Often cacti are photographed or sketched with their arms pointing upward, but in reality one can find cacti with arms drooping. On a recent hike, there were a few cacti with drooping arms and we got talking and asking the question, what had caused this? 

My research seems to indicate two possible causes: a freeze and/or dehydration of the plant. When our temperature drops into a freeze zone, the point where the arm meets the cacti trunk is vulnerable. As a result it is weakened and the arm will droop as it continues to grow. Another possible cause is lack of water. It is very obvious when a cactus has enough water as it looks a bit plump and when with not enough water, shriveled. So now you know why one cactus will have arms upward and another may not!