Answer: First of all, congratulations on growing the tree! Here are a couple of things you need to know to try to get it to set fruit. Most citrus trees do not begin bearing until between the age of four and six years, so your tree is still young. Some types of citrus will not produce fruit as a small tree, particularly as a small tree in a pot, so part of your success will really depend on the variety of the plant itself. (Luckily many types adapt well to a pot.) Commercial oranges are usually grown as grafted trees to ensure good fruit production, so it's hard to say what potential your particular tree has.
The most limiting factor is often light, so keep providing as much of that as possible all year long. To encourage flowering, if possible keep it where temperatures will be a bit cooler at night, say between 50 and 60 degrees and maintain about 50 percent humidity while it's indoors. Fertilize once a month according to the label instructions alternating between a balanced (eg 20-20-20) and a high-phosphorus fertilizer, taking care not to overfertilize as this can cause lots of foliage rather than blooms. Then, patience. Once the tree blooms, you will have to pollinate by hand (a soft paintbrush works nicely) if it is inside or if outside, allow the bees to pollinate.
Good luck with your tree!
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