THE LAZY GARDENER: The greenhouse goes west!

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Rob Foster, ‘The Lazy Gardener’, writes in Chad every month. Here he looks at the history greenhouses.

Horticulture was an established practice long before the dawn of recorded history including the art of manuring..

During the second century the idea was conceived of building an open house with concrete walls above the ground, and using it to grow plants inside. Initially the structure had no roof, but later it was covered with thin slabs of mica; sheet glass would not be discovered for another century.

Fires were kept burning around the outsides to keep the necessary temperatures inside. This type of building was called ‘specularium’.

Inside this, flowers and fruit were flourished. When the Roman Emperor Tiberius was ill, records tell us, he was ordered to eat cucumbers every day by his physicians, which he prepared from his ‘specularium’, much to the astonishment of his friends. As the Roman Empire fell their influence faded, and many of the horticultural methods were lost.

A Dominican friar by the name of Albertus Magnus, who was one of the great scholars of the time, wrote knowledgeably on the subject of plants.

Whilst studying, he delved into the writings of Roman horticulturists; consequently he revived the practice of forcing fruit and flowers in the hothouse. He was so successful that people became suspicious and charged him with witchcraft; he narrowly avoided death.

The next reference we have to the greenhouse is the ‘Physic’ garden, which was on the banks of the River Cherwell, near Magdelen College. The Earl of Danby donated the college, in 1621, for the purpose of ‘promoting the arts of horticulture’. Jacob Bobart, a head gardener from Germany, was employed to run it.

By 1637 the gardens catalogue showed some 1,600 species and varieties of plants were being grown. It was in this garden that a slate roofed greenhouse was built. It is very interesting to note from records that the house was heated by fire baskets burning charcoal. These were wheeled around the walls by gardeners! It was also in this garden that the first wooden greenhouse was erected in 1734.

The Apothecary Society started a garden in 1722 and this was designed to further the study of botany. This garden contained a greenhouse, Pepys writes of it has having ‘subterranean heat conveyed by a stove under the conservatory’.

By this time greenhouses were coming into more general use. The owners of large properties began erecting them. They soon became a status symbol, and to have two became a hallmark of wealth. It was not until the Great War that small-prefabricated greenhouses began to be made at prices suitable to the working man; even so they were still very expensive. Research still goes on into design, though the term glasshouse is used by professionals.

How does a Greenhouse heat up?

Short wave radiation from the sun easily passes through the glass, this will heat up the soil, benches, paths etc in the glasshouse, and these then re-radiate the heat as long waves that cannot pass through the glass so the glasshouse heats up. This will happen wherever the sun radiation passes through glass whether it is a sunny windowsill, or coldframe.

The Greenhouse goes west

Where do you site a greenhouse? Well, most of the time we do not have a choice if space is limited but if you can choose, select a site that is open and sunny, not shaded by trees or high walls. Build it as near to the house as possible so that it is convenient to install electricity, water etc. If you intend growing plants in it during the winter position it east to west, but if your main growing season is summer it is better running north to south. However avoid very exposed sites which are subject to strong north or easterly winds which will cause rapid heat loss.

How does it heat up?

Short wave radiation from the sun easily passes through the greenhouse glass. This will heat up the soil, benches, paths etc in the glasshouse, and these then re-radiate the heat as long waves that cannot pass through the glass.

Where do you site a greenhouse? If you can choose, select a site that is open and sunny, not shaded by trees or high walls. If you intend growing plants in it during the winter position it east to west, but if your main growing season is summer it is better running north to south.

However avoid very exposed sites which are subject to strong north or easterly winds which will cause rapid heat loss.