Hi Experts, I wonder if the space is now too little and I have to repot the cactus. What is your suggestion? Thanks for any help. Philip
Difficult to say without seeing the rootball. When the roots grow out of the holes in the bottom of the pot or the pot is so full that it becomes stiff, then you know that it needs to be repotted. My guess is that it a slightly bigger pot would be good for it, and you got it recently it is a good idea to unpot it and look for pests anyway. It looks like something that can grow roots relatively fast, like Notocactus haselbergii or possibly a Rebutia.
