipment used.
- Spray the roots with hydrogen peroxide as it helps to add oxygen back into the roots helping to kill the root rot. You can also consider adding a small amount of hydrogen peroxide directly to the hydroponic set up or you can dilute it and add it to a soil grow.
- Set your hydroponic system back up.
Tip: if the plant is quite large consider cutting back some leaves so the plant can focus more on rebuilding its root system then supporting so much growth.
Some other tips to prevent root rot in a hydroponic system include changing the water in the reservoir every two weeks or more frequently. Ensuring that the water reservoir is covered from lights and can consider lowering the temperature so it makes it harder for fungi to survive.
Tip: For cannabis growers lowering the temperature at which your plants grow can also give you purple buds.
Check out one of our new products in our store! The air stone. This product can be used in a Grobo or other hydroponic setup.
How to Prevent Root Rot
This is the easiest and best way to deal with root rot, make sure your plant doesn't develop it in the first place by learning how to prevent it!
When keeping roots healthy and preventing root rot there are four components to also keep in mind: oxygen, temperature, water, and nutrients.
As a new grower or new to plants this may catch you by surprise. Plants actually take up oxygen through their roots by the process of respiration but take up carbon dioxide through the process of photosynthesis on their leaves. This being said oxygen is essential for the creation of ATP that helps transport chemical energy throughout the plant. Without this oxygen being uptaken by the plant's roots the plant wouldn't be able to move energy and essentially starve, killing the plant. This anaerobic or oxygenless environment is also when certain fungi start to thrive causing root rot.
Tip: if growing in a hydroponic system, make sure the water is oxygen rich by using an air stone to constantly aerate the water.
Knowing the temperature that your plant thrives in is important for the overall health of the plant as well as developing a healthy root system. When growing cannabis the temperature to aim for is 75°F (24°C).
Lowering the temperatures also allows for more oxygen to be held within the water. If the temperature is kept 72°F (22°C) or lower it will greatly reduce the changes of root rot.
If growing in soil there are a couple things you can do to keep the temperature ideal. First would be to place a fan under your canopy and an exhaust above to promote a healthy air flow around your plant. A lack of circulation can cause hot spots that may drive up the temperature of your plant. Another way is to use a thermometer or if growing outdoors add mulch and hay to cover the topsoil to help insulate the plants roots.
In order to prevent root rot in a hydroponic system the temperature of the water is suggested to be between 66°F and 77°F (19°C and 25°C). These temperatures correspond to better nutrient uptake and faster growth. There are a couple ways to keep your reservoir between these temperatures. You could paint your reservoir white as white reflects heat helping to keep it cool. Adding cool water to the reservoir or investing in a hydroponic water chiller also helps to keep temperatures cooler.
As roots constantly search for water and nutrients to grow, it’s important to monitor how much water you are giving to your plants. Root rot isn't caused by the amount of water you give your plants, it’s about how frequently you water.
For soil growers as the plant grows larger you will need to increase the amount of water you are giving to your plants. We recommend for soil grows to fully saturate the soil, and allow the water to drain from the drainage holes at the bottom of your pot. This ensures all the roots get enough water. Next, make sure to allow the soil to dry out slightly before watering again. This will allow oxygen to enter the macro pores, preventing the creation of an ideal environment for that bad fungi to thrive.
In a hydroponic setup it’s recommended to change the water reservoir every two weeks or even more frequently. Also, as the water needs to be consistently aerated to provide the roots with oxygen. An air stone or air bubbler are often the best bet to ensure the roots are getting enough air to respire and grow healthy.
You may first think of nutrients as helping the plants vegetative growth and bloom but they are just as important in developing a healthy root system. The two key nutrients to root development and helping to strengthen existing roots are phosphorus and potassium. You can add additional nutrients by purchasing a fertilizer. Make sure to follow the instructions on the product as adding too much can burn the plant.
However if you grow using a Grobo this is something you will never have to worry about as the system takes care of this for you.
Overall, root rot can be a scary concern for new growers, but it is easy to prevent and treat. With practise, you will get better at identifying it and treating it. If you don't want the stress of dealing with root rot, consider a Grobo.
Grobo is an automated hydroponic grow box that makes growing easy. Grobo comes fitted with an air pump and an air stone so you don't need to worry about your plant’s roots getting enough oxygen.
If you have ever come across root rot, let us know your experience in the comments, we would love to hear from you!