“Fruit walls in Montreuil, a suburb of Paris”

Fruit Walls: Urban Farming in the 1600s
by Kris De Decker / 12/2015

“We are being told to eat local and seasonal food, either because other crops have been transported 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 p15] This makes greenhouse-grown crops as energy-intensive as pork meat (40-45 MJ/kg in the USA). [Source]

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.’

“Dutch-style all-glass greenhouses”

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”

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 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.

Peach Walls in Paris
Initially, fruit walls appeared in the gardens of the rich and powerful, such as in the palace of Versailles. 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.

Established during the seventeenth century, Montreuil had more than 600 km fruit walls in the 1870s, when the industry reached its peak. The 300 hectare maze of jumbled up walls was so confusing for outsiders that the Prussian army went around Montreuil during the siege of Paris in 1870.

Peaches are native to France’s Mediterranean regions, but Montreuil produced up to 17 million fruits per year, renowned for their quality. Building many fruit walls close to each other further boosted the effectiveness of the technology, because more heat was trapped and wind was kept out almost completely.

Within the walled orchards, temperatures were typically 8 to 12°C (14-22°) higher than outside. The 2.5 to 3 metre high walls were more than half a metre thick and coated in limestone plaster. Mats could be pulled down to insulate the fruits on very cold nights. In the central part of the gardens, crops were grown that tolerated lower temperatures, such as apples, pears, raspberries, vegetables and flowers.

Grapes in Thomery
In 1730, a similar industry was set up for the cultivation of grapes in Thomery, which lies some 60 km south-east from Paris — a very northern area to grow these fruits. At the production peak in the early twentieth century, more than 800 tonnes of grapes were produced on some 300 km of fruit walls, packed together on 150 hectares of land.

The walls, built of clay with a cap of thatch, were 3 metres high and up to 100 metres long, spaced apart 9 to 10 metres. They were all finished by tile copings and some had a small glass canopy. Because vines demand a dry and warm climate, most fruit walls had a southeastern exposure. A southern exposure would have been the warmest, but in that case the vines would have been exposed to the damp winds and rains coming from the southwest. The western and southwestern walls were used to produce grapes from lower qualities.

“The town of Thomery today, seen through Google maps. The old fruit walls are still dominating the landscape. The houses were built later.”

Some cultivators in Thomery also constructed “counter-espaliers”, which were lesser walls opposite the principal fruit walls. These were only 1 metre high and were placed about 1 to 2.5 metres from the fruit wall, further improving the microclimate. In the 1840s, Thomery became known for its advanced techniques to prune the grape vines and attach them to the walls. The craft spread to Montreuil and to other countries.

Storage system for grapes in Thomery.”

The cultivators of Thomery also developed a remarkable storage system for grapes. The stem was submerged in water-filled bottles, which were stored in large wooden racks in basements or attics of buildings. Some of these storage places had up to 40,000 bottles each holding one or two bunches of grapes. The storage system allowed the grapes to remain fresh for up to six months.

“A Serpentine Fruit Wall in the Netherlands” 

Serpentine Fruit Walls
Fruit wall industries in the Low Countries (present-day Belgium and the Netherlands) were also aimed at producing grapes. From the 1850s onwards, Hoeilaart (nearby Brussels) and the Westland (the region which is now Holland’s largest glasshouse industry) became important producers of table grapes. By 1881, the Westland had 178 km of fruit walls.

The Dutch also contributed to the development of the fruit wall. They started building fruit walls already during the first half of the eighteenth century, initially only in gardens of castles and country houses. Many of these had unique forms. Most remarkable was the serpentine or “crinkle crankle” wall. Although it’s actually longer than a linear wall, a serpentine wall economizes on materials because the wall can be made strong enough with just one brick thin.

The alternate convex and concave curves in the wall provide stability and help to resist lateral forces. Furthermore, the slopes give a warmer microclimate than a flat wall. This was obviously important for the Dutch, who are almost 400 km north of Paris. Variants of the serpentine wall had recessed and protruding parts with more angular forms. Few of these seem to have been built outside the Netherlands, with the exception of those erected by the Dutch in the eastern parts of England (two thirds of them in Suffolk county). In their own country, the Dutch built fruit walls as high up north as Groningen (53°N).

