Fruit Walls: Urban Farming in the 1600s | LOW←TECH MAGAZINE
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Picture: fruit walls in Montreuil, a suburb of Paris.
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We are being told to eat local and seasonal food, either because other crops have been tranported over long distances, or because they are grown in energy-intensive greenhouses. But it wasn’t always like that. From the sixteenth to the twentieth century, urban farmers grew Mediterranean fruits and vegetables as far north as England and the Netherlands, using only renewable energy.
These crops were grown surrounded by massive “fruit walls”, which stored the heat from the sun and released it at night, creating a microclimate that could increase the temperature by more than 10°C (18°F). Later, greenhouses built against the fruit walls further improved yields from solar energy alone.
It was only at the very end of the nineteenth century that the greenhouse turned into a fully glazed and artificially heated building where heat is lost almost instantaneously – the complete opposite of the technology it evolved from
The modern glass greenhouse, often located in temperate climates where winters can be cold, requires massive inputs of energy, mainly for heating but also for artificial lighting and humidity control.
According to the FAO, crops grown in heated greenhouses have energy intensity demands around 10 to 20 times those of the same crops grown in open fields. A heated greenhouse requires around 40 megajoule of energy to grow one kilogram of fresh produce, such as tomatoes and peppers Source – page 15. This makes greenhouse-grown crops as energy-intensive as pork meat (40-45 MJ/kg in the USA) Source.
Dutch-style all-glass greenhouses. Picture: Wikipedia Commons.
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In the Netherlands, which is the world’s largest producer of glasshouse grown crops, some 10,500 hectares of greenhouses used 120 petajoules (PJ) of natural gas in 2013 – that’s about half the amount of fossil fuels used by all Dutch passenger cars Source.
The high energy use is hardly surprising. Heating a building that’s entirely made of glass is very energy-intensive, because glass has a very limited insulation value. Each metre square of glass, even if it’s triple glazed, loses ten times as much heat as a wall.
Fruit Walls
The design of the modern greenhouse is strikingly different from its origins in the middle ages 1. Initially, the quest to produce warm-loving crops in temperate regions (and to extend the growing season of local crops) didn’t involve any glass at all. In 1561, Swiss botanist Conrad Gessner described the effect of sun-heated walls on the ripening of figs and currants, which mature faster than when they are planted further from the wall.
Gessner’s observation led to the emergence of the “fruit wall” in Northwestern Europe. By planting fruit trees close to a specially built wall with high thermal mass and southern exposure, a microclimate is created that allows the cultivation of Mediterranean fruits in temperate climates, such as those of Northern France, England, Belgium and the Netherlands.
An English fruit wall. Wikipedia Commons.
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The fruit wall reflects sunlight during the day, improving growing conditions. It also absorbs solar heat, which is slowly released during the night, preventing frost damage. Consequently, a warmer microclimate is created on the southern side of the wall for 24 hours per day.
Fruit walls also protect crops from cold, northern winds. Protruding roof tiles or wooden canopies often shielded the fruit trees from rain, hail and bird droppings. Sometimes, mats could be suspended from the walls in case of bad weather.
The use of available space was optimized by pruning the fruit trees.
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The fruit wall appears around the start of the so-called Little Ice Age, a period of exceptional cold in Europe that lasted from about 1550 to 1850. The French quickly started to refine the technology by pruning the branches of fruit trees in such ways that they could be attached to a wooden frame on the wall.
This practice, which is known as “espalier”, allowed them to optimize the use of available space and to further improve upon the growth conditions. The fruit trees were placed some distance from the wall to give sufficient space for the roots underground and to provide for good air ciculation and pest control above ground.
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Initially, fruit walls appeared in the gardens of the rich and powerful, such as in the palace of Versailles. However, some French...