Pencil cactus, also known as the milk bush or Euphorbia tirucalli, is an intriguing and versatile addition to any indoor gardener’s array of plants. Despite its common name, it is not a true cactus but a succulent shrub that’s native to India, known for its distinctive, elongated stems resembling unsharpened pencils.
The pencil cactus is one of the most popular houseplants, distinguished by its long, skinny ‘pencil-like’ stems; hence the name. The plant’s skinny branches are covered with petite leaves that emerge in late spring and early summer, lending it an elegant yet robust appearance.
Although called the pencil cactus, it’s important to note that this plant isn’t a cactus but a succulent. This means it is a drought-tolerant plant, adapting to survive in regions with low humidity. It grows very well in pots, as long as they have drainage holes to prevent excess moisture accumulation and, in turn, root rot.
In late spring and early summer, tiny leaves grow on the pencil cactus’ tips, giving it vibrant appeal. Yet, care is needed when handling this plant, one should always wear gloves, as the plant’s sap, although beneficial to the plant, can cause mild skin irritation. Thus, they are not the best option if you have pets and small children around.
Botanical Name: Euphorbia tirucalli
Common Name: Pencil cactus, Indian tree spurge, pencil tree, milk bush
Plant Type: Shrub
Hardiness Zones: 11 – 12 (USDA)
Sun Exposure: Full sun
Soil Type: Well-draining, sandy soil
Soil pH: Neutral to slightly acidic
Bloom Time: Spring, summer
Flower Color: Yellow
Native Area: Africa, Asia
Pencil Cactus Plant Care
The pencil cactus, or Euphorbia tirucalli, is not a true cactus but a succulent shrub, also known as ‘milk bush’ due to its sap. Indigenous to semi-arid environments in India, it is known for its striking tubular leaves and adaptability to low light conditions.
This succulent prefers sandy soil with good drainage holes to avoid overwatering which can lead to root rot due to excess moisture. Care should be taken to ensure low humidity, protect the plant from cool drafts, and offer full sun to as much direct sun as possible.
Prevent pests such as aphids and spider mites with the frequency of organic houseplant fertilizer, particularly in the late spring until early summer when they are most active.
It’s critical to remember to always wear gloves when handling, since the sap can cause skin irritation.
When it comes to pot size, don’t get too eager to move your pencil cacti to a new pot – they prefer their pots snug and should be repotted using fresh water only when the roots take over the space.
The pencil cactus loves basking in full sun to thrive best, but they’re also tolerant of low light conditions. The direct sun helps to keep the plant’s shrub-like structure and dense foliage in good shape.
If you live in a region that experiences limited sunlight or a lot of cool drafts, it might be best to keep your pencil cacti near a south or east-facing window for maximum sun exposure.
However, in areas with harsh summer rays, partial shade during the peak afternoon hours is advised to prevent leaf scorching. It’s essential to ensure that your plant receives a generous amount of indirect light, especially if you’re growing it indoors.
Pencil cactus thrives best in well-draining sandy soil. As a succulent, it is highly susceptible to root rot, an issue that often plaguing these plants caused by excess moisture.
Adequate drainage holes in the pots are critical to prevent overwatering which can lead to this dreaded disease. The pot size should be in proportion to the plant, not too large as to retain much water.
It might be necessary to transfer the plant to a new pot as it continues to grow. A little organic houseplant fertilizer mixed into the soil in late spring or early summer can also boost the plant’s growth substantially.
Pencil Cactus has a rather particular watering regimen. This striking succulent, popular in India for its low maintenance needs, can tolerate drought conditions, but it doesn’t mean it requires much water.
Under normal circumstances, like in warm temperatures and full sun, watering needs to be done only when the top inch of the sandy soil in the pots has dried out completely.
Overwatering these pencil cacti can lead to root rot, a common issue with succulents kept in conditions of excess moisture, especially when the pots lack proper drainage holes.
Should you upgrade your Pencil Cactus to a new pot, ensure the pot size is proportional to the root mass and it has better drainage to prevent water from stagnating.
Temperature and Humidity
Pencil Cactus is a succulent shrub native to parts of Africa and India. It thrives in warm temperatures and is relatively resistant to drought. What it doesn’t handle well are cool drafts, which can result in dead stems.
Although it can survive low humidity, this plant will definitely appreciate the occasional misting during the heat of summer. Remember to avoid overwatering
Fertilizing a pencil cactus is essential for its growth, especially in the early summer and late spring. However, the frequency of fertilization should be moderate.
An organic houseplant fertilizer rich in nutrients can be used, ensuring that it’s diluted to half its strength. The fertilizer should be added to fresh water before watering the pencil cacti for the best outcome.
Over-fertilizing can lead to problems like root rot and the sap becoming too malleable, which can cause harm to both you and your pets, making it important that you wear gloves when handling this succulent shrub.
Pruning pencil cactus is crucial to maintain its shrub-like appearance while managing its growth.
Always wear gloves when trimming this succulent, as the milky sap can cause irritation. Aim to remove dead stems and prune in late spring or early summer when the plant is in its active growth phase.
The cut end of the stem should be allowed to dry out before placing back into the pot. This prevents the plant from taking in too much water which could lead to overwatering and root rot.
