Pencil Cactus (Euphorbia tirucalli) Turning Yellow – Top 3 Causes & Remedies is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon and the Amazon logo are trademarks of, Inc. or its affiliates.

Pencil Cactus, known also as “Sticks on Fire”, or “Milk Bush” is a unique and interesting succulent that will catch the eye of every visitor of your house. Native to semi-arid tropical climates, it isn’t particularly demanding when it comes to soil quality or some special treatment. Even inexperienced growers can enjoy the captivating beauty of this cactus, that is naturally green indoors, but will turn to beautiful red color in summer season. Turning red is completely normal for this succulent. Turning yellow isn’t though, and in this post we will outline why it happens, and what you can do save your Pencil Cactus.

Before we dive into details, let me briefly summarize the three main reasons why your Pencil Cactus may turn yellow: Over-watering (which causes root-rot) is the no. 1 reason, natural aging no. 2 (these cacti can live decades, but they aren’t immortal), and specific fungal infection no. 3, and the less likely reason. Let’s have a look at all three issues in detail, so you can identify the culprit, and address the yellowing of your favorite cactus.


Over-watering as no. 1 reason of Pencil Cactus (Euphorbia tirucalli) turning yellow

Many people mistakenly think that when a plant turns yellow, it lacks water. This is no doubt true for many plants in the garden, and trees in the forest, but succulents are exception to the rule. Native to semi-arid areas, it is almost impossible under-water this cactus, since it is used to surviving long periods of drought. Plant strength can sometimes become its weakness though. Kept at home, or in a garden, especially outside of its natural habitat, it is very easy to over-water this cactus. The events unfold in the following manner:

  • You give your pencil cactus too much water too often, or even not but have it indoors in a pot without a drainage hole. In both cases the soil remains constantly moist or even wet.
  • In such a wet soil the roots of your plant will start to rot. This process can be slow, and you may not notice anything for quite a while, thinking that you treat your pencil cactus well enough.
  • When the root rot advances, the root system isn’t able anymore to transfer water and nutrients to the body of the plant. It dries from inside, turns yellow, and the cactus will eventually die.
Pencil cactus in its natural environment, turning red during summer season

Addressing over-watering in a pencil cactus

Whether or not you can save your pencil cactus depends on the severity of root rot. If it has advanced to some stage and basically all the roots are rotten, you cannot really do anything except of learning a lesson, and do things better with a new succulent. If you spot the problem relatively early, however, you still have a chance to save the plant. Make sure to do the following steps:

  1. Remove the cactus from the original pot, and clean the roots from all soil.
  2. Cut away all rotten roots, but leave the parts of the root system that are still healthy on the plant. You should never cut away all roots whatsoever, because plant needs roots to gather nutrients from the soil, and water.
  3. Plant the pencil cactus in a new pot, in a dry soil, some good potting mix for succulents. You should also use a pot with a drainage hole.
  4. Water it heavily but just once, and then wait for the soil to completely dry, and just then water again. Don’t forget to always empty the saucer after watering. The key is to make sure that roots take some water, and then they stay in a relatively dry soil, and the rotting won’t continue.


Aging as a no. 2 reason for a pencil cactus turning yellow

Some succulents can definitely outlive us. Growing slowly and enjoying their time on this marvelous planet, succulents can sometimes live up to 200 years. Of course it depends on the specie, and also growing conditions and everything, but it is fair enough saying that a plant can accompany you for your lifetime.

Pencil cactus can live for decades, and when it starts turning yellow simply because it is old already, and readying for a transition to the other world, the heaven of plants :), you cannot do much except of congratulating yourself. It isn’t common for us to outlive our succulents, so you likely did a good job with this cactus. What confuses some people is that they bought the pencil cactus just ten years ago and not it turns yellow.

The thing is that you do not necessarily know the age of the plant you are buying. Maybe it was ten or twenty years old when you bought it, they just pruned and shortened it regularly, hence it appeared small and young. Mark my words: if you rule out over-watering, it is highly probable that your pencil cactus has simply aged, and it is time to say goodbye to it.


Rare fungal infections can also cause the pencil cactus to turn yellow

Fungal infections and root rot often go hand in hand, but in some cases just the upper part of your plant can be affected. Pencil Cactus isn’t prone to pests and infections, but we should realize that we often grow it in environment that’s far away from its native land. Hence it may come in contact with pests and fungi it isn’t used to, and if the contact happens when the cactus is vulnerable–for example after winter, or after some stress caused by mechanical damage or extreme temperature change, the infection can find its way into the plant.

When you rule out over-watering and aging as reasons for the undesired changes in the color of your cactus, you should consider the option that it got infected with some fungus. This isn’t a likely cause, and it will be responsible for one in a hundred cases, but it is a possibility we cannot simply rule out. And I don’t have good news for you:

In a case of infestation of your pencil cactus, the best thing you can do is to throw it away, together with the soil. You should also disinfect the pot afterwards. The thing is that these fungal infections aren’t easy to treat, and they can jump to other plants in your house, which is likely the last thing you want to witness. That’s why I suggest you to simply get rid of an infected plant, unless it is a super rare and expensive succulent (then it makes sense trying to treat it). Pencil cactus does not fit this category though.


Final thoughts

When your Pencil Cactus (Euphorbia tirucalli) starts turning yellow, it is always a reason to pay closer attention to the plant. This particular color change doesn’t signify anything good. In most cases it is a result of a root rot, in less likely cases your cactus simply aged and will die soon, and in even less likely cases it is infected with some fungus. I hope that after reading this article you can easily identify the cause of the yellowing of your cactus, and will take action accordingly. Thank you for reading, and good luck with your plants!


May also interest you: