Why Is My Pencil Cactus Turning Yellow? [What to Do]

Pencil cactuses, also known as Firestick plant or Milk Bush, are eye-catching succulents with branches and stems resembling a pencil. Interestingly, these plants do not belong to the cactus family but to a species called Euphorbia, belonging to the succulent family.

However, their general care is quite similar to that of cactus plants. Although these plants are easy to care for sometimes, they may develop yellow leaves, which may cause plant owners to wonder, ‘Why is my pencil cactus turning yellow.’

So if your pencil cactus is turning yellow, keep reading to learn the possible reasons why.

Why Is My Pencil Cactus Turning Yellow

Knowing why a pencil cactus turns yellow can help plant owners identify and correct the issue before it’s too late. Here are a few potential causes behind why your pencil cactus may be turning yellow:


Overwatering is one of the leading causes behind the yellowing of a pencil cactus. Since pencil cactuses are native to the dry regions of India and Africa, they do not prefer too much water.

The best watering schedule for pencil cactuses is every 10 days in the summer and once monthly during the winter. Since the water may absorb quickly during the summer, a pencil cactus may require more frequent irrigation.

However, the drying process may slow during the winter season, making it critical for plant owners to adjust the watering schedule according to the weather.

The easiest way to avoid overwatering is to create a proper watering schedule and check the top layer of the soil before watering.

If the first two to three inches of the soil are dry, you can water your pencil cactus plant. However, if the top layer of the soil is still wet after 10 days of water, it is best to wait until it completely dries out before watering again.

Brittle branches are another symptom of overwatering. Many people confuse this symptom and think the plant requires more water.

If you continue overwatering your plant for a while, it can develop issues like root rot and mushy branches. If this occurs, you must re-pot your plant immediately and remove the damaged roots and branches to prevent the plant from dying. 

Root Rot

Root rot is another issue that may cause yellowing in pencil cactuses. This condition is closely connected to overwatering — one of the key culprits behind its development.

If you notice your plant’s soil is excessively wet and the branches or roots have begun to turn mushy, that can signal possible root rot. When this occurs, you must immediately remove the plant from the pot and inspect it for damage.

Cut off any mushy, grey, or rotten roots and leave the healthy white roots intact. Use clean shears when removing the rotten roots from the plant. Next, re-pot your pencil cactus in new potting soil for succulents.

If the plant has the appropriate amount of healthy roots, it will eventually return to good health.

Moreover, one of the best ways to avoid root rot is to use a well-draining soil mixture made especially for succulents like pencil cactuses. If you cannot find potting soil made for succulents, you can also make your own by mixing equal parts perlite, potting soil, and sand.

Creating a healthy watering schedule and watering your plant every 10 to 12 days when the upper two to three inches of soil dry can help you avoid issues like overwatering, which eventually lead to root rot.


Injury is a less frequent cause of a pencil cactus turning yellow. However, if your cactus sustains damage due to someone stepping over it, which affects the plant’s ability to distribute water and nutrients; this can cause the injury site to turn yellow.

Moreover, if the injury does not cover a large area, there should be no cause for concern. The plant will ultimately heal naturally, with the damaged site falling off and new growth emerging.


All living organisms age and exhibit various signs of aging. Yellowing leaves indicate aging in pencil cactuses.

Therefore, if you have perfected your pencil cactus watering routine and are avoiding any other factors that may cause yellowing, you probably don’t have anything to worry about as the plant’s leaves are aging.

When the plant’s leaves mature and turn yellow, they fall off, and new foliage sprouts in their place. 

Lack of Sunlight

All plants need sunlight exposure for photosynthesis. A plant transforms oxygen, light, and water into carbohydrates during photosynthesis. Hence, plants cannot create the energy required to survive without sunlight and will die due to inadequate sunlight exposure.

Therefore, a lack of sunlight can cause a pencil cactus to turn yellow. These succulents enjoy bright and direct sunlight exposure and need at least six hours of sunlight to flourish. So inadequate sunlight exposure may be the reason behind your pencil cactus turning yellow.

Moreover, low sunlight can also cause your pencil cactus to develop other issues like root rot. When a pencil cactus does not receive enough sunlight, it tends to stay moist after watering for longer, which can cause the roots to get mushy and rotten.

Root rot can be deadly for your pencil cactus, so providing enough sunlight for the water to dry evenly is critical for the plant’s health. Placing your pencil cactus in front of a south-facing window is a great way to ensure it gets the light it requires to thrive.

Plant owners who live in areas with low sunlight can also utilize plant grow lights to offer their plants enough lighting. However, keep a distance between your pencil cactus and the plant grow lights to avoid scorching the plant.

Moreover, keeping your pencil cactus outdoors during summer can help you ensure it receives adequate sunlight exposure. However, bring the plant indoors when winter approaches and temperatures fall below 18°C.

Pest Infestation

Although pencil cactus plants are not susceptible to pests, they may develop or catch pests like mealy bugs and spider mites from other plants. Pest infestations can negatively impact your pencil cactus’s health and cause them to turn yellow.

Therefore, if you notice yellowing on your pencil cactus, inspecting it for pests can help you determine if pest infestations are the reason behind the yellowing.

Treating a pest-infested pencil cactus with a mild soap-water solution can help eliminate the pests and keep them from returning. You can also use a natural pesticide like neem oil to treat your pest-infested plant.

Important note! It is best to avoid commercially bought pesticides since they may contain harmful chemicals that can harm your pant more than good.

Keep your pest-infested pencil cactus separate from your other plants to avoid your entire plant collection from a pest infestation.


If you haven’t repotted your pencil cactus in a year or two and aren’t providing adequate sunlight or fertilizer, it might become malnourished and turn yellow.

Plant owners who suspect malnutrition are the cause of their pencil cactus becoming yellow can repot their plant in fresh succulent soil to help the plant thrive.

Pencil cactuses prefer soil that is deficient in nitrogen. Therefore, the soil you use for re-potting should be made specifically for succulents like pencil cactuses.

Cold Temperatures

Since a pencil cactus prefers warm temperatures and direct sunlight, it does not react well to cold temperatures.

A pencil cactus thrives between 12°C to 29°C, and exposure to temperatures below 12°C can cause your pencil cactus to turn yellow or shock. The best way to avoid this is to bring your pencil cactus indoors during winter.

You must also keep your pencil cactus plant at a distance from windows that blow in cold gusts of wind. 

Tips for Preventing a Pencil Cactus from Turning Yellow

Here are a few tips on how pencil cactus owners can prevent their plants from yellowing:

  • Create a proper watering schedule for your pencil cactus, and avoid watering before the top two to three inches of the plant are completely dry
  • Inspect the plant during waterings to catch pest infestations early on and treat all pest-infested plants with neem oil
  • Place your pencil cactus in an area with an abundance of bright direct sunlight
  • Use a pant grow light to provide your pencil cactus with adequate light exposure s you live somewhere that lacks sunlight 
  • Re-pot your pencil cactus every one to two years and use well-draining sandy soil made especially for succulents
  • Protect your pencil cactus from drafts and keep it away from windows that blow in cold gusts of winds during winter

Fire Sticks Pencil Cactus 6" Pot Euphorbia - Easy to Grow

Final Verdict

Individuals questioning ‘Why is my pencil cactus turning yellow’ must consider factors like pest infestations, malnutrition, overwatering, under watering, sunlight exposure, age of the plant, and possible injuries to determine the reason behind their pencil cactus turning yellow. Pencil cactus owners can prevent their plants from turning yellow by following the tips discussed above.

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