I'm often asked about plant spacing. "How far apart should I plant them?" Frankly, there is no precise answer for any particular species. Important factors to consider include the size of the plants at planting time, the approximate size of the plants at maturity, whether you want them to grow together or maintain space between, how much money you can afford to spend, and your own degree of patience. Because variable factors are involved, I would more than likely give you a range of possible distances. But it's not that difficult to ascertain for yourself.
To figure planting distances, begin by determining the mature spread or width of your plants. You can get that information from garden books, our planting guides, nurseries and the internet. Conclude whether you want the plants to fill in or if you want space between them at maturity. If you want space between them, how much? Add the approximate diameter of one mature plant to the desired space between two mature plants. The distance you decide upon need not be precise, but it should be consistent. When you begin planting, measure from the center of one plant to the center of the next.