We have had two very healthy Portugese Laurel trees growing in our garden, that were here when we moved in 10 years ago (so I don't know how old they were). Last summer, they showed signs of a problem - the leaves started to whither and this spring did not produce any new buds. Before I plant anything else in the bed to replace them, is there some soil testing or something else I should do to determine what killed them? Do such plants have a natural life expectancy and they just died of "old age"? It's odd that they would both die at the same time. Any advice would be helpful.