To dream of a cactus represents situations that you feel are best left alone. Feeling stupid for not leaving something alone or bothering to get involved with something at all. A static area of your life that is dangerous to reopen. Something that is interesting to think about, but dangerous to do. You may be considering doing something that you honestly feel is too scary or embarrassing to be involved with. Insecurity about something that you feel has the potential to be terrible or embarrassing.
Example: A teenager dreamed of having marry a cactus. In waking life they felt forced to study for an exam for a course which they thought failure was an inevitability. They felt that studying or trying the course material made them look stupid for even trying to learn it.