The universal bracing strap is used between any 2 parallel straight joiners. It is not necessary to brace planters that are only 4 panels (square or rectangular) smaller than 47.25" on any side as long as there are no straight joiners used.
The 78.75" panel does require bracing. There are a few different options for bracing.
Option 1. You will need 1 rib (bracket) per 78.75" panel. This will be installed in the middle of the panel. It fits under the lip and is turned perpendicular to the panel. The rib drops into the hole on the bottom flange of the panel.
You can then use the Universal Bracing Strap to connect the 2 ribs in an X fashion
Option 2. You can use the large anchor post in conjunction with the pair of anchor set parts. You will not need ribs for this option. This option can also be use to brace any panel you feel like you would like extra support.
Note If the width of your panel exceeds 47.25 inches, then the universal bracing strap will not work as it will not be long enough. You can then either use the universal brace (turnbuckle style) and hook it to the straight joiners. Or, you can use the large anchor post in conjunction with the anchor set parts.