Balance is a principle of all art forms, design, and even landscape design. It implies a sense of equality. And while there may be just a little more to it, this is how I explain it to make it easier for first timers and do it yourselfers to understand.
A garden, landscape, or any form of equal proportions would naturally feel and look balanced. However, most gardens and landscapes are not exact or symmetrical in shape and form. They’re asymmetrical and abstract in form and are often without any natural balance of their own. So landscaping often relies on other elements to create balance and harmony through unity.
Many times, a lack of balance is directly related to a lack of repetition. Repeating alike elements such as plants or rocks throughout the landscape will help unify different areas to each other. As little as one repeated matching plant group, color, piece of decor, or hardscape can accomplish this.
A lack of balance is also created by placing too many or all non matching elements throughout a landscape design. This can sometimes seem cluttered and unkept when it grows in. In the beginning of your design, plan for less, place just a few matching plant groups throughout the garden, and keep decor matching and to a minimum. You can add more later.