Answer: The old adage of "Right plant, right place" is a good guide. First, determine the amount of light the location receives, as well as the soil type (in the continuum of sand, silt, and clay), degree of soil moisture retention (a factor of the soil type, topography, and amount of organic matter content), and your growing zone (plant hardiness rating). The characteristics of the site will help you narrow plant choices to those that will thrive there. Design considerations (i.e., height, width, color, and bloom season) usually come last on the list, because if the plant won't thrive on a particular site, there isn't much point in planting it. In practical terms, once you are familiar with plants that do well in your area, plant the ones you like and experiment a little to get the mix that works for you.
Keep in mind, too, that if you're heart is set on growing a plant that isn't suited to the soil (build a raised bed, add soil amendments, improve drainage), light exposure (prune surrounding vegetation or thin tree limbs), etc., you can modify the site to accommodate the plant...but it's a lot more work than just choosing something that will thrive there in the first place.
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