When choosing plants for the garden we tend to think about the flowers rather than the overall shape of the plant. In order to create a harmonious design you need to mix the different shapes to include the dramatic vertical plants with others with horizontal forms. This is what Rebecca Sweet means by the sideways look as she explains in her article which I found on the Horticulture Magazine website.
When choosing a new plant to add to your garden, consider a selection that has an interesting or unique form or shape. Plants with horizontal forms serve many purposes though they may not appear as dramatic as those that stand vertical or spherical. And they look interesting nonetheless.
3 Reasons to Choose to Go Sideways in the Garden
1 Horizontal growing plants help to add a softer note to the garden.
2 The spreading nature of this gentle, horizontal form helps calm and link together plants with stronger shapes.
3 Horizontal shapes provide a sense of motion, helping to direct the line of sight from one side of the garden to the other.
See more at Horticulture Magazine
Feature photo: Rebecca Sweet