Question
2 of my 3' potted Mexican fenceposts drooped over and feel spongy. The one
standing is firm. They are in a partly shaded courtyard.

Answer
Michael,

It sounds like they may have rotted, either from too much water or from sunburn. Do you know if the 2 that fell over had any direct sunlight? Did they turn yellow prior to falling over? Is there a foul smell? These are all indications of rot.

It also could be lack of water. In a pot, in summer, most cacti will need water at least once per week (in AZ) and once per 2 weeks in more humid places. Hope this helps.

Sincerely,

Greg