First step: computer predictions of microclimates at West Town Farm

Computer model of temperatures on West Town Farm (indicated by black border). Left: Frequency of days where the temperature exceeds 18˚C in West Town Farm area (darker orange indicates higher frequency). Right: Frequency of days where the temperature drops below 0˚C in West Town Farm area (darker blue indicates higher frequency)

When we began our quest to grow edible bananas in Southwest England, we identified temperature as the key obstacle to success. Frost can kill the plants and they also need a period of continuous high temperature to achieve full growth, flowering and fruiting. As a result, we decided to focus our fieldwork on air and soil temperature.

Our priority was to find a site which was unlikely to suffer severe frosts. As a tropical plant, bananas do not have a period during which they are naturally dormant and so their growing parts are not protected from low temperatures. In macroclimate terms, the Southwest is a good choice as it has relatively mild winters, particularly near the coast. However, it does not have the warmest growing season, so maintaining enough heat to produce a crop is a challenge. 

As a starting point, we generated a computer model which predicted the most banana-friendly areas on West Town Farm. The model uses the shape of the landscape to estimate the surface temperature. To do this it predicts how the shape of the land modifies the landscape; it calculates the movement of the sun across the sky, and the heating effect of the sun on different slopes; it estimates the cooling effect of wind in sheltered and exposed parts of the landscape; and it predicts the pooling of cold air at night in depressions and valley bottoms (frost hollows). 

From the maps of microclimate produced by the model we chose the slopes of a sheltered south-facing pasture, known as Easterbrooks, as our pilot site (top centre, just inside the farm boundary). This offered us the highest number of frost-free days and the highest number of days where the temperature exceeded 18˚C.