“Fruit walls improved, Nicolas Fatio de Duilier, 1699”

Another variation on the linear fruit wall was the sloped wall. It was designed by Swiss mathematician Nicolas Fatio de Duillier, and described in his 1699 book “Fruit Walls Improved”. A wall built at an incline of 45 degrees from the northerm horizon and facing south absorbs the sun’s energy for a longer part of the day, increasing plant growth.

“A heated fruit wall of Croxteth Hall Walled Kitchen Garden in Liverpoool”

Heated Fruit Walls
In Britain, no large-scale urban farming industries appeared, but the fruit wall became a standard feature of the country house garden from the 1600s onwards. The English developed heated fruit walls in the eighteenth and nineteenth centuries, to ensure that the fruits were not killed by frost and to assist in ripening fruit and maturing wood. In these “hot walls”, horizontal flues were running to and fro, opening into chimneys on top of the wall.

Initially, the hollow walls were heated by fires lit inside, or by small furnaces located at the back of the wall. During the second half of the nineteenth century, more and more heated fruit walls were warmed by hot water pipes. The decline of the European fruit wall started in the late nineteenth century. Maintaining a fruit wall was a labour-intensive work that required a lot of craftsmanship in pruning, thinning, removing leaves, etcetera. The extension of the railways favoured the import of produce from the south, which was less labour-intensive and thus cheaper to produce. Artificially heated glasshouses could also produce similar or larger yields with much less skilled labour involved.

The Birth of the Greenhouse
Large transparant glass plates were hard to come by during the Middle Ages and early modern period, which limited the use of the greenhouse effect for growing crops. Window panes were usually made of hand-blown plate glass, which could only be produced in small dimensions. To make a large glass plate, the small pieces were combined by placing them in rods or glazing bars.

Nevertheless, European growers made use of small-scale greenhouse methods since the early 1600s. The simplest forms of greenhouses were the “cloche”, a bell-shaped jar or bottomless glass jug that was placed on top of the plants, and the cold- or hotframe, a small seedbed enclosed in a glass-topped box. In the hotframe, decomposing horse manure was added for additional heating.

In the 1800s, some Belgian and Dutch cultivators started experimenting with the placement of glass plates against fruit walls, and discovered that this could further boost crop growth. This method gradually developed into the greenhouse, built against a fruit wall. In the Dutch Westland region, the first of these greenhouses were built around 1850.

By 1881, some 22 km of the 178 km of fruit walls in the westland was under glass. These greenhouse structures became larger and more sophisticated over time, but they all kept benefitting from the thermal mass of the fruit wall, which stored heat from the sun for use at night. In addition, many of these structures were provided with insulating mats that could be rolled out over the glass cover at night or during cold, cloudy weather. In short, the early greenhouse was a passive solar building.

“Dutch greenhouse from the 1930s, built against a brick wall”

The first all glass greenhouses were built only in the 1890s, first in Belgium, and shortly afterwards in the Netherlands. Two trends played into the hands of the fully glazed greenhouse. The first was the invention of the plate glass production method, which made larger window panes much more affordable.

“Greenhouse built against a serpentine fruit wall” 

The second was the advance of fossil fuels, which made it possible to keep a glass building warm in spite of the large heat losses. Consequently, at the start of the twentieth century, the greenhouse became a structure without thermal mass. The fruit wall that had started it all, was now gone.

During the oil crises of the 1970s, there was a renewed interest in the passive solar greenhouse. However, the attention quickly faded when energy prices came down, and the fully glazed greenhouse remained the horticultural workhorse of the Northwestern world. The Chinese, however, built 800,000 hectare of passive solar greenhouses during the last three decades — that’s 80 times the surface area of all glass greenhouses in the Netherlands.”

