Uniformity of hardscape materials
I'm currently laboring to turn my neglected side yard into a nice side yard. But while I do that, my mind tends to wander and now I'm thinking about the design of my front yard. As I was tending to (i.e. mowing) the front yard I got to thinking about the "plan". I plan on getting rid of some of the grass and replacing it with planting beds. As the idea ferments in my brain, I've gotten stuck a little with the idea of bed outlines and whether the edging material should be uniform.
What I have: My front yard is about 15' deep by 35-40' wide. About 2 ft from the sidewalk is a small retaining wall (about 12 inches high). The wall is made of small granite blocks which are angular. Nearer the house are some planting beds and they are edged with river rocks which are round. The disparity of the materials isn't a problem because they're not serving the same purpose and aren't that close to each other.
What I want: One of my ideas is to create a bed along the edge of the driveway which would run from the wall towards the house. I was thinking of using more of the granite instead of the river rock to tie it into the wall. This bed wouldn't be contiguous with a bed along the house - there would be a narrow path separating it from a bed extending from the house. I was thinking of using the river rock as the edging material for this bed because it's there and I want to use some of the rock as a splash area for my downspouts which come down in roughly the sides of the house bed so I was just going to extend it into the edging.
Where I'm stuck: Would it look strange? Both materials (granite and river rock) are rock but they're very different. They would now be in relatively close proximity to each other and serving the same purpose (bed edging). I do like to have my beds edged with something so not putting something down isn't really an option.
I'm thinking of just ditching the river rock except for the splash downs and using it somewhere else in the yard but is that necessary? If it was rock and wood or some completely different materials, I wouldn't be as stressed but it seems like very different kinds of rock are another story. Am I making this a bigger problem than needs be? In your opinion, should edging of paths/beds be made of the same material when they're in the same small yard? What exceptions can be made and when?