Rhythm in planting beds is created by the space that plants have between them. This is a very important aspect of planting design and will greatly affect the final outcome of your landscaping. Plants placed twice their overall diameter apart (2 feet apart for a 1 foot plant, 6 feet apart for a 3 foot plant) place equal emphasis on the plant and the space between the plant.
So when you look at a row of 50 plants placed in this way, you see the plant bed (and the bark dust, any weeds, any trash, and any debris such as branches or leaves from overhead trees) as much as you see the plant. We certainly don’t want to plant things too close together for health reasons, (and with DeSantis doing your maintenance you wouldn’t have to worry about the weeds, trash, and other debris!), but we also don’t want to put plants so far apart that they don’t look like part of a larger plan.
The other factor to consider when placing plants is the species. When planting the same species, we want to place them close enough to each other so that they look like a unit, or so they look like they go together. When planting different species, we want to leave enough space so that we show the viewer that we intend to have two different elements.
Spacing can make a space feel larger or smaller. A long, narrow space with plants spaced twice their overall diameter can feel a lot longer because of the repetitive nature of the planting. That same space with constantly changing small groups of plants gives benchmarks of progress to the person walking and makes the walk not feel so long. This has the same effect as making a playlist to group the music you want to listen to instead of repeating the same song over and over.
~Trey McBride, BLA