Fruit Walls: Urban Farming in the 1600s

For centuries before modern greenhouse glass, urban farmers harvested solar energy using walls with thermal mass.


| Summer 2017



Espalier

These pear trees benefit from the warm microclimate created by the brick fruit wall.

Photo by Flickr/isamiga76

From the 16th to the 20th century, urban farmers in Europe grew Mediterranean fruits and vegetables as far north as England and the Netherlands. They grew these crops by planting them next to massive “fruit walls,” which stored the heat from the sun and released it at night, creating a microclimate that could increase the temperature near the walls by up to 22 degrees Fahrenheit as compared to the surrounding area. Later, greenhouses built against the fruit walls further improved yields by capturing and storing energy from the sun even more effectively.

It was only at the very end of the 19th century that the greenhouse turned into a fully glazed and artificially heated building. Modern glass greenhouses require massive inputs of energy for heating, especially because they’re often located in temperate climates with cold winters, plus many require artificial lighting and humidity control. Heating a building that’s entirely made of glass is very energy-intensive because glass has a limited insulation value. Even if it’s triple-glazed, glass loses much more heat than an insulated wall.

Fruit Wall Technology

The design of the modern greenhouse is strikingly different than the technology it evolved from. Initially, the quest to produce warm-weather crops in temperate regions  (and to extend the growing season of local crops) didn’t involve any glass at all. In 1561 (during the apex of the so-called Little Ice Age, a period of exceptional cold in Europe that lasted from about 1300 to 1850), Swiss botanist Conrad Gesner described the effect of sun-heated walls on the ripening of figs and currants, which matured faster than when they were planted farther from the wall.

Gesner’s observation led to the emergence of fruit walls in Northwestern Europe. By planting fruit trees close to these specially built walls with high thermal mass and southern exposure, a microclimate was created that allowed the cultivation of Mediterranean fruits in temperate climates. The French quickly started to refine the technology by pruning the branches of fruit trees so they could be attached to a wooden frame on the wall. This practice, known as “espalier,” allowed them to optimize the use of available space and to further improve upon the growing conditions.

These fruit walls reflected sunlight during the day. They also absorbed solar energy, which was then slowly released as heat during the night, preventing frost damage. Consequently, a warmer microclimate was created on the southern side of the wall. Fruit walls also protected crops from cold northern winds, and protruding roof tiles or wooden canopies were sometimes used to shield the fruit trees from heavy rain, hail, and bird droppings.

Peach Walls in Paris

Initially, fruit walls appeared in the gardens of the wealthy, such as at the Palace of Versailles in France. However, some French regions later developed an urban farming industry based on fruit walls. The most spectacular example was Montreuil, a suburb of Paris, where peaches were grown on a massive scale. Montreuil had more than 370 miles of fruit walls by the 1870s when the industry reached its peak. The 740-acre maze of jumbled-up walls was so confusing for outsiders that the Prussian army went around Montreuil during the Siege of Paris in 1870.





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