Answer: Mandarin trees are usually grafted onto sour orange tree root stock so your tree is still technically a citrus tree and as such has the potential to produce flowers and fruit. It probably won't flower until it's about 3 years old. Continue giving it good care and you may end up with a few sour oranges. Even if you don't like the fruit, the fragrant flowers will reward you 2-3 times a year.
Now that you know that over-fertilization is easy to do with containerized plants, how about using a water-soluable fertilizer (such as Miracle-Gro or Peter's), diluting it to half-strength, and applying every 3-4 weeks all year around? This will eliminate the chance of over-feeding and the resulting salt burn.
Best wishes with your citrus!
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