How Do You Treat a Pencil Cactus Turning Yellow?

Pencil Cactus, also known by its Latin name Euphorbia tirucalli, is a bush-like plant native to India and Africa. Pencil Cactus is a popular beginner houseplant as it prefers arid conditions and low humidity.

One of the biggest mistakes Pencil Cactus owners make is overwatering their plant. The soil should be completely dry before you give your Pencil Cactus a drink, as its roots are very susceptible to root rot. Root rot prevents the Pencil Cactus from taking in nutrients, killing the plant.

A Pencil Cactus turning yellow can be caused by root rot from overwatering or old leaves dying to make way for new growth; you’ll first need to assess which of these conditions is affecting your plant. To treat a Pencil Cactus turning yellow, you must remove it from its pot, trim away any rotted roots and yellow leaves, and allow it to dry out before repotting in a new pot with fresh soil.

We’ll look at these causes in greater detail so you can properly diagnose your Pencil Cactus. 

Does a Pencil Cactus Change Color?

Pencil Cactus is also commonly referred to as “Sticks on Fire.” This plant naturally changes color with the seasons and as temperatures cool. In the summer, its branches turn yellow, then orange and pink in the fall (hence its nickname). So if you notice your Pencil Cactus changing color in the fall, it’s perfectly normal!

But a color change is not always good. A yellowing Pencil Cactus may also indicate that your plant has been overwatered. Like other cacti, Pencil Cactus is designed to withstand periods of drought. It’s very difficult to underwater this plant, but eager gardeners can easily overwater it.

Signs of an Overwatered Pencil Cactus

There are a couple of ways that a Pencil Cactus may become overwatered. If your Pencil Cactus is in a pot without drainage holes, the soil will have no way to aerate. This causes the soil to become waterlogged, so the roots begin to rot. 

You may have also planted your Pencil Cactus in the wrong soil type. Regular potting soils retain too much moisture for this plant’s delicate roots. Sandy, well-draining soil is best for cacti since it filters water quickly and stays nice and dry. 

Root rot is not immediately noticeable since roots are below the soil’s surface. But once the roots have rotted enough that the plant cannot take in water or nutrients, the plant will start to turn yellow. This is the first sign that your plant is dying. 

Signs of Yellow Leaves Due to Old Age 

Pencil cactus plant
If you’ve been careful about keeping your Pencil Cactus soil dry, the issue may not be overwatering. Your plant may be simply dropping its old leaves to grow new, healthy ones.

Typically, older Pencil Cactus leaves will turn yellow and brown before they drop off the plant. You can speed up the process by pruning any yellow leaves yourself. If you notice new growth appearing at the same time as leaves are turning yellow, this indicates that old age is the cause. 

Don’t worry too much about your Pencil Cactus aging since this plant can live for decades.

Can a Yellowing Cactus Be Saved?

If you get ahead of root rot before fungus takes over, you can still save your Pencil Cactus. You’ll need gloves, a pair of kitchen tongs, shears, and fresh soil. 

First, remove the cactus from its pot with tongs. The soil will be dense and moist if your plant has been overwatered. Use a brush to remove as much moist soil away from the plant’s roots as possible. The roots will likely have a foul smell. 

Trim away any brown mushy roots you can see. Leave the cactus in the open on a piece of newspaper so the roots can dry out. Once the roots are dry to the touch, fill your pot with fresh cactus soil and repot your Pencil Cactus. Wait two weeks before you water your plant again to give the roots a chance to recover. 

Can You Cut Back a Pencil Cactus?

If the rot has extended from the roots up to the actual stem, you’ll need to remove the rot to prevent it from spreading. Cacti are unique in that they recover from cuts by forming a callous over any open wounds.

Make sure you use a sterilized knife before cutting away any rotten leaves on your Pencil Cactus. You can sprinkle powdered sulfur on the open wound to help it heal as well. Be aware that sometimes the rot goes deeper inside the plant than you realize. Make sure you remove all the rot, or it will eventually travel to the rest of your cactus.

Should I Spray My Cactus With Water?

If you have an abundance of tropical plants, it might be part of your regular watering routine to give them all a misting. Cacti require little to no humidity, unlike tropical plants, which like humidity. Any excess moisture on or around your plant can lead to serious issues like rot or disease

If you’re unsure if your Pencil Cactus is getting enough moisture, consider buying a moisture gauge. This inexpensive tool will let you know how moist or dry your soil is so you don’t risk overwatering.  

Do Pencil Cactus Like to Be Root Bound?

Root bound (sometimes called pot bound) is when a plant has grown so much that its roots have no more space to extend. Some plants cannot tolerate being root bound, while others don’t mind. Plants like Spider Plants thrive and flower better when they’re root bound. 

Like many cacti and succulents, Pencil Cactus doesn’t mind being slightly root bound. Since cacti grow slowly, it often takes years to outgrow their pot. They tend to like small spaces, so you only need to size up pots once you see roots grow out from the drainage holes. When you re-pot your Pencil Cactus, only go up one pot size (1-2 in or 3-5 cm).

Can You Grow Pencil Cactus Indoors?

Euphorbia tirucalli plant
Although Pencil Cactus can grow up to 30 ft (9 m) in the wild, they tend to stay around 2-6 ft (0.5-2 m) tall indoors. Due to its minimal watering needs, Pencil Cactus is an excellent houseplant for first-time gardeners. Pencil Cactus only needs to be watered once every two weeks and even less in the winter. It only needs to be fertilized once a year!

One of the main concerns with growing Pencil Cactus indoors is temperature. This plant is native to arid environments, so a bright, warm home is necessary. Avoid placing this plant in a room with an air conditioner, as the cool air may stress it out. Pencil Cactus also don’t like humidity, so don’t keep your plant near a humidifier or a bathroom. 

How Much Sun Does a Pencil Cactus Need?

If you plan to grow a Pencil Cactus, you must ensure your home has a bright enough space to keep it happy. A Pencil Cactus needs 6-8 hours of direct light daily and is not tolerant of shade. For best results, place your cactus in a south or west-facing window. Make sure you rotate your plant every few weeks, so each side receives an equal amount of light. 

If you’re lucky enough to have a greenhouse in your backyard, this is a great way to ensure your Pencil Cactus receives enough light. Gardeners who live in a climate with long dark winters may want to consider a grow light for their Pencil Cactus. LED grow lights are the best options as they emit light but not heat so they won’t burn your plant. 


Pencil Cactus is one of those easy houseplants that demands very little but provides so much beauty! Cacti and succulents are some of the few plants that can suffer if you give them too much attention.

Overwatering is the number one killer of Pencil Cactus plants. When the plant cannot intake nutrients due to damaged roots, it will begin to yellow and die. But yellow leaves are not always a bad sign. Pencil Cactus will periodically shed its old leaves to make way for new growth.

To treat your yellow Pencil Cactus, carefully remove it from its pot and trim away any rotted roots. Allow the Cactus to dry out before repotting in a new pot with fresh Cactus soil and drainage holes. You can also prune any yellow leaves and your Pencil Cactus will thrive for years to come!