Place the 96-inch-long branches in pairs on a work surface. For each pair, lay the branches parallel and 36 inches apart. These are the uprights for the arch. Each pair is one end of the arch, which will measure 36 inches deep, 70 inches wide and approximately 78 inches tall once installed in the garden. Modify the lengths of the branches to create an arch for your specific space.
Place one 36-inch twig across one end on each pair of uprights. Measure up 24, 48, and 72 inches from that end and place one twig across at each measurement on each pair. You should have four twigs across each upright located at 0, 24, 48 and 72 inches from one end. The end with the twig across it on each upright is the top.
Wrap the ends of the twigs to the uprights and tie them off at each joint tightly using garden twine. Trim off the excess twine with a knife.
Take the upright assemblies to the spot you plan to install them. Push the bottom ends of the uprights down into the ground approximately 18 inches deep. Position the upright assemblies parallel to each other approximately 70 inches apart.
Place the two 72-inch-long branches parallel to each other approximately 36 inches apart on a work surface. These are the top cross supports.
Lay the remaining four 36-inch twigs across the top cross supports. Place one across each end and the other two evenly spaced between them. These are the supports for the top. Tie the twigs to the top cross supports at each joint. Trim off the excess twine. This is the top support assembly.
Raise the top support assembly over the upright assemblies and center it with the help of a friend. Lower the assembly down on top of the uprights.
Wrap and tie the uprights to the top support assembly with garden twine. Trim off the excess twine.