Sources and more information:
Open Air Grape Culture, John Phin, 1862
The last peach orchards of Paris, Messy Nessy, 2014
Geschiedenis van het leifruit in de Lage Landen, Wybe Kuitert, 2004
Onzichtbaar achter glas, Ahmed Benseddik and Marijke Bijl, 2004
Chasselas de Thomery, French Wikipedia
Murs à pêches, French Wikipedia
L’histoire des murs, website Murs à Pêches
Food-Producing Solar Greenhouses, in “An assessment of technology for local development”, 1980
The development and history of horticulture, Edwinna von Bayer
Geschiedenis van Holland, Volume 3, deel 1. Thimo de Nijs, 2003
A Golden Thread: 2500 years of solar architecture and technology, Ken Butti and John Perlin, 2009<
Une histoire des serres: de l’orangerie au palais de cristal, Yves-Marie Allain, 2010
Manual complet du jardinier, Louis Claude Noisette, 1862
Onderhoud en restauratie van historische plantenkassen, Ben Kooij, 2011
Leifruit: toekomst voor eeuwenoude hovernierskunst, Julia Voskuil, 2011
The magic of Britain’s walled gardens, Bunny Guinness, 2014
Visiting the palace of Versailles’ kitchen garden, Janet Eastman, 2015
Hot Walls: An Investigation of Their Construction in Some Northern Kitchen Gardens, Elisabeth Hall, 1989
– History of fruit growing, Tom La Dell
– Fences of Fruit Trees, Brian Kaller, 2011

  1. The greenhouse was invented by the Romans in the second century AD. Unfortunately, the technology disappeared when the Western Roman Empire collapsed. The Romans could produce large glass plates, and built greenhouses against brick walls. Their technology was only surpassed by the Dutch in the 1800s. However, the Roman greenhouse remained a toy for the rich and never became an important food supply. The Chinese and Koreans also built greenhouses before or during the middle ages. Oiled paper was used as a transparant cover. All of these greenhouses had thick walls to retain the heat from the sun and/or a radiant heating system (such as the Chinese Kang or the Korean ondol). 

“A Chinese greenhouse”

by Kris De Decker / 12/2015

“The modern glass greenhouse requires massive inputs of energy to grow crops out of season. That’s because each square metre of glass, even if it’s triple glazed, loses ten times as much heat as a wall. However, growing fruits and vegetables out of season can also happen in a sustainable way, using the energy from the sun. Contrary to its fully glazed counterpart, a passive solar greenhouse is designed to retain as much warmth as possible. Research shows that it’s possible to grow warmth-loving crops all year round with solar energy alone, even if it’s freezing outside. The solar greenhouse is especially successful in China, where many thousands of these structures have been built during the last decades. The quest to produce warm-loving crops in temperate regions initially didn’t involve any glass at all.

In Northwestern Europe, Mediterranean crops were planted close to specially built “fruit walls” with high thermal mass, creating a microclimate that could be 8 to 12°C (14 to 22°F) warmer than an unaltered climate. Later, greenhouses built against these 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.

During the oil crises of the 1970s, there was a renewed interest in the passive solar greenhouse. 6  However, the attention quickly faded when energy prices came down again, and the all-glass greenhouse remained the horticultural workhorse of the Northwestern world. The Chinese, on the other hand, built 800,000 hectare of passive solar greenhouses during the last three decades — that’s 80 times the surface area of the largest glasshouse industry in the world, that of the Netherlands.

“A Chinese greenhouse”

The Chinese Solar Greenhouse
The Chinese passive solar greenhouse has three walls of brick or clay. Only the southern side of the building consists of transparant material (usually plastic foil) through which the sun can shine. During the day the greenhouse captures heat from the sun in the thermal mass of the walls, which is released at night. At sunset, an insulating sheet — made of straw, pressed grass or canvas — is rolled out over the plastic, increasing the isolating capacity of the structure. The walls also block the cold, northern winds, which would otherwise speed up the heat loss of the greenhouse.

“Chinese greenhouses”

Being the opposite of the energy-intensive glass greenhouse, the Chinese passive solar greenhouse is heated all-year round with solar energy alone, even when the outdoor temperature drops below freezing point. The indoor temperature of the structure can be up to 25°C (45°F) higher than the outdoor temperature. The incentive policy of the Chinese government has made the solar greenhouse a cornerstone of food production in central and northern China. One fifth of the total area of greenhouses in China is now a solar greenhouse. By 2020, they are expected to take up at least 1.5 million hectares. 1

Improving the Chinese Solar Greenhouse
The first Chinese-style greenhouse was built in 1978. However, the technology only took off during the 1980s, following the arrival of transparent plastic foil. Not only is foil cheaper than glass, it is also lighter and doesn’t require a strong carrying capacity, which makes the construction of the structure much cheaper. Since then, the design has continuously been improved upon. The structure became deeper and taller, allowing sunlight to be distributed better and ensuring that temperature fluctuations are decreased.

