Thanks Stew.
Yes, the rebar was 1/2". The ridges on it made it ~9/16" at the thickest parts.
The first image in the original post shows me boring holes ~8" into the ends of the 2X2. The rebar was ~20" long and was pushed into the ground. Even with soil soft from recent rains it needed a few taps from a hammer against a block of wood to drive it all the way home.
The trellis was attached to the two pieces of 2X2 at the base with three brass, 2" long #12 screws on each side.
Trellis Base Detail.jpg
The screws are on the back side of the trellis in this image.
jtk