Arabica coffee is grown in relatively cool climates in the region between the Tropic of Cancer and Capricorn. The optimum temperature is between 15-24 degrees C (59-75 F) year round. Photosynthesis is slowed above these temperatures and frost damage can occur when temperatures hover around 0 degrees C. Ideally, 1500-2500 mm of rain will fall over a nine month period with a three month dry season coinciding with the harvest (Mitchell, 44). Areas with less rainfall can use irrigation to compensate. A period of moisture stress (rain after a dry spell) helps cause homogenous flowering and therefore promotes a clearly defined harvesting season. Countries with more than one wet and dry season will have more than one harvesting season.
There is a direct relationship between extremes of day and nighttime temperatures and coffee quality. Experimental evidence has indicated that a large gap between day and nighttime temperatures is beneficial to the flavor of fruits. Since a coffee cherry is a fruit and the seed is in contact with the fruit, these benefits will be passed onto the seed and therefore into the cup.