In addition, cultivators are increasingly opting for modern insulation materials instead of using rammed earth or air cavities for the insulation of the walls, which saves space and/or improves the heat absorption characteristics of the structure. Synthetic insulation blankets, which are better suited for dealing with moisture, are also seeing increased use. The old-fashioned straw mats become heavier and insulate less when they become wet.

A: The original design from the 1980s with a glass canopy. B: An improved design from the mid-1980s, with plastic foil, a night curtain, and better insulated walls. This design is the most widespread. C: An improved design from 1995. The walls are thinner because they are insulated with modern materials. Automatic handling of the night curtain. D: The most recent design from 2007, which has a double roof for extra insulation.”

In some of the more recent greenhouses, the insulation blankets are rolled up and down automatically, and more sophisticated ventilation systems are used. Some greenhouses have a double roof or reflecting insulation installed. In addition, the plastic foil used for the greenhouses — obviously the least sustainable component of the system — is continuously being improved, resulting in a longer lifespan.

The performance of the Chinese greenhouse depends on its design, the latitude, and the local climate. A recent study observed three types of greenhouses in Shenyang, the capital of the Liaoning province. The city is at 41.8°N and is one of the most northern areas where the Chinese-style greenhouse is built (between latitudes 32°N and 43°N). The research was conducted from the beginning of November to the end of March, the period during which the outside temperature drops below freezing. The average temperature in the coldest month is between -15°C and -18°C (5 to -0.4°F). 1

“Air cavities in a ruined solar greenhouse”

The three greenhouses studied all have the same shape and dimensions (60 x 12.6 x 5.5 m), but the walls, the plastic foil, and the transparent layer vary. The simplest construction has walls of rammed earth and an inside layer of brick to increase the structures’ stability. The covering is a thin plastic film that is covered at night with a straw blanket. The two other greenhouses have a northern wall of brick with extruded polystyrene foam as insulating material, whereby the width of the wall can be cut in half. They are also covered with a thicker PVC plastic foil. The best greenhouse adds to this a reflective coating on the insulation blanket, further reducing heat loss at night.

“The night curtain of a solar greenhouse”

In the simplest greenhouse the temperatures dropped below the freezing point from early December until mid-January. Without extra heating, this greenhouse cannot grow any produce at this latitude. Only the most sophisticated greenhouse – with its reflecting insulation layer – succeeded in keeping the inside temperature above freezing at all times, using only solar energy. What’s more, the temperature stayed above 10°C most of the time, which is the minimum temperature for the cultivation of warm season plants, like tomatoes and cucumbers. Of course, passive solar greenhouses in more southern locations would require less sophisticated insulation techniques to be operated without additional heating.

Solar Greenhouses in Northern Climates
If we go further north, similar solar passive greenhouses would require extra heating during the coldest months of the year, no matter how well they are insulated. Note that the farther north the greenhouse is located, the greater its slope will be. The slope of the roof is angled to be perpendicular to the sun’s rays when it’s lowest on the horizon. In 2005, a Chinese-style greenhouse was tested in Manitoba, Canada, at a latitude of 50°N. A greenhouse that is 30 x 7 meters with a well-insulated northern wall (3.6 RSI glass fibre) and an insulation blanket (1.2 RSI cotton) was observed from January to April. During the coldest month (February) the outside temperature varied between +4.5°C and -29°C (40 to -20°F). While the interior temperature was on average 18°C (32.4°F) higher than the exterior, it turned out to be impossible to cultivate plants without extra heating during the winter. 2

“Strawberries in a Chinese solar greenhouse”

Nevertheless, energy savings can be huge in comparison to a glass greenhouse. To keep the temperature above ten degrees at all times, the heating system of the Canadian structure must deliver a maximum of 17 W/m2, or 3.6kW for the building. 2 In comparison, a glass greenhouse of equal proportions at the same interior and exterior temperatures would require a maximum capacity of 125 to 155 kW.

