In the tropics I know that coffee requires some elevation, but increasingly coffee is being grown in the subtropics. What are the necessary and sufficient conditions for growing coffee?
I found this website which prescribes the following subtropic and equatorial growing conditions.
The subtropical regions, at high altitudes of 16-24° (Illy, 21). Rainy and dry seasons must be well defined, and altitude must be between 1800-3600 feet. These conditions result in one coffee growing season and one maturation season, usually in the coldest part of autumn. Mexico, Jamaica, the S. Paulo and Minas Gerais regions in Brazil, and Zimbabwe are examples of areas with these climate conditions (Illy, 21).
The equatorial regions at latitudes lower than 10° and altitudes of 3600-6300 feet (Illy, 21). Frequent rainfall causes almost continuous flowering, which results in two coffee harvesting seasons. The period of highest rainfall determines the main harvesting period, while the period of least rainfall determines the second harvest season. Because rainfall is too frequent for patio drying to occur, artificial drying with mechanical dryers is performed in this type of coffee growing environment. Examples of countries that have this climate are Kenya, Colombia, and Ethiopia (Illy, 21).
In addition to the factors mentioned above, it has been shown that the growth and yields of coffee plants depends on shading levels. This is also important regarding the biodiversity and pest rate present in the area. Generally, the more biodiversity and different kinds of shade trees, there will be less harmful pests and better chances of surviving extreme weather conditions (e.g. droughts or landslides). In the Americas, the coffee berry borer is currently the biggest problem, both from a biological and an economic perspective. Hence, it is not just the climate, but also the surrounding conditions that determine whether the coffee plants can grow.