Home » How to fix Arborvitae root rot – [Thuja occidentalis]

How to fix Arborvitae root rot – [Thuja occidentalis]

Arborvitaer root rot

Arborvitae or by its scientific name Thuja occidentalis, is a perennial plant with very dense foliage, which is why it is widely used to delimit garden areas and create fences. Also known as Thuja, it is characterized by its pyramidal appearance, reddish trunk, flattened branches arranged in a fan shape, and its aromatic needles.


The Thujas actually form a genus of conifers, not only is there Thuja Occidentalis, there are also others such as Thuja Koraiensis, Thuja Plicata, Thuja Standishii and Thuja Sutchuenensis. Although everyone can suffer from root rot, not everyone will be affected to the same extent.

As an example I can mention that Thuja Plicata is the most resistant, while T. Occidentalis ‘Pyramidalis’ can be considered of intermediate resistance and T. Occidentalis ‘Smaragd’ is one of the most susceptible to this problem. But don’t worry, in this post we will see how to solve the problem of root rot in an Arborvitae.

1. Arborvitae root system


If we are going to talk about a problem that attacks the roots of the Arborvitae, I think it is convenient to start this post by learning a little more about the root system of these conifers. Understanding it will help you to act better in the face of the problem.

As a first point I must tell you that the Arborvitae has a fibrous root system. Like most of this type of roots, they are characterized by being very fine.

But that they are fibrous and fine may not be a fact that interests you very much. Specifically, when we talk about roots, what we are interested in knowing is how they extend. That is, how deep they develop and how far they can go horizontally.

In the case of the Arborvitae, they are characterized by having roots that do not extend too deeply, and do not extend very far horizontally either. The degree to which they can be extended depends on the size that the plant can reach, that is, it is closely related to the variety of Arborvitae in question.

For example, in the largest varieties of Arborvitae, roots can develop no more than 24 inches deep. While the horizontal development generally never exceeds the width of the crown, or if it does, it is very little.

2. Causes of root rot


In order to properly treat root rot in an Arborvitae, it is important to recognize the cause of the problem. Let’s see what are the most common causes:

Advice: If you are reading this article on how to control a root rot, it is likely that you will be reading some of the following articles:

2.1 Poorly drained soil


Although these conifers adapt to a fairly wide range of soils, you always prefer them with good drainage. In soils with little drainage capacity, it is very common for the accumulation of water to cause the appearance of rotten roots.

2.2 Excess of water

This cause is similar to the previous one, although here the excess water is not due to poorly drained soils, but because the amounts of water they receive are very large. This can occur in areas with excessive rainfall or when watering in amounts greater than what the Arborvitae need.

Whatever the reason, the result is the same, as the roots will absorb more water than they can process, which can lead to rot.

2.3 Poor drainage of pots

There are varieties of Arborvitae that adapt very well to growing in pots. One key thing to check when growing it this way is that the container has enough holes for drainage.

A pot with few drainage holes will not let water escape and you will end up with a puddle of water inside the pot. Obviously this will end up causing the appearance of root rot.

2.4 Insects and pests

Some insects and pests, such as pine root moth larvae and nematodes, can damage the roots of the Arborvitae and cause root rot. Although it is not one of the most common causes, it can occasionally occur.

2.5 Fungal diseases

There are many fungal diseases that can infect the roots of the Arborvitae and cause their rot, although without a doubt the most common are Phytophthora, Armillaria and Pythium.

Environments with excess water will always favor the appearance of any type of fungal disease. So it will always be key to control the points that we mentioned before.

3. Most common symptoms of Arborvitae root rot


We already know what are the most common causes that can cause root rot in an Arborvitae, but it is useless if we are not able to recognize the problem. In this section I will give you the 5 most common symptoms of root rot.

  1. Wilting: One of the first signs of root rot is the wilting of leaves and branches, which can occur gradually or suddenly.
  2. Yellowing: Arborvitae leaves can turn yellow and drop prematurely, indicating a decline in the overall health of the plant.
  3. Branch dieback: Branches affected by root rot can turn brown and dry, which can eventually lead to branch dieback.
  4. Discoloration of the trunk: The trunk of the Arborvitae can develop dark or discolored spots, indicating that root rot is affecting the plant from the base.
  5. Stunted growth: Root rot can also slow the growth of the plant and make it look weak and malnourished.

If you notice the appearance of any of these symptoms, you should carefully analyze the plant. If you see that any of these symptoms are accompanied by excessively wet soil, it is very likely that there is root rot.

4. How to fix Arborvitae root rot


Once the problem is detected, it is time to act and try to solve it. I am not going to lie to you, depending on the degree of progress of the rot, it is often impossible for you to save the plant, but if you have detected it in time, it is very likely that you will. Let’s see how you should act against the root rot of an Arborvitae.

4.1 Poorly drained soil

If the type of soil is the problem, the best solution will be to transplant it taking it to a place with a better draining soil. You can also add more soil to the base of the tree by creating a slope that allows water to run off and flow away from the tree.

4.2 Excess of water

If the problem lies in excessive watering, it is easy to solve. You should only start to decrease the regularity with which you water your Arborvitae. Make sure that the first few centimeters of soil are completely dry before applying a new irrigation.

In case the problem lies in excessive rain, you can apply the same technique that we mentioned in the previous point. Add soil by creating a slope that does not allow water to accumulate at its base.

4.3 Poor drainage in pot

Poor pot drainage is another easy-to-solve problem. You only have to change the pot or, failing that, add more holes. If you have detected root rot, try to wash and disinfect the pot correctly to eliminate any possibility of diseases or fungi. Take advantage of the transplant to prune all the rotten roots.

4.4 Insects and pests

If the tree is being damaged by insects or pests, the easiest thing to do is to use pesticides or insecticides to kill the pests and protect the tree.

4.5 Fungal diseases

If the tree of life is infected by a fungal disease, it is important to detect what type of disease it is in order to treat it correctly.

  • Phytophthora: causes a weakening of the plant, with its withered and yellowish needles. Under the bark at the base of the plant you can find amber spots, you can also see the root ball turning brown or black. To solve the attacks of this type of fungus, start by watering less frequently, do it when the soil is already dry. You can also apply a special fungicide for this type of fungus (eg fosetyl-al).
  • Armillaria: The general weakening of the plant and the appearance of honey-colored fungus at the base in autumn are the two most common symptoms of this fungus. Unfortunately there is no treatment that can cure a plant attacked by this fungus. It is best to completely remove the plant to prevent possible spread to neighboring plants.
  • Pythium: the most notorious symptom of this fungus is the general wilting of the plant. Although for adult specimens symptoms similar to those of the Phytophthora fungus usually appear. Therefore, to solve it you must act in the same way as for the Phytophthora fungus.
Advice: Before you leave, you may be interested in knowing how to solve any of these problems:

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