Good looking gardens are designed around several design principles; these include such things as; rhythm, unity, repetition, balance, proportion, simplicity and focal points.
Of all of the garden design principles unity is probably the most important principle to apply and one of the hardest to describe, but when it is present you know because your eyes and brain are pleased to see it.
When you look at a garden, on an unconscious level your mind simplifies and organises what it sees, it looks for a connection between the elements, for some sort of organisation, for a common thread that runs through your garden.
A unified design creates a harmony between the various elements so that they relate to each other, work well together and create an impact.

Unity of Themes
Where a garden has a theme which overrides everything else.
For example, a Japanese Garden, which relies on precise, strong sculptural forms and texture such as rocks, gravel and planting.
Or, as seen in the gardens of Sissinghurst, Kent(right) and Hidcote Manor, Gloucestershire, designed and laid out by Vita Sacksville-West and Lawrence Johnston respectively, both have strong overriding geometric layouts that create a series of interlocking out-door rooms seperated by hedges and paths.
Hidcote Manor, Gloucestershire
Or in a water garden.
RHS Gold Medal ‘Huckleberry’s Hideout’, in which it’s overriding theme naturally unifies the design.
Unity of Style
The style of a garden is defined by the geometry used in the design. The style may be formal, asymmetrical or informal.
Formal style
In a formal design the style is symmetrical, usually across a central axis, and creates a static, calm and restful feel to a garden. Such as those in the Moorish gardens of the Alhambra Palace in Granada, Andalusia, Spain.
Asymmetrical style
An asymmetrical style falls somewhere between informal and formal.
Asymmetry was an important tool for the Modernists of the 1930’s, were the cross over off ideas between garden designers such as, Thomas Church and Garrett Eckbo and artists was apparent in the paintings of Mondrian whose beautiful geometric patterns can be perfectly translated into garden designs.
Informal Style
A more fluid, organic style which relies on curves to create free flowing informal patterns.
The landscape architect Roberto Burle Marx was the master of the informal style in his paintings and landscapes.

Japanese Gardens are also good examples of the informal pattern.
Designed with careful balance and proportions and created around philosophy they contain precisely placed traditional elements such as stones, rocks and plants with dynamic form and textures.
Unity of Detail
Visual unity can be achieved in repeating similar elements such as plants, to create a harmony within the garden design.
This can be seen in the ‘White Garden’ at Sissinghurst.
Unity of the landscape and location
Look too at the architecture of your house, the material used to build it or, the views of the landscape beyond all can be used to unify your garden design. Use whatever colours, shapes and forms you see around you and repeat them. Even the most unpromising prospects can be used to good effect.
Dungeness B nuclear power station in Kent.
Against this backdrop, with ranks of pylons and the bleak expanse of shingle stretching into the distance, the garden of the artist and film director, Derek Jarman, mimics with tall, upright pieces of driftwood, the pylons on the horizon.
Just as a garden design that has too much variety appears busy and confused, too much unity is boring. The garden designer’s job is to find that perfect balance between the two.