Thank you for your question. There are many things that can ‘go wrong’ with plum trees, and it would help to know what variety of plum you have (if you know). Plums not flowering is often caused by no pruning. Have you done that? Do you give your tree supplemental watering? Have you checked the leaves and trunk forvinsects? I cannot tell from your photos whether there might be either. UCAL has a great article on the many problems that beset plum trees, that you can read here: http://ipm.ucanr.edu/PMG/selectnewpest.plum.html Since the list is so large, I suggest you contact your county Extension office and decide how to proceed. Here is their webpage: http://cesanbernardino.ucanr.edu Good luck!