You haven't specified whether the plant is potted or not, so I'll just assume you're asking about potted cactus. When the body of the cactus starts to soften, shrink, and get wrinkly, it's a sign that there's not enough water in the tissues of the... read more
Cacti with coccid scale infestations often shrivel up somewhat and may even die. The cactus longhorn beetle also feeds on cacti plants, causing damage and shrinkage along the edges of prickly pear pads. They also dig into cactus roots, causing the plant to collapse downward somewhat and shrink in size. read more
Positioning a cactus at the same soil depth it was grown at in the nursery or a previous container is crucial, although it is perhaps tempting, especially with columnar cacti, to bury enough of the stem to hold it securely in place or match the heights of multiple cacti. read more