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Problem Solver: Fruit Coloration

Cooling nighttime temperatures trigger the appearance of orange and yellow hues in the rinds of citrus fruits.  In temperate climates that have gradually cooling nighttime temperatures toward winter, fruit coloration is generally a good indicator of ripeness.

In tropical climates and also in many indoor growing situations, fruit coloration may not be the best indicator of ripeness because the tree is not receiving the necessary climactic cues for fruit coloring.  This is why the Mexican (Key) lime is harvested green in the more tropical areas of Mexico and Florida where it is grown commercially.  These limes are ripe when picked, even though they are still green.   Limes in California and other areas that receive cooler temperatures during the ripening season, will actually turn yellow when ready to pick. 

Like most citrus, lemons are green as they develop, then turn gradually to yellow when ripe. (Extremely ripe Meyer lemons actually take on a lovely orange hue.) Once mature, most lemon varieties will hang on the tree for several months, slowly growing larger and developing thicker skins.

When coloration is not a reliable indicator, ripeness can be determined with other methods.  Look for the development of a dusky appearance on the rind of ripe fruits.  The final determinant of ripeness will be how the fruit tastes.  Sampling is often the most reliable indicator of when to harvest.  Remember that citrus do not ripen further once picked.