Question
I have a pot with three Barrel Cactus. The tallest, about 3 feet and the next tallest slightly shorter, are both shrivelling and turning black at the top.  Am I watering it too much or not enough?

Answer
Jo,

Damage to the apex of the plant is usually caused by either cold damage or sunburn. Was your plants exposed to any cold temps over the last few months? It can take a while to show damage. Or, did you just put them outside in direct sun? Cacti do not automatically like direct sunlight and have to be acclimated to it.

If it is neither of those, it could be from over watering, but it that is the case, the rot is usually from inside which means that the plant will perish. Generally speaking, cacti should only be watered when the soil is dry. Hope this helps.

Sincerely,

Greg