Dreaming of a cactus is usually the indication that you are feeling crowded, or that someone is invading your space, and since the cactus has the prickly spines for defense this represents to the dreamer a wish to establish a boundary and protect your privacy.
A cactus also represents winning out over adversity as it is found in the desert and has adapted itself to hot, dry, growing conditions, thus the dream could be telling the dreamer to adapt to the existing circumstances if he/she cannot change them.
