There are many factors that go into the flavor of the citrus fruit, including climate, harvesting, fruit variety and pruning.
The fruit need plenty of heat to produce the sugars needed to make the fruit sweet.
Oranges should be sampled before harvesting the entire tree, if they are still sour, allow them longer on the tree to ripen. Tangerines will not ripen further after harvest.
Some varieties of citrus are sour, these crops can be used to make jelly and jams.
Rootstock takeover is possible if the suckers are not trimmed from the tree. Rootstock is generally a more hardy and less tasty variety of citrus.