How to Propagate Pencil Cactus
Step 1: Wear Gloves and Cut a Stem
Remember to always wear gloves when handling this plant as it oozes a milky sap when its stems are cut. The sap can be irritating to the skin and eyes, so caution is advised. Cut the stem (or stems) from the parent plant in late spring to early summer.
Step 2: Let the Cut End Dry
After you cut the stem, it’s crucial to let the cut end dry for a few days. This drying period allows the sap to seal over, which will protect the new plant from fungal infections.
By mitigating any possibility of root rot, the new succulent will be better prepared for propagation.
Step 3: Plant the Dried Stem
Once the cut end has dried, the stem is ready to be planted in a new pot. The pot size should be compatible with the size of the stem. Plant the pencil cactus in sandy soil that mimics its natural, drought-tolerant conditions.
Ensure your pot has drainage holes to prevent excess moisture. Overwatering or soil that is too damp can result in root rot.
Step 4: Water and Light Exposure
Once the stem is planted, water it lightly, fresh water free of any contaminants is best. The pencil cactus prefers full sun to low light conditions. However, it is also highly tolerant and can survive in low humidity and tolerate cool drafts.
But remember, just like a true cacti, pencil cacti don’t require much water – overwatering could cause more harm than good.
Step 5: Monitor and Care
After planting, the shrub will require care and attention for successful propagation. The pencil tree is vulnerable to pests like aphids and spider mites, so regular checks are essential.
Increase the frequency of watering during the warmer temperatures of the summer months and consider using an organic houseplant fertilizer for optimal growth.
How to Pot or Repot Pencil Cactus
Step 1: Preparation
Before you start the repotting process, ensure you wear gloves to protect your hands from the irritant sap of the pencil cactus. Choose pots with ample drainage holes to avoid the risk of root rot from overwatering or excess moisture.
Also, the pot size should be proportionate to the size of the plant — a new pot should offer some room for growth but not be so big that the plant’s growth rate drastically slows down.
Step 2: Preparing the Plant
Examine the Euphorbia tirucalli closely for any visible health problems such as aphids or spider mites. Carefully prune away any dead stems at the cut end to encourage fresh, healthy growth.
Remember to do this task in the late spring or early summer when the plant is in its active growing phase.
Step 3: Potting Mix
Prepare a suitable potting mix for the pencil cacti, ideally a well-draining mix like sandy soil. This is because the succulent variety prefers soil conditions similar to its original, drought-ridden environment.
Add a bit of organic houseplant fertilizer to give your plant a nutritious boost.
Step 4: Planting
Place your pencil cactus in the pot and carefully fill around it with the prepared potting mix. Following that, give the plant a gentle watering with fresh water, being careful not to administer too much water.
These succulent species are not true cactuses, but like cacti, they prefer their soil to dry out completely between watering sessions. Adjust your watering frequency according to the plant needs — more in warmer periods, less in cooler ones.
Step 5: Placement
Once potted, place your Milk bush in a location where it will receive direct sun to full sun or low light condition. They are also sensitive to cool drafts, which can lead to leaf drop. Hence, a location away from cool drafts and airflow from air conditioners or open windows is ideal.
Common Pests and Plant Diseases for Pencil Cactus
Despite its drought resistance, like many other succulents, overwatering can harm the pencil cactus, leading to root rot. This occurs when the pot has no drainage holes, or the plant gets much water, causing excess moisture.
This condition results in soft, brown roots and dead stems on the plant. To avoid this, always ensure that your pencil cacti are planted in pots with proper drainage.
Aphids and spider mites are common pests that can distress the pencil cactus. They extract nutrients from the leaves causing slow plant growth or leaf drop. Aphids leave a sticky residue that attracts mold, while spider mites cause yellow, speckled leaves.
Applying fresh water or an organic houseplant fertilizer can control these pests, but ensure to increase the frequency during warm temperatures and lower it on cooler days.
Lastly, if you have pets, remember that the sap of this plant is toxic when ingested.
Common Plant Problems and Solutions for Pencil Cactus
The Euphorbia tirucalli, more commonly known as the pencil cactus or milk bush, may present with brown tips on its succulent leaves under certain conditions. This issue is often caused by low humidity and exposure to cool drafts.
By providing your pencil cactus with a more humid environment and protecting it from sudden temperature drops, you can effectively counteract this problem.
If your pencil cactus is exhibiting yellowing leaves, overwatering could be the culprit. This plant does remarkably well in sandy soil that mimics the drought conditions of its native India.
Ensure your pots have adequate drainage holes to prevent excess moisture and much water leading to root rot. If in doubt, it is better to underwater than overwater these hardy shrubs.
Leaf drop is common in pencil cacti and often due to exposure to drastically low light conditions or direct sun.
These plants prefer full sun to partial shade. If your cactus is losing leaves, consider moving it to a spot where it gets more consistent light, but shield it from exposure to the scorching midday sun.
The sap of the pencil cactus is actually a mildly toxic latex. Always wear gloves when handling this plant and especially when cutting, as fresh water can cause the sap to flow from the cut end.
If sap leakage is frequent, it could mean the plant is experiencing stress, likely due to incorrect light or water levels or an ill-sized pot. Move the plant to a new pot, ideally one appropriate to its size, and adjust lighting and watering accordingly.
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Melissa Pino is a biologist, master gardener, and regular contributor for Planet Natural. Melissa's work focuses on promoting environmentally-friendly practices, helping people create healthy gardens and finding ways to achieve overall health and wellness.