I have seen a rather wide range of soil suggestions for the Wax Jambu.
Therefore, I did what has worked for me in the past for my other fruit trees; I aggressively augmented my soil with grow mulch/compost, and inoculated the roots with Micorriza.
I water most of my plants 3x week in the summer.
For established trees, I back way off in the wet winters.
Covering the ground around the base of the tree with a good layer of wood mulch will help to retain moisture in the summer.
I also suspect that this plant needs well draining soil.
I have all of my Wax Jambu trees on some sort of slope. This allows excellent drainage and also avoids the collection of cold air in the winter.
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I have not found what I consider to be reliable information about fertilization for the Wax Jambu tree.
I currently feed it with about half the dose of fertilizer that I would give my citrus trees.
However, based on how fast these trees are now growing, I think I might have to cut back on the fertilization.
The soil I use at planting is pretty rich, so I am sure that is a contributing factor.
The Wax Jambu is considered a tropical/Subtropical tree.
Therefore, you should plant this tree in one of the warmest parts of your yard.
Specifically, avoid planting in low lying depressions or heavy shaded areas of your yard that will collect cold air in the winter.
I have noticed that this tree does loose about a third of its leaves in the winter, but quickly grows them back in the summer.