Maybe I am a confused on how to do this.  When I do primitive planes as backgrounds, the floors work really nice and I can texture them.  However, when I do the vertical plane for the background, I have strangeness because the planes don't seem to work together.  I always have a white space at the transition.  How do I make them fit properly so there is a square edge back there?

In order to know how to address this it would be useful to have:
a) a screenshot of the problem
b) the "raw" bitmap that you want to use as a background
c) the dimensions of the plane and its shading tree

Have you considered simply compositing the backdrop in Photoshop or After Effetcs? Sometime it's just simpler to do it in that way

The white space is either the gap between the two planes or the graphic texture not meeting the edges properly. Try and bring the plane into the floor so they overlap. Another problem that can arise from using the vertical plane is the lighting not match the rest of the scene. You will need to adjust the lighting on the floor and vertical plane.

There is a scene called 'Cyclorama' which you can put your own textures to, which has a curved edge where both the ground and rear plane meet.

Or.. try and do a render without the vertical plane and save the image as PNG format then load the image into your paint program. This will only port the actual objects rendered in the scene with no background image. Within your paint program, add a layer for the background image and position it to where you like it.

I appreciate your information.  But you know, somebody's got to try to do it their way.  I have a few cyclorama backgrounds and some scene backgrounds, but they seem square to the back.   I want to move multiple  planes to where I want in relation to the character and props (lights and shadows please).  I have some jpg backgrounds that work with the edit backgrounds, but but they are not as  flexible.  I will have to think about it more...
  Thank you for your help.