Here in the subtropics, citrus go dormant, flower in the spring and produce fruit in the fall. All predictable but what do they do in the tropics where there is no spring fall or winter? I have spent 7 years in the tropics and I can tell you that it is hot and wet or hot and dry, so how do citrus know when to flower and set fruit? If they are growing in a greenhouse, could you change the timing or does it have to do with the length of each day?
Karl

Stress in any form can trigger the blooming and fruiting cycle. In the tropics when it is rainfed, the pattern of wet (monsoonal rains) and dry (markedly less rainfall) seasons are often enough to trigger blooming. If irrigated, one can control the amount of water to cause a little bit of stress. In the subtropics, it is triggered by the cold temperature followed by warming temperature at seasonal scale.

Joe
I didn’t think that it was that simple but what you say does ring true with what I have read about apple trees. I believe it was applenut (Kevin Hauser) that said that you could make a tree produce fruit by making it think that it will die. I believe that he said to cut off the water supply to do this.
Karl

In addition to Joes posting, besides the dry season in the tropics causing the blooming and fruiting cycle, further due to the constant high temperature and humidity, citrus do not turn orange, but remain green (sometimes with a few yellow patches). Therefore it is difficult to determine which fruits are mature and which are still unripe. An orange that was grown in the tropics does not have a very healthy look to it. Most Americans would never buy them because of their rather poor looks.

But the fruits that I tasted are very sweet even though the peels are green in color. And mostly none are seedless. The citrus that I tasted including pomellos have seeds in them. And last they are not entirely green some have the tinge of yellow or dull orange when they geto ripen.