Probably the most well known concept around spacing in gardens is Mel Bartholomew’s “Square Foot Gardening”. This first and foremost applies to vegetable gardens, but can be applicable to spacing in ornamental gardens as well. Here is an exploration of spacing for garden designs.
All plants ornamental or otherwise, need space to grow, and a minimum of twelve inches apart is generally a good growing space principal. Open spaces are critical, especially in dry Zen gardens where open spaces represent the open sea. In Japanese gardens, open spaces are often the center piece of Japanese gardens, while plants and stones provide the backdrop or outline.