Answer: Citrus trees usually produce more flowers than they can possibly mature into fruit so a majority of the flowers fall without ever forming fruit. Of those that do, nearly one half will fall off before they are one inch in size. Of the remaining, the tree may drop them for no apparent reason, or because of water stress issues. It sounds like your tree is behaving like a normal citrus tree. As it matures it will retain more fruit than it drops so just be patient with your orange tree.
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