Walled garden

A walled garden is a garden enclosed by high walls for horticultural rather than security purposes, although originally all gardens may have been enclosed for protection from animal or human intruders. In temperate climates, the essential function of the walls surrounding a walled garden is to shelter the garden from wind and frost, though they may also serve a decorative purpose.

The shelter provided by enclosing walls can raise the ambient temperature within a garden by several degrees, creating a microclimate that permits plants to be grown that would not survive in the unmodified local climate.

Most walls are constructed from stone or brick, which absorb and retain solar heat and then slowly release it, raising the temperature against the wall, allowing peaches, nectarines, and grapes to be grown as espaliers against south-facing walls as far north as southeast Great Britain and southern Ireland.

The ability of a well-designed walled garden to create widely varying stable environments is illustrated by this description of the rock garden in the Jardin des Plantes in Paris’ 5ème arrondissement, where over 2,000 species from a variety of climate zones ranging from mountainous to Mediterranean are grown within a few acres:

The garden is protected from sudden changes in weather conditions and from harsh winds, thanks to its hollowed out terraces and the big trees …. The gardeners make the most of the northern or southern exposures and the permanently shady areas of this little, sheltered valley. Within just a few metres, temperatures can range from 15 to 20 degrees C, what one would call a micro-climate!

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Wikipedia