Note that these results can’t be applied to all locations at 50°N. The Canadian research shows that solar output has a greater impact on the inside temperature of the structure than does the outside temperature. The correlation between inside temperature and sunlight is almost four times greater than the correlation between inside temperature and outside temperature. 2

For example, while Brussels lies at the same latitude as Manitoba, the latter has on average 1.5 times more sun. Thermal capacity can be further improved by placing black painted water storage tanks against the north wall inside the structure. These capture extra solar energy during the day and release it during the night. A different method to improve the heat retention of a greenhouse is by earth berming the north, east and west walls. Yet another solution to improve insulation is the underground or “pit greenhouse”. 7 However, this greenhouse receives less sunlight and is prone to flooding.

“Cucumbers in a Chinese solar greenhouse”

More Space Needed
The passive greenhouse could save a lot of energy, but a price would have to be paid: the profits generated by the Chinese greenhouse are two to three times lower per square meter than those of its fully glazed counterpart. In the more efficient Chinese greenhouses, an average 30 kg of tomatoes and 30 kg of cucumbers can be grown per square meter (numbers from 2005), while the average production in a glass greenhouses is about 60 kg of tomatoes and 100 kg cucumbers (numbers from 2003). 3,4

A passive greenhouse industry would thus take up two to three times as much space to produce the same amount of food. This could be viewed as a problem, but of course what really eats space in agriculture is meat production. A more diverse and attractive supply of vegetables and fruits could make it more viable to reduce meat consumption, so land use shouldn’t be a problem.

“A Chinese solar greenhouse”

Compost Heated Greenhouses
Another issue with a solar powered greenhouse is the lack of a CO2-source. In modern greenhouses, operators aim to have a CO2-level at least three times the level outdoors to increase crop yield. This CO2 is produced as a byproduct of the fossil fuel based heating systems inside the greenhouses. However, when no fossil fuels are used, another source of CO2 has to be found. This is not only an issue for solar greenhouses. It’s also one of the main reasons why geothermal energy and electric heat pumps are not advancing in the modern glasshouse industry.

In Chinese solar greenhouses, this issue is sometimes solved by the combined raising of produce and animals. Pigs, chickens, and fish all produce CO2 that can be absorbed by the plants, while the plants produce oxygen (and green waste) for the animals. The animals and their manure also contribute to the heating of the structure. Research of such integrated greenhouse systems has shown that the combined production of vegetables, meat, milk, and eggs raises yields quite substantially. [^5]

“Detail of a compost-heated greenhouse”

Justin Walker, an American now living in Siberia, is building an integrated system using horses, goats and sheep in a monastery in Siberia. Considering the harsh climate, the structure is partly built below-ground, while its protruding parts are earth-bermed. Above the barn area is a hayloft that provides further winter insulation as well as ventilation in the summer when it is empty. His compost heat recovery system produces hot water that is piped through radiant floor heating zones in the floor of the greenhouse. The CO2 is supplied by the animals. 5

Heating and CO2-production can also be done without housing animals in the greenhouse. Their manure suffices. As we have seen in the previous article, the use of horse manure for heating small-scale greenhouses dates back several centuries in Europe, and in China it was practised already 2.000 years ago.

Since the 1980s, several compost heated greenhouse have been built in the USA. These have shown that a greenhouse can be entirely heated by compost if it is well-insulated, and that the method drastically enriches the CO2-levels in the soil and in the greenhouse air. To add to this, the compost also serves to increase soil fertility.” 5

  1. Energy performance optimization of typical chinese solar greenhouses by means of dynamic simulation, Alessandro Deiana et al., International conference of agricultural engineering, 2014, Zurich. 
  2. Winter performance of a solar energy greenhouse in southern Manitoba, Canadian Biosystems Engineering. 2006. 
  3. The solar greenhouse: state of the art in energy saving and sustainable energy supply. G. Bot et al., 2005 
  4. Structure, function, application, and ecological benefit of a single-slope, energy-efficient solar greenhouse in China. HortTechnology, June 2010 Integrated energy self-served animal and plant complementary ecosystem in China, in “Integrated energy systems in China — the cold northwestern region experience”, FAO, 1994 
  5. The Compost-Powered Water Heater: How to heat your greenhouse, pool, or buildings with only compost, Gaelan Brown, 2014 
  6. See for example The Solar Greenhouse Book, published by Rodale Press in 1978 
  7. The Earth Sheltered Solar Greenhouse Book, Mike Oehler, 2007