Unity in the landscape can be achieved through a theme of colors, forms, or textures without using exactly the same plants. For example, a red color may be used as a theme, but you could use plants with reddish foliage as well as other plants with similar colored flowers or foliage. The plants would be in different areas of the landscape, but the color theme unites the overall landscape. Other themes, such as kinds of plants, curves or straight lines, and construction materials, can be used to create unity in the design. Too many design themes can be confusing, however, and unity of design lost, so you need to keep the design simple.
Simplicity is an important principle of design, but it is a hard one to achieve.
Too many different colors, textures, and forms result in visual confusion, and any sense of design can be ruined. One way to achieve simplicity is by using a limited range of plant species. On the other hand, you need to provide some variety in the landscape. Don't use the same kind of plant everywhere. A long hedge of the same kind of plant can be very monotonous, for example.