My grandmother liked her flower beds planted in straight rows; short, medium and tall. Her flower bed designs consisted of straight lines and right angles. Today a more natural design style better reflects our environmentally friendly mindset. Curves, swishes and swirls, grouping and clusters of plants of varying heights and leaf textures can be observed in the landscape bed pictured below. Notice the placement of the tall, medium and short plant elements in the bed. The large mass of tall ornamental grass (green/white variegation) is placed to the back left of the bed. The finer textured, medium height, red colored grass is moved forward to mid-bed (front to back) and planted to the right side of the design. The groupings of ornamental grass form the skeleton or foundation of the bed. The void or open space within the bed has its own components flowing from the taller red coleus through the orange and yellow zinnias. Notice how the bed flows from back to front and left to right both in plant height and in color spectrum (red - orange - yellow). Also notice how the void extends across the entire width and completely from the front to back creating a window to view the landscape behind the bed. The small multi-trunk tree adds character and places a roof over the area providing a better sense of a "room" or alcove in the space.
A formal approach, using straight lines or geometric shapes also has a place in landscape bed design. The picture below illustrates a classic diamond shaped "hedge" interplanted with a plant of a different color and texture providing a strong contrast and increasing the emphasis on the pattern of the design. The picture is of a sample design. It could very easily be replicated multiple times down a much longer bed with the diamonds touching point to point. The 'Boxwood' cultivar of basil forms the line and a plume flowered, red foliage celosia provides the color and textured contrast.
In the picture below, the great deep, dark colored grass foliage contrasts with light and bright flowers. If you look closely you will see that the throat and veins in the petals of the 'Supertunia Vista Silverberry' petunias match, and repeat nicely, the dark maroon color of the foliage of the 'Vertigo' cultivar of Pennisetum grass.
Also notice the asymmetrical design with the Vertigo grass planted to the back left of the bed and the Vista Silverberry petunia flowing out to the front and extending around it to the right. This is a very simple design: two types of plants. A large mass to anchor the bed with an extensive void surround.