Ficus and Elm are, as you say, sort of bullet proof. A serious problem I see here with your experience kind of show cases what some seem to think is the proper way to water Conifers. It is aledged that conifers do not like a lot of water. In most cases I would agree to that. However; there are other conifers that do like a constant source of water, while not being tolerant of "having their feet wet".
For years I was informed by the generally accepted cannon on conifer care, that Pines don't like a lot of water. This same thought process lumped Mugo Pines into this while, as a side bar, claimied that Mugos are difficult to care for. The truth is that you cannot treat Mugo Pines as a Ponderosa Pine, or a JWP, or a Japanese Black Pine. I found early on, when I decided to take the tree seriously, a whole list of standard practices accepted as gospel were in fact false and destructive.
Avoiding a long discussion on Mugo care and for the sake of this string we will look at water. I found that Mugos like a lot of water but they do indeed do not like having their feet wet. This creates a dance around soil components where it is necessary to have a well draining soil followed by an exposure to a larger watering schedule. Trying to make up for this trait by turing your soil mix into mud is self dereating. The Mugo needs two traits a fast draining soil provides. Drainage and resperation. Every time you water the water drives the air out of the soil, it's draining from the soil sucks fresh air into the soil and prevents the growth of the fungus that causes root rot. If your soil stays wet the fungus can form, and the tree might get root rot and die. If you hold off on watering, waiting for the mud mix to dry or have a fast draining soil and think to keep the tree dry, some of these trees may die from thirst. For the sake of this post are four trees that need a lot of water, or better put a more frequent watering schedule and shorter dry time. These would be Mugo, and Scots Pines, and some of the Juniper species--- and let is not leave out Hinoki Cypress.
