Pencil Cactus

The pencil cactus (Euphorbia tirucalli) is an interesting shrub with succulent foliage that’s native to semi-arid tropical climates. Indoors, the plant will stay at a more manageable 2-6 feet tall and 1-3 feet wide. Mature plants feature thick brown branches with clusters of smaller green branches at their ends, which are cylindrical in shape and around the thickness of a pencil (hence the plant’s common name).
Care: 
Generally, watering this plant is only necessary a couple of times a month during the warmer parts of the year and even less during the cooler months. The pencil cactus prefers to grow in full sun, meaning at least six hours of sunlight on most days. However, it can tolerate a bit of shade and might even appreciate some protection from the hot afternoon sun. Indoors, grow it by your brightest window. It can also tolerate bright, indirect light.
Watering: 
The watering care for this succulent is very easy. It only needs water every two to three weeks in the spring and summer. Reduce watering to monthly in the fall and winter. It's preferable to let the soil dry out completely in between waterings to avoid overwatering. This plant is highly tolerant to drought, and too much water can rot its roots.