Walled garden

A pergola in the walled garden at
Hillsborough Park, Sheffield

A walled garden is specifically a garden enclosed by high walls for horticultural rather than security purposes, though traditionally all gardens have been hedged about or walled for protection from animal or human intruders. Garden walls may also serve a decorative purpose, but their essential function in the north temperate zone has been to shelter the garden from wind and frost.

The shelter of walling can raise the ambient temperature within the garden by several degrees, creating a microclimate that permits plants to be grown that would not survive in the unmodified local climate. Most walls were constructed from stone, but lining walls with brick, which absorbs and retains solar heat, raised the temperature against that 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.

A typical walled garden where the stone acts as a
slow-release reradiator of solar energy.

The traditional design of a walled garden, split into four quarters separated by paths, and a wellhead or pool at the centre, dates back to the very earliest gardens of Persia. The hortus conclusus or "enclosed garden" of High Medieval Europe was more typically enclosed by hedges or fencing, or the arcades of a cloister; though some protection from weather and effective protection from straying animals was afforded, these were not specifically walled gardens.

Movable blocks to control the movement of hot air in
 the heated wall at Eglinton Country Park.

British examples of elaborate walled gardens include Shugborough (England), Bodysgallen Hall (Wales),Alnwick Castle (England), Luton Hoo (England),Polesden Lacey (England), Myres Castle (Scotland) and Muchalls Castle (Scotland). In the United Kingdom, many country houses also had walled kitchen gardens, distinct from the decorative gardens. They received their greatest elaboration in the second half of the 19th century. Many of these labour-intensive gardens fell into disuse in the 20th century, but others have been revived to house primarily decorative gardens, some of which also produce fruit, vegetables and flowers for cutting.

A number of walled gardens in Britain have one hollow wall with openings in the stonework on the side facing towards the garden, so that fires could be lit inside the wall to provide additional heat to protect the fruit growing against the wall. Heat would escape into the garden through these openings, and the smoke from the fires would be directed upwards through chimneys or flues. This kind of hollow wall may be found at Croxteth Hall in Liverpool (England), and Eglinton Country Park and Dunmore House, both in (Scotland). In the 1800's the walls were lined with pipes and connected to a boiler, such work can be seen at Bank Hall in Bretherton.