It’s actually a euphorbia, and some careful pruning will solve your problem – and result in a more attractive plant
What’s the problem?
I’ve had this cactus for many years, but it keeps getting taller and soon it will hit the ceiling. How can I stop the plant growing without doing it harm?
Diagnosis
The plant in question isn’t a true cactus at all, but a succulent called Euphorbia trigona, also known as the African milk tree. Like many columnar euphorbias, it can shoot up rapidly indoors if it’s happy, often outgrowing its space. Luckily, the plant responds well to pruning if done carefully.