Is this primer suitable for rebar going into the ground, and need an enamel top coat? I am looking to install a rebar bottle tree in my garden.

We appreciate your interest, David. We don't recommend applying the Rust-Oleum Stops Rust Rusty Metal Primer over rebar as it is typically a galvanized surface. When you apply an alkyd oil-based paint over zinc plated or galvanized surfaces, a chemical reaction occurs between the two materials. This process, known as “saponification”, causes a build-up of the reaction product between the zinc and the paint. Over time, the paint will begin to peel off in large sheets. This can be avoided by using a latex-based primer such as the Rust-Oleum Stops Rust Universal Bonding Primer. The primer will act as a barrier coat and prevent the reaction from occurring. https://www.lowes.com/pd/Rust-Oleum-Stops-Rust-Universal-Bonding-Interior-Exterior-Bonding-Oil-Based-Primer-Actual-Net-Contents-12-fl-oz/50376756 - Rust-Oleum Product Support 5