Hot Walls for Grapes

It is the finest garden I have ever seen about this town,
and abundance of hot walls for grapes,
where they are in great plenty, and ripening fast.


Jonathan Swift
Letter to Stella
1 September 1711

So wrote Jonathan Swift in a letter to his friend, Stella, in reality, a young lady named Esther Johnson. This letter was written after a visit to the extensive gardens surrounding the country house of his friend, Lord Peterborough, at Parsons Green, near Windsor. Lord Peterborough was away at the time, but his secretary had given the Reverend Swift a tour of the grounds of Peterborough’s estate, followed by a fine dinner.

Just what were "hot walls for grapes," and were they still in use during the Regency?

Archaeological excavations have shown some evidence that grapes may have been grown in Britain in pre-historic times. However, it was not until the time of the Roman occupation that there is reliable evidence of viticulture, the cultivation of grapes, in southern England. The Romans probably introduced their own strains of grapes, rather than cultivating indigenous varieties. Amphorae and other vessels which indicate the drinking of wine have been found in the excavations of nearly every Roman settlement in Britain. When the Angles and Saxons invaded the British Isles, the cultivation of grapes was almost completely neglected, as those peoples preferred beer and mead to wine. As early Christianity spread across Britain, grapes began to be cultivated again, usually at monasteries, since wine was necessary to various Christian rituals and ceremonies. In the following centuries, Viking invasions, which often focused on monasteries for their wealth, severely damaged many vineyards associated with the monasteries.

William the Conqueror and his Normans brought both an inborn taste for wine and their extensive skill at viticulture and wine-making to England when they vanquished the Saxons. Meteorological historians have shown that the climate in England during the Middle Ages, a period known as the Medieval Warm Period, was warm enough to sustain the cultivation of grapes as far north as York. Once again, many monasteries began to cultivate grapes and make wine. In addition, so did a number of nobles with large estates, particularly those located in southern England. Viticulture was extremely labor-intensive and a number of vineyards became neglected as the Black Death took more and more of the laborers needed to care for the vines. The most devastating blow to the widespread cultivation of grapes in England, which was once again centered in the monasteries, came when Henry VIII broke with the Church of Rome and then dissolved the monasteries in England.

Though a few major landowners continued to cultivate grapes after the dissolution of the monasteries, the onset of the Little Ice Age made that increasingly difficult. As the cold advanced over the British Isles, viticulture was forced further and further south. By the turn of the seventeenth century, grapes were only able to thrive in the southern third of the country. As the years passed, summers continued to become shorter and cooler, even in southern England. In order to fully ripen, most varieties of grapes need a long, warm summer which extends into the fall. Regardless of the cooling climate, a number of the larger landowners were determined to continue to cultivate grapes. And before the century was out, a solution was found.

The solution came to be known as "hot walls," and was probably developed by an experienced gardener, though he, or she, remains unknown. Nor is anyone certain when or where this concept of heated walls was first introduced. But by the end of the century, a number of estates, mostly in southern England, had kitchen gardens encircled by walls which could be heated to provide the growing grapes with the extended warmth they needed to fully ripen for harvesting, typically in mid to late October. These garden walls were usually built of brick and on the inside of the walls, running along the length of every third or fourth course was a hollow tube, usually of clay, of perhaps an inch in diameter. At the base of the wall, about every eight to ten feet, cut into the wall, was essentially a small fireplace, each with a vertical chimney above it which rose up the height of the wall, intersecting with each horizontal tube.

The grape vines would be planted near the base of the walls, and trained to grow up them. During the summer, the walls themselves would usually absorb enough heat from the sun to help keep the grapes warm enough to grow. But once the fall came, the days became shorter and cooler. Without additional warmth, the partially mature grapes would not be able to fully ripen. It was at this time that small fires of hot-burning wood would be lit in each of the fireplace openings at the base of the wall. The hot air would rise up the vertical chimneys and flow through the horizontal tubes built into the surface of the wall. The bricks of the wall would absorb this heat, providing the grapes with the warmth they needed to fully ripen. The walls would be kept heated until the second or third week of October, when the grapes would usually be ready to be picked.

Not all grapes were used for making wine. Many were grown simply for eating, as they were a popular fruit for the dessert course, right through the Regency. Grapes were also grown to make both vinegar and verjuice, which were used in cooking, as condiments and/or for some medicinal preparations. Large estates, such as Lord Peterborough’s, which Jonathan Swift toured, typically had very large kitchen gardens, encircled with extensive hot walls, against which many grape vines could be grown. With such a large volume of grapes, wine could be made on those estates, if the owner was so inclined. On smaller estates, kitchen gardens were smaller, with more limited hot walls. In these gardens, grapes would still be grown, but these were typically harvested for eating and for making a limited amount of vinegar and/or verjuice.

Hot garden walls did not only extend the growing season for grapes. Other fruits or vegetables could be planted near the walls to take advantage of the warmth they radiated in order to ensure they would fully mature each growing season. For many plants, the main need was to prevent frost during early fall nights. Of course, to accomplish this, someone would have to remain in the garden overnight to tend the fires which heated the walls. On larger estates, this task would usually fall to the lowest gardener’s assistant. In smaller gardens, the task may have been assigned to one of the lesser servants in the household. These hot walls were not inexpensive to build, nor were they cheap to heat, or to manage. But many households considered them well worth the cost since they ensured a better yield of fruits and vegetables from their kitchen gardens each year, regardless of the weather conditions.

During the eighteenth century, hot garden walls were built on a number of estates, both large and small, across England and in Ireland. There were even a number built in the American colonies. However, there do not seem to have been any hot walls built in Scotland, which was too far north to support viticulture. Many of these heated walls were still in use during the Regency, though some had been allowed to fall into disrepair. Fewer hot walls were built in the nineteenth century, as more property owners preferred greenhouses. However, not many varieties of grapes do well in greenhouses, they need direct sun to properly ripen. But fewer landowners in Britain were making wine by the nineteenth century and grapes could be more easily imported, so there was much less need for hot garden walls. The majority of them were no longer used and eventually many of them were demolished as old-fashioned and unnecessary.

However, there are still a few hot garden walls to be found on estates in England and in Ireland, though not many people today realize what they are or how they were used in times past. Should you visit a country estate in England or Ireland which has a walled garden, take a close look at the inside of the walls for the tell-tale features of a built-in heating system. Are there small openings at the base of the wall every eight to ten feet? Are there raised ridges running horizontally along the walls, twelve to eighteen inches apart? If those features are present, you are looking at a wall which was once heated to ensure the successful maturation of grape vines and other fruit-bearing plants for the family who lived on that estate.

Might a heated garden wall figure in a Regency romance? Perhaps a young lady living on a small estate in the country helps support her family by making special vinegars and verjuice which she sells in the local village, or even to a specialty shop in London. Fortunately, her grandfather had an extensive hot wall built around their kitchen garden, which she has repaired and uses to cultivate grape vines. Perhaps the vines were already in the garden, just neglected, or she got cuttings from a friend or maybe the gardener on a larger, neighboring estate who wishes to help her. Mayhap the hero, fleeing the villain who has seriously wounded him, stumbles upon a kitchen garden with hot walls on a cold fall evening. A secluded corner of that garden provides him with a warm place to hide, but he falls asleep and is found by the person who is tending the fires in the wall for the night. Possibly the same young lady who is growing those grapes to help support her family? Or, if the hot wall is not in use, there are all those hollow tubes running along its inside surface. Might one of them be just the place to hide something small and valuable? Dear Regency Authors, could a hot wall heat up one of your stories?

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About Kathryn Kane

Historian with a particular interest the English Regency era.   An avid reader of novels set in that time, holding strong opinions on the historical accuracy to be found in said novels.
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5 Responses to Hot Walls for Grapes

  1. kwillow says:

    I can imagine a “poor relation” heroine of a wealthy landowner using hot walls to grow beautiful orchids and other exotic flowers to sell to local fashionable ladies. Book could be called “The Flower Girl”.

    • Kathryn Kane says:

      I like the idea, and the title. However, the story will have to be set in the Victorian era, since orchids did not get their name until 1845. But if the story is set in the Regency, perhaps she could grow rare roses, which were very popular at that time because the Empress Josephine cultivated hundreds of different varieties of them at Malmaison.

      Regards,
      Kat

  2. KH_Tas says:

    There’s an intact hot wall (which sounds to be of a slightly different design) in the Royal Botanic Gardens in Hobart, Australia, built before Europeans realised that the Australian climate was warm enough on its own.

    • Kathryn Kane says:

      That is very interesting. The English, in particular, are so traditional. How like them to build a hot wall before they knew if they actually needed one! 😉

      There are slightly different design and construction techniques used in each of the few hot walls I have seen. Which is not surprising, since from what I can tell, it was the basic concept which circulated around Britain. Each landowner and/or his/her gardener then built the hot wall with only the idea as their guide. There were no standard plans of which I am aware.

      Thanks for taking the time to share your knowledge. I was not even aware that Tasmania had a Botanic Gardens until you posted your comment.

      Regards,

      Kat

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