Answer: The easiest way to determine how to space trees or shrubs is to find their usual mature width and then space the plants far enough apart that the branches will touch (or overlap by a few feet). In the case of Tristania laurina, the average mature width is about 20'. So, if you plant them 15-20' apart they should have adequate room for growth, yet produce a dense screen. California Pepper typically grows between 20 and 40' in width (depending upon age and growing conditions. Based upon that, you can space the trees 15-20' apart so the tops will grow into one another. Crape Myrtles are so variable in size that it's hard to make a suggestion. But when you decide which cultivars to plant, take the average diameter of the canopy and space them so the branches barely touch when the trees are mature. This will give you an attractive looking planting without having the tree branches overwhelm one another.
Best wishes with your landscape!
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