Many historic gardens were formal in design, and geometry has been used in garden styles from the very earliest times. Persian and Egyptian gardens relied on a formal structure of hard landscape, often within a courtyard, in which planting, pergolas and water features would be laid out in a symmetrical pattern. The great Moorish gardens were largely formal, as were the sumptuous gardens of Renaissance Italy.

These gardens echoed the architectural styles of the day, and were designed to supply a strong visual connection between garden and house. In fact, any garden should do just that, but a formal style typically relies more heavily on the adjoining building for its inspiration. If the architecture of the house is classical, then formality in the garden should reflect this with features such as stone or gravel paths, parterres, stone paving, balustrading, formal pools, clipped hedging and framed views.

Of course, a building does not need to be classical to have an adjoining formal garden, but it does need to be a building with some character of its own. In this way, a formal garden could suit a Georgian house or a Victorian villa, but it could also suit a modern architect-designed building, reflecting the regularity of the house and providing a harmonious link between the inside and outside. However, a formal garden is less likely to work well with a pre-war semi or a developer's house on a modern estate. These tend not to have a balanced facade or strong layout, so an asymmetrical design would probably look, and certainly feel, more comfortable in these cases.

A feeling of formality may be achieved by creating classicism and symmetry in simple ways: by planting two or a number of symmetrically placed trees; by placing pots or urns on either side of a gateway; or perhaps by positioning clipped shrubs to flank a front door.

Such a strictly architectural style requires that plants be used to emphasise and embellish rather than dominate. Hedging, which can be close clipped, is the often one of the most important features of the formal garden. Many hedges are made from clipped and severely restricted trees, for example, limes can be 'pleached' to make a narrow hedge on clear trunks or 'stilts'. Fruit trees, carefully pruned for the purpose, can also be used to form linear barriers, and window-like holes can be even be carved into these hedges to create clairvoyees.

Formal gardens rely heavily on surfaces for much of their impact, and the lawn is important for this reason. Colours are often muted in the formal garden, with green predominating, and the lawn acts as a subtle foil to other shades of green, such as the black-green of yew.

Strictly speaking, plants should not be allowed to spill over on to hedges and paths, or otherwise break up the strict architectural lines of the garden. However, some gardeners bend the rules and plant informally within the formal framework. This often involves planting drifts of flowers in the borders, and using a larger range of plant material than would be strictly appropriate for the traditional formal garden. This method of planting undoubtedly softens the impact of the formal lines, but that loss is often compensated by the splendour of the plants.