Q.gardenias not doing well
I have 3 large Gardenias that are 15 plus years old growing in pots. I have already lost one. The stem broke off at ground level and the roots were almost like wood pulp. Can you tell me what this could be?

Your gardenias may be suffering from root rot, possibly caused by over-watering. For more information on root rot, please visit the following link:
https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm
I am going to recommend that you carefully examine the root systems of your other two gardenias as a precaution and treat them for root rot (if you discover it) using the information in the above article.