Question
I have had a flowering plum for 12 years.  Two years ago, I had it pruned, sense that time it blooms very little and does not leaf-out in the spring. It is on the north side of the house and in an area that may get too much water as water drains there from the neightbors yard (the soil is bog-like).  Should I have it cut down or can it be saved?

Answer
By "does not leaf out in the Spring' you mean that it has no leaves then it is dead. If you mean that it does not flower in the Spring then that is another story. They do not like soggy soil. If it has no leaves remove it --if it is not flowering I would fertilize the plant.   Most plants need a regular "diet" of all-purpose plant food, either specialty (labeled for your specific plant type) or a generic N-P-K (nitrogen - phosphorus - potassium)

For flowering or fruiting plants, use a fertilizer higher in phosphorous content (middle number) Check with your local nursery for one of these fertilizers.

Without seeing the site I really can not advise you on how to deal with the wet area.