Question
The base of my 10ft tall cactus is cracking upward.  What can i do to stop it and
is it killing it?

Answer
Phil,

Actually what you are seeing is normal. As cacti age, they produce wood, just like a tree at the base of the stem. If the plant continues to grow, the stem must become larger to hold up the weight, so it will crack vertically as it expands. The only other reason for vertical cracks is usually over watering. In either case, it should be just fine. Hope this helps.

Sincerely,

Greg