Create the Shelves
Use table saw to square ends of 1 x 6 boards, then measure and mark the length needed for the shelves. Cut both boards at once, the set the boards on the brackets (Image 1). Align 1-1/4 from the end of the backboard. Make sure front of shelf is flush to ends of brackets, then secure with wood screws (Image 2).
Next, create a lower shelf to store flower and vegetable flats. First, secure a cedar 1 x 12 by clamping, then mark board at 38" (Image 3). Cut to length using a circular saw. Use table saw to rip a 45-degree angle about 1" wide (Image 4).
Rip a 1 x 6 to the same length as the shelf, but about 2" wide. This piece will act as a brace and a connection point where the angled shelf meets the back board. Use a level to mark the location of the bottom shelf.