Many people just entering the complicated world of gardening focus on one thing; flowers. They love them, and plant lots of colorful perennials together to create their dream garden; and yet, when it comes to fruition, they feel like something has fallen short ..... it just doesn't pop. It looks too jumbled, too boring.
The likely problem is that they focused too much on the flowers and not enough on the other elements needed to create an artistic composition. A truly beautiful garden has a combination of mixed elements; flowering plants being the least important. Structural plants, like trees and shrubs, should be considered first along with stone outcroppings, walls, fences and other massing elements. Negative space ( like lawn, walkways, patios, and gravel areas ) is also important. An entire front yard filled with plants and no place for the eye to rest, is overwhelming to the senses. Just by adding some structure and negative space, many gardeners could greatly improve the appearance and the impact of their gardens. However, in my opinion... FOLIAGE; its shape, size, and color will often create the greatest impact when planning and creating truly interesting professional looking gardens. The placement of foliage plants shouldn't be the after thought. They should often be considered and placed before any of the flowering ornamentals.
Perennials have their season of flowering. They offer interest in an ever changing garden sensory experience, and are sometimes followed by attractive seed heads in the late growing season. Many of them have very long flowering periods lasting a couple of months and can even change color with the changing temperatures. Annuals flower for most of the growing season, but never offer any interesting seasonal change. I tend to use them very sparingly if at all. When I do use them, I always mix them with seasonal perennials.
My favorite ornamental element is foliage. After designing with structure and negative space in place, I always start my landscape and gardening plans with the positioning of the foliage plants. This is actually included in the structural phase of my designing since many trees and shrubs have beautifully textured, shaped and colorful foliage; as well as the vast array of ornamental perennials and annuals. Just by adding a few well chosen foliage plants to one's ornamental composition, gardeners can vastly improve on the visual impact of their gardens.
Add large leaves to gardens with many small leaves, add shapely leaves to gardens with all similar leaves. Back your colorful flowers with contrasting foliage colors (don't forget that green is a color too). Just mix contrasting foliages together. And last but not least, mix in shrubs, trees and perennials that change color during the gardening seasons ... In my opinion, Autumn is the most glorious of the seasons. Once the gardener discovers how this trick really elevates their composition, they discover the key to